fix for #50317

[~andy/gtk] / gtk / gtktextiter.c

/* GTK - The GIMP Toolkit
 * gtktextiter.c Copyright (C) 2000 Red Hat, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * Modified by the GTK+ Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GTK+ Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GTK+ at ftp://ftp.gtk.org/pub/gtk/.
 */

#include "gtktextiter.h"
#include "gtktextbtree.h"
#include "gtktextiterprivate.h"
#include "gtkdebug.h"
#include <string.h>
#include <ctype.h>

#define FIX_OVERFLOWS(varname) if ((varname) == G_MININT) (varname) = G_MININT + 1

typedef struct _GtkTextRealIter GtkTextRealIter;

struct _GtkTextRealIter
{
  /* Always-valid information */
  GtkTextBTree *tree;
  GtkTextLine *line;
  /* At least one of these is always valid;
     if invalid, they are -1.

     If the line byte offset is valid, so is the segment byte offset;
     and ditto for char offsets. */
  gint line_byte_offset;
  gint line_char_offset;
  /* These two are valid if >= 0 */
  gint cached_char_index;
  gint cached_line_number;
  /* Stamps to detect the buffer changing under us */
  gint chars_changed_stamp;
  gint segments_changed_stamp;
  /* Valid if the segments_changed_stamp is up-to-date */
  GtkTextLineSegment *segment;     /* indexable segment we index */
  GtkTextLineSegment *any_segment; /* first segment in our location,
                                      maybe same as "segment" */
  /* One of these will always be valid if segments_changed_stamp is
     up-to-date. If invalid, they are -1.

     If the line byte offset is valid, so is the segment byte offset;
     and ditto for char offsets. */
  gint segment_byte_offset;
  gint segment_char_offset;
};

/* These "set" functions should not assume any fields
   other than the char stamp and the tree are valid.
*/
static void
iter_set_common (GtkTextRealIter *iter,
                 GtkTextLine *line)
{
  /* Update segments stamp */
  iter->segments_changed_stamp =
    _gtk_text_btree_get_segments_changed_stamp (iter->tree);

  iter->line = line;

  iter->line_byte_offset = -1;
  iter->line_char_offset = -1;
  iter->segment_byte_offset = -1;
  iter->segment_char_offset = -1;
  iter->cached_char_index = -1;
  iter->cached_line_number = -1;
}

static void
iter_set_from_byte_offset (GtkTextRealIter *iter,
                           GtkTextLine *line,
                           gint byte_offset)
{
  iter_set_common (iter, line);

  if (!_gtk_text_line_byte_locate (iter->line,
                                   byte_offset,
                                   &iter->segment,
                                   &iter->any_segment,
                                   &iter->segment_byte_offset,
                                   &iter->line_byte_offset))
    g_error ("Byte index %d is off the end of the line",
             byte_offset);
}

static void
iter_set_from_char_offset (GtkTextRealIter *iter,
                           GtkTextLine *line,
                           gint char_offset)
{
  iter_set_common (iter, line);

  if (!_gtk_text_line_char_locate (iter->line,
                                   char_offset,
                                   &iter->segment,
                                   &iter->any_segment,
                                   &iter->segment_char_offset,
                                   &iter->line_char_offset))
    g_error ("Char offset %d is off the end of the line",
             char_offset);
}

static void
iter_set_from_segment (GtkTextRealIter *iter,
                       GtkTextLine *line,
                       GtkTextLineSegment *segment)
{
  GtkTextLineSegment *seg;
  gint byte_offset;

  /* This could theoretically be optimized by computing all the iter
     fields in this same loop, but I'm skipping it for now. */
  byte_offset = 0;
  seg = line->segments;
  while (seg != segment)
    {
      byte_offset += seg->byte_count;
      seg = seg->next;
    }

  iter_set_from_byte_offset (iter, line, byte_offset);
}

/* This function ensures that the segment-dependent information is
   truly computed lazily; often we don't need to do the full make_real
   work. This ensures the btree and line are valid, but doesn't
   update the segments. */
static GtkTextRealIter*
gtk_text_iter_make_surreal (const GtkTextIter *_iter)
{
  GtkTextRealIter *iter = (GtkTextRealIter*)_iter;

  if (iter->chars_changed_stamp !=
      _gtk_text_btree_get_chars_changed_stamp (iter->tree))
    {
      g_warning ("Invalid text buffer iterator: either the iterator "
                 "is uninitialized, or the characters/pixbufs/widgets "
                 "in the buffer have been modified since the iterator "
                 "was created.\nYou must use marks, character numbers, "
                 "or line numbers to preserve a position across buffer "
                 "modifications.\nYou can apply tags and insert marks "
                 "without invalidating your iterators,\n"
                 "but any mutation that affects 'indexable' buffer contents "
                 "(contents that can be referred to by character offset)\n"
                 "will invalidate all outstanding iterators");
      return NULL;
    }

  /* We don't update the segments information since we are becoming
     only surreal. However we do invalidate the segments information
     if appropriate, to be sure we segfault if we try to use it and we
     should have used make_real. */

  if (iter->segments_changed_stamp !=
      _gtk_text_btree_get_segments_changed_stamp (iter->tree))
    {
      iter->segment = NULL;
      iter->any_segment = NULL;
      /* set to segfault-causing values. */
      iter->segment_byte_offset = -10000;
      iter->segment_char_offset = -10000;
    }

  return iter;
}

static GtkTextRealIter*
gtk_text_iter_make_real (const GtkTextIter *_iter)
{
  GtkTextRealIter *iter;

  iter = gtk_text_iter_make_surreal (_iter);

  if (iter->segments_changed_stamp !=
      _gtk_text_btree_get_segments_changed_stamp (iter->tree))
    {
      if (iter->line_byte_offset >= 0)
        {
          iter_set_from_byte_offset (iter,
                                     iter->line,
                                     iter->line_byte_offset);
        }
      else
        {
          g_assert (iter->line_char_offset >= 0);

          iter_set_from_char_offset (iter,
                                     iter->line,
                                     iter->line_char_offset);
        }
    }

  g_assert (iter->segment != NULL);
  g_assert (iter->any_segment != NULL);
  g_assert (iter->segment->char_count > 0);

  return iter;
}

static GtkTextRealIter*
iter_init_common (GtkTextIter *_iter,
                  GtkTextBTree *tree)
{
  GtkTextRealIter *iter = (GtkTextRealIter*)_iter;

  g_return_val_if_fail (iter != NULL, NULL);
  g_return_val_if_fail (tree != NULL, NULL);

  iter->tree = tree;

  iter->chars_changed_stamp =
    _gtk_text_btree_get_chars_changed_stamp (iter->tree);

  return iter;
}

static GtkTextRealIter*
iter_init_from_segment (GtkTextIter *iter,
                        GtkTextBTree *tree,
                        GtkTextLine *line,
                        GtkTextLineSegment *segment)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (line != NULL, NULL);

  real = iter_init_common (iter, tree);

  iter_set_from_segment (real, line, segment);

  return real;
}

static GtkTextRealIter*
iter_init_from_byte_offset (GtkTextIter *iter,
                            GtkTextBTree *tree,
                            GtkTextLine *line,
                            gint line_byte_offset)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (line != NULL, NULL);

  real = iter_init_common (iter, tree);

  iter_set_from_byte_offset (real, line, line_byte_offset);

  if (real->segment->type == &gtk_text_char_type &&
      (real->segment->body.chars[real->segment_byte_offset] & 0xc0) == 0x80)
    g_warning ("Incorrect line byte index %d falls in the middle of a UTF-8 "
               "character; this will crash the text buffer. "
               "Byte indexes must refer to the start of a character.",
               line_byte_offset);
  
  return real;
}

static GtkTextRealIter*
iter_init_from_char_offset (GtkTextIter *iter,
                            GtkTextBTree *tree,
                            GtkTextLine *line,
                            gint line_char_offset)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (line != NULL, NULL);

  real = iter_init_common (iter, tree);

  iter_set_from_char_offset (real, line, line_char_offset);

  return real;
}

static inline void
invalidate_segment (GtkTextRealIter *iter)
{
  iter->segments_changed_stamp -= 1;
}

static inline void
invalidate_char_index (GtkTextRealIter *iter)
{
  iter->cached_char_index = -1;
}

static inline void
invalidate_line_number (GtkTextRealIter *iter)
{
  iter->cached_line_number = -1;
}

static inline void
adjust_char_index (GtkTextRealIter *iter, gint count)
{
  if (iter->cached_char_index >= 0)
    iter->cached_char_index += count;
}

static inline void
adjust_line_number (GtkTextRealIter *iter, gint count)
{
  if (iter->cached_line_number >= 0)
    iter->cached_line_number += count;
}

static inline void
adjust_char_offsets (GtkTextRealIter *iter, gint count)
{
  if (iter->line_char_offset >= 0)
    {
      iter->line_char_offset += count;
      g_assert (iter->segment_char_offset >= 0);
      iter->segment_char_offset += count;
    }
}

static inline void
adjust_byte_offsets (GtkTextRealIter *iter, gint count)
{
  if (iter->line_byte_offset >= 0)
    {
      iter->line_byte_offset += count;
      g_assert (iter->segment_byte_offset >= 0);
      iter->segment_byte_offset += count;
    }
}

static inline void
ensure_char_offsets (GtkTextRealIter *iter)
{
  if (iter->line_char_offset < 0)
    {
      g_assert (iter->line_byte_offset >= 0);

      _gtk_text_line_byte_to_char_offsets (iter->line,
                                          iter->line_byte_offset,
                                          &iter->line_char_offset,
                                          &iter->segment_char_offset);
    }
}

static inline void
ensure_byte_offsets (GtkTextRealIter *iter)
{
  if (iter->line_byte_offset < 0)
    {
      g_assert (iter->line_char_offset >= 0);

      _gtk_text_line_char_to_byte_offsets (iter->line,
                                          iter->line_char_offset,
                                          &iter->line_byte_offset,
                                          &iter->segment_byte_offset);
    }
}

static inline gboolean
is_segment_start (GtkTextRealIter *real)
{
  return real->segment_byte_offset == 0 || real->segment_char_offset == 0;
}

#if 1
static void
check_invariants (const GtkTextIter *iter)
{
  if (gtk_debug_flags & GTK_DEBUG_TEXT)
    _gtk_text_iter_check (iter);
}
#else
#define check_invariants (x)
#endif

/**
 * gtk_text_iter_get_buffer:
 * @iter: an iterator
 *
 * Return the #GtkTextBuffer this iterator is associated with
 *
 * Return value: the buffer
 **/
GtkTextBuffer*
gtk_text_iter_get_buffer (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  return _gtk_text_btree_get_buffer (real->tree);
}

/**
 * gtk_text_iter_copy:
 * @iter: an iterator
 *
 * Create a dynamically-allocated copy of an iterator. This function
 * is not useful in applications, because iterators can be copied with a
 * simple assignment (<literal>GtkTextIter i = j;</literal>). The
 * function is used by language bindings.
 *
 * Return value: a copy of the @iter, free with gtk_text_iter_free ()
 **/
GtkTextIter*
gtk_text_iter_copy (const GtkTextIter *iter)
{
  GtkTextIter *new_iter;

  g_return_val_if_fail (iter != NULL, NULL);

  new_iter = g_new (GtkTextIter, 1);

  *new_iter = *iter;

  return new_iter;
}

/**
 * gtk_text_iter_free:
 * @iter: a dynamically-allocated iterator
 *
 * Free an iterator allocated on the heap. This function
 * is intended for use in language bindings, and is not
 * especially useful for applications, because iterators can
 * simply be allocated on the stack.
 *
 **/
void
gtk_text_iter_free (GtkTextIter *iter)
{
  g_return_if_fail (iter != NULL);

  g_free (iter);
}

GtkTextLineSegment*
_gtk_text_iter_get_indexable_segment (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  g_assert (real->segment != NULL);

  return real->segment;
}

GtkTextLineSegment*
_gtk_text_iter_get_any_segment (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  g_assert (real->any_segment != NULL);

  return real->any_segment;
}

gint
_gtk_text_iter_get_segment_byte (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  ensure_byte_offsets (real);

  check_invariants (iter);

  return real->segment_byte_offset;
}

gint
_gtk_text_iter_get_segment_char (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  ensure_char_offsets (real);

  check_invariants (iter);

  return real->segment_char_offset;
}

/* This function does not require a still-valid
   iterator */
GtkTextLine*
_gtk_text_iter_get_text_line (const GtkTextIter *iter)
{
  const GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = (const GtkTextRealIter*)iter;

  return real->line;
}

/* This function does not require a still-valid
   iterator */
GtkTextBTree*
_gtk_text_iter_get_btree (const GtkTextIter *iter)
{
  const GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = (const GtkTextRealIter*)iter;

  return real->tree;
}

/*
 * Conversions
 */

/**
 * gtk_text_iter_get_offset:
 * @iter: an iterator
 *
 * Returns the character offset of an iterator.
 * Each character in a #GtkTextBuffer has an offset,
 * starting with 0 for the first character in the buffer.
 * Use gtk_text_buffer_get_iter_at_offset () to convert an
 * offset back into an iterator.
 *
 * Return value: a character offset
 **/
gint
gtk_text_iter_get_offset (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  check_invariants (iter);
  
  if (real->cached_char_index < 0)
    {
      ensure_char_offsets (real);
      
      real->cached_char_index =
        _gtk_text_line_char_index (real->line);
      real->cached_char_index += real->line_char_offset;
    }

  check_invariants (iter);

  return real->cached_char_index;
}

/**
 * gtk_text_iter_get_line:
 * @iter: an iterator
 *
 * Returns the line number containing the iterator. Lines in
 * a #GtkTextBuffer are numbered beginning with 0 for the first
 * line in the buffer.
 *
 * Return value: a line number
 **/
gint
gtk_text_iter_get_line (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  if (real->cached_line_number < 0)
    real->cached_line_number =
      _gtk_text_line_get_number (real->line);

  check_invariants (iter);

  return real->cached_line_number;
}

/**
 * gtk_text_iter_get_line_offset:
 * @iter: an iterator
 *
 * Returns the character offset of the iterator,
 * counting from the start of a newline-terminated line.
 * The first character on the line has offset 0.
 *
 * Return value: offset from start of line
 **/
gint
gtk_text_iter_get_line_offset (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  ensure_char_offsets (real);

  check_invariants (iter);

  return real->line_char_offset;
}

/**
 * gtk_text_iter_get_line_index:
 * @iter: an iterator
 *
 * Returns the byte index of the iterator, counting
 * from the start of a newline-terminated line.
 * Remember that #GtkTextBuffer encodes text in
 * UTF-8, and that characters can require a variable
 * number of bytes to represent.
 *
 * Return value: distance from start of line, in bytes
 **/
gint
gtk_text_iter_get_line_index (const GtkTextIter *iter)
{
  GtkTextRealIter *real;
  
  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  ensure_byte_offsets (real);

  check_invariants (iter);

  return real->line_byte_offset;
}

/**
 * gtk_text_iter_get_visible_line_offset:
 * @iter: a #GtkTextIter
 * 
 * Returns the offset in characters from the start of the
 * line to the given @iter, not counting characters that
 * are invisible due to tags with the "invisible" flag
 * toggled on.
 * 
 * Return value: offset in visible characters from the start of the line 
 **/
gint
gtk_text_iter_get_visible_line_offset (const GtkTextIter *iter)
{
  GtkTextRealIter *real;
  gint vis_offset;
  GtkTextLineSegment *seg;
  GtkTextIter pos;
  
  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  ensure_char_offsets (real);

  check_invariants (iter);

  vis_offset = real->line_char_offset;

  _gtk_text_btree_get_iter_at_line (real->tree,
                                    &pos,
                                    real->line,
                                    0);

  seg = _gtk_text_iter_get_indexable_segment (&pos);

  while (seg != real->segment)
    {
      /* This is a pretty expensive call, making the
       * whole function pretty lame; we could keep track
       * of current invisibility state by looking at toggle
       * segments as we loop, and then call this function
       * only once per line, in order to speed up the loop
       * quite a lot.
       */
      if (_gtk_text_btree_char_is_invisible (&pos))
        vis_offset -= seg->char_count;

      _gtk_text_iter_forward_indexable_segment (&pos);

      seg = _gtk_text_iter_get_indexable_segment (&pos);
    }

  if (_gtk_text_btree_char_is_invisible (&pos))
    vis_offset -= real->segment_char_offset;
  
  return vis_offset;
}


/**
 * gtk_text_iter_get_visible_line_index:
 * @iter: a #GtkTextIter
 * 
 * Returns the number of bytes from the start of the
 * line to the given @iter, not counting bytes that
 * are invisible due to tags with the "invisible" flag
 * toggled on.
 * 
 * Return value: byte index of @iter with respect to the start of the line
 **/
gint
gtk_text_iter_get_visible_line_index (const GtkTextIter *iter)
{
  GtkTextRealIter *real;
  gint vis_offset;
  GtkTextLineSegment *seg;
  GtkTextIter pos;
  
  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  ensure_char_offsets (real);

  check_invariants (iter);

  vis_offset = real->line_byte_offset;

  _gtk_text_btree_get_iter_at_line (real->tree,
                                    &pos,
                                    real->line,
                                    0);

  seg = _gtk_text_iter_get_indexable_segment (&pos);

  while (seg != real->segment)
    {
      /* This is a pretty expensive call, making the
       * whole function pretty lame; we could keep track
       * of current invisibility state by looking at toggle
       * segments as we loop, and then call this function
       * only once per line, in order to speed up the loop
       * quite a lot.
       */
      if (_gtk_text_btree_char_is_invisible (&pos))
        vis_offset -= seg->byte_count;

      _gtk_text_iter_forward_indexable_segment (&pos);

      seg = _gtk_text_iter_get_indexable_segment (&pos);
    }

  if (_gtk_text_btree_char_is_invisible (&pos))
    vis_offset -= real->segment_byte_offset;
  
  return vis_offset;
}

/*
 * Dereferencing
 */

/**
 * gtk_text_iter_get_char:
 * @iter: an iterator
 *
 * Returns the Unicode character at this iterator.  (Equivalent to
 * operator* on a C++ iterator.)  If the iterator points at a
 * non-character element, such as an image embedded in the buffer, the
 * Unicode "unknown" character 0xFFFC is returned. If invoked on
 * the end iterator, zero is returned; zero is not a valid Unicode character.
 * So you can write a loop which ends when gtk_text_iter_get_char ()
 * returns 0.
 *
 * Return value: a Unicode character, or 0 if @iter is not dereferenceable
 **/
gunichar
gtk_text_iter_get_char (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  check_invariants (iter);

  if (gtk_text_iter_is_end (iter))
    return 0;
  else if (real->segment->type == &gtk_text_char_type)
    {
      ensure_byte_offsets (real);
      
      return g_utf8_get_char (real->segment->body.chars +
                              real->segment_byte_offset);
    }
  else
    {
      /* Unicode "unknown character" 0xFFFC */
      return GTK_TEXT_UNKNOWN_CHAR;
    }
}

/**
 * gtk_text_iter_get_slice:
 * @start: iterator at start of a range
 * @end: iterator at end of a range
 *
 * Returns the text in the given range. A "slice" is an array of
 * characters encoded in UTF-8 format, including the Unicode "unknown"
 * character 0xFFFC for iterable non-character elements in the buffer,
 * such as images.  Because images are encoded in the slice, byte and
 * character offsets in the returned array will correspond to byte
 * offsets in the text buffer. Note that 0xFFFC can occur in normal
 * text as well, so it is not a reliable indicator that a pixbuf or
 * widget is in the buffer.
 *
 * Return value: slice of text from the buffer
 **/
gchar*
gtk_text_iter_get_slice       (const GtkTextIter *start,
                               const GtkTextIter *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return _gtk_text_btree_get_text (start, end, TRUE, TRUE);
}

/**
 * gtk_text_iter_get_text:
 * @start: iterator at start of a range
 * @end: iterator at end of a range
 *
 * Returns <emphasis>text</emphasis> in the given range.  If the range
 * contains non-text elements such as images, the character and byte
 * offsets in the returned string will not correspond to character and
 * byte offsets in the buffer. If you want offsets to correspond, see
 * gtk_text_iter_get_slice ().
 *
 * Return value: array of characters from the buffer
 **/
gchar*
gtk_text_iter_get_text       (const GtkTextIter *start,
                              const GtkTextIter *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return _gtk_text_btree_get_text (start, end, TRUE, FALSE);
}

/**
 * gtk_text_iter_get_visible_slice:
 * @start: iterator at start of range
 * @end: iterator at end of range
 *
 * Like gtk_text_iter_get_slice (), but invisible text is not included.
 * Invisible text is usually invisible because a #GtkTextTag with the
 * "invisible" attribute turned on has been applied to it.
 *
 * Return value: slice of text from the buffer
 **/
gchar*
gtk_text_iter_get_visible_slice (const GtkTextIter  *start,
                                 const GtkTextIter  *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return _gtk_text_btree_get_text (start, end, FALSE, TRUE);
}

/**
 * gtk_text_iter_get_visible_text:
 * @start: iterator at start of range
 * @end: iterator at end of range
 *
 * Like gtk_text_iter_get_text (), but invisible text is not included.
 * Invisible text is usually invisible because a #GtkTextTag with the
 * "invisible" attribute turned on has been applied to it.
 *
 * Return value: string containing visible text in the range
 **/
gchar*
gtk_text_iter_get_visible_text (const GtkTextIter  *start,
                                const GtkTextIter  *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return _gtk_text_btree_get_text (start, end, FALSE, FALSE);
}

/**
 * gtk_text_iter_get_pixbuf:
 * @iter: an iterator
 *
 * If the location pointed to by @iter contains a pixbuf, the pixbuf
 * is returned (with no new reference count added). Otherwise,
 * NULL is returned.
 *
 * Return value: the pixbuf at @iter
 **/
GdkPixbuf*
gtk_text_iter_get_pixbuf (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  if (real->segment->type != &gtk_text_pixbuf_type)
    return NULL;
  else
    return real->segment->body.pixbuf.pixbuf;
}

/**
 * gtk_text_iter_get_child_anchor:
 * @iter: an iterator
 *
 * If the location pointed to by @iter contains a child anchor, the
 * anchor is returned (with no new reference count added). Otherwise,
 * NULL is returned.
 *
 * Return value: the anchor at @iter
 **/
GtkTextChildAnchor*
gtk_text_iter_get_child_anchor (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  if (real->segment->type != &gtk_text_child_type)
    return NULL;
  else
    return real->segment->body.child.obj;
}

/**
 * gtk_text_iter_get_marks:
 * @iter: an iterator
 *
 * Returns a list of all #GtkTextMark at this location. Because marks
 * are not iterable (they don't take up any "space" in the buffer,
 * they are just marks in between iterable locations), multiple marks
 * can exist in the same place. The returned list is not in any
 * meaningful order.
 *
 * Return value: list of #GtkTextMark
 **/
GSList*
gtk_text_iter_get_marks (const GtkTextIter *iter)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;
  GSList *retval;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  retval = NULL;
  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (seg->type == &gtk_text_left_mark_type ||
          seg->type == &gtk_text_right_mark_type)
        retval = g_slist_prepend (retval, seg->body.mark.obj);

      seg = seg->next;
    }

  /* The returned list isn't guaranteed to be in any special order,
     and it isn't. */
  return retval;
}

/**
 * gtk_text_iter_get_toggled_tags:
 * @iter: an iterator
 * @toggled_on: TRUE to get toggled-on tags
 *
 * Returns a list of #GtkTextTag that are toggled on or off at this
 * point.  (If @toggled_on is TRUE, the list contains tags that are
 * toggled on.) If a tag is toggled on at @iter, then some non-empty
 * range of characters following @iter has that tag applied to it.  If
 * a tag is toggled off, then some non-empty range following @iter
 * does <emphasis>not</emphasis> have the tag applied to it.
 *
 * Return value: tags toggled at this point
 **/
GSList*
gtk_text_iter_get_toggled_tags  (const GtkTextIter  *iter,
                                 gboolean            toggled_on)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;
  GSList *retval;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  retval = NULL;
  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (toggled_on)
        {
          if (seg->type == &gtk_text_toggle_on_type)
            {
              retval = g_slist_prepend (retval, seg->body.toggle.info->tag);
            }
        }
      else
        {
          if (seg->type == &gtk_text_toggle_off_type)
            {
              retval = g_slist_prepend (retval, seg->body.toggle.info->tag);
            }
        }

      seg = seg->next;
    }

  /* The returned list isn't guaranteed to be in any special order,
     and it isn't. */
  return retval;
}

/**
 * gtk_text_iter_begins_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag, or NULL
 *
 * Returns TRUE if @tag is toggled on at exactly this point. If @tag
 * is NULL, returns TRUE if any tag is toggled on at this point. Note
 * that the gtk_text_iter_begins_tag () returns TRUE if @iter is the
 * <emphasis>start</emphasis> of the tagged range;
 * gtk_text_iter_has_tag () tells you whether an iterator is
 * <emphasis>within</emphasis> a tagged range.
 *
 * Return value: whether @iter is the start of a range tagged with @tag
 **/
gboolean
gtk_text_iter_begins_tag    (const GtkTextIter  *iter,
                             GtkTextTag         *tag)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (seg->type == &gtk_text_toggle_on_type)
        {
          if (tag == NULL ||
              seg->body.toggle.info->tag == tag)
            return TRUE;
        }

      seg = seg->next;
    }

  return FALSE;
}

/**
 * gtk_text_iter_ends_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag, or NULL
 *
 * Returns TRUE if @tag is toggled off at exactly this point. If @tag
 * is NULL, returns TRUE if any tag is toggled off at this point. Note
 * that the gtk_text_iter_ends_tag () returns TRUE if @iter is the
 * <emphasis>end</emphasis> of the tagged range;
 * gtk_text_iter_has_tag () tells you whether an iterator is
 * <emphasis>within</emphasis> a tagged range.
 *
 * Return value: whether @iter is the end of a range tagged with @tag
 *
 **/
gboolean
gtk_text_iter_ends_tag   (const GtkTextIter  *iter,
                          GtkTextTag         *tag)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (seg->type == &gtk_text_toggle_off_type)
        {
          if (tag == NULL ||
              seg->body.toggle.info->tag == tag)
            return TRUE;
        }

      seg = seg->next;
    }

  return FALSE;
}

/**
 * gtk_text_iter_toggles_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag, or NULL
 *
 * This is equivalent to (gtk_text_iter_begins_tag () ||
 * gtk_text_iter_ends_tag ()), i.e. it tells you whether a range with
 * @tag applied to it begins <emphasis>or</emphasis> ends at @iter.
 *
 * Return value: whether @tag is toggled on or off at @iter
 **/
gboolean
gtk_text_iter_toggles_tag (const GtkTextIter  *iter,
                           GtkTextTag         *tag)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  seg = real->any_segment;
  while (seg != real->segment)
    {
      if ( (seg->type == &gtk_text_toggle_off_type ||
            seg->type == &gtk_text_toggle_on_type) &&
           (tag == NULL ||
            seg->body.toggle.info->tag == tag) )
        return TRUE;

      seg = seg->next;
    }

  return FALSE;
}

/**
 * gtk_text_iter_has_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag
 *
 * Returns TRUE if @iter is within a range tagged with @tag.
 *
 * Return value: whether @iter is tagged with @tag
 **/
gboolean
gtk_text_iter_has_tag (const GtkTextIter   *iter,
                       GtkTextTag          *tag)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_TEXT_TAG (tag), FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (real->line_byte_offset >= 0)
    {
      return _gtk_text_line_byte_has_tag (real->line, real->tree,
                                          real->line_byte_offset, tag);
    }
  else
    {
      g_assert (real->line_char_offset >= 0);
      return _gtk_text_line_char_has_tag (real->line, real->tree,
                                          real->line_char_offset, tag);
    }
}

/**
 * gtk_text_iter_get_tags:
 * @iter: a #GtkTextIter
 * 
 * Returns a list of tags that apply to @iter, in ascending order of
 * priority (highest-priority tags are last). The #GtkTextTag in the
 * list don't have a reference added, but you have to free the list
 * itself.
 * 
 * Return value: list of #GtkTextTag
 **/
GSList*
gtk_text_iter_get_tags (const GtkTextIter *iter)
{
  GtkTextTag** tags;
  gint tag_count = 0;
  gint i;
  GSList *retval;
  
  g_return_val_if_fail (iter != NULL, NULL);
  
  /* Get the tags at this spot */
  tags = _gtk_text_btree_get_tags (iter, &tag_count);

  /* No tags, use default style */
  if (tags == NULL || tag_count == 0)
    {
      if (tags)
        g_free (tags);

      return NULL;
    }

  /* Sort tags in ascending order of priority */
  _gtk_text_tag_array_sort (tags, tag_count);

  retval = NULL;
  i = 0;
  while (i < tag_count)
    {
      retval = g_slist_prepend (retval, tags[i]);
      ++i;
    }
  
  g_free (tags);

  /* Return tags in ascending order of priority */
  return g_slist_reverse (retval);
}

/**
 * gtk_text_iter_editable:
 * @iter: an iterator
 * @default_setting: %TRUE if text is editable by default
 *
 * Returns whether the character at @iter is within an editable region
 * of text.  Non-editable text is "locked" and can't be changed by the
 * user via #GtkTextView. This function is simply a convenience
 * wrapper around gtk_text_iter_get_attributes (). If no tags applied
 * to this text affect editability, @default_setting will be returned.
 *
 * You don't want to use this function to decide whether text can be
 * inserted at @iter, because for insertion you don't want to know
 * whether the char at @iter is inside an editable range, you want to
 * know whether a new character inserted at @iter would be inside an
 * editable range. Use gtk_text_iter_can_insert() to handle this
 * case.
 * 
 * Return value: whether @iter is inside an editable range
 **/
gboolean
gtk_text_iter_editable (const GtkTextIter *iter,
                        gboolean           default_setting)
{
  GtkTextAttributes *values;
  gboolean retval;

  g_return_val_if_fail (iter != NULL, FALSE);
  
  values = gtk_text_attributes_new ();

  values->editable = default_setting;

  gtk_text_iter_get_attributes (iter, values);

  retval = values->editable;

  gtk_text_attributes_unref (values);

  return retval;
}

/**
 * gtk_text_iter_can_insert:
 * @iter: an iterator
 * @default_editability: %TRUE if text is editable by default
 * 
 * Considering the default editability of the buffer, and tags that
 * affect editability, determines whether text inserted at @iter would
 * be editable. If text inserted at @iter would be editable then the
 * user should be allowed to insert text at @iter.
 * gtk_text_buffer_insert_interactive() uses this function to decide
 * whether insertions are allowed at a given position.
 * 
 * Return value: whether text inserted at @iter would be editable
 **/
gboolean
gtk_text_iter_can_insert (const GtkTextIter *iter,
                          gboolean           default_editability)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  
  if (gtk_text_iter_editable (iter, default_editability))
    return TRUE;
  /* If at start/end of buffer, default editability is used */
  else if ((gtk_text_iter_is_start (iter) ||
            gtk_text_iter_is_end (iter)) &&
           default_editability)
    return TRUE;
  else
    {
      /* if iter isn't editable, and the char before iter is,
       * then iter is the first char in an editable region
       * and thus insertion at iter results in editable text.
       */
      GtkTextIter prev = *iter;
      gtk_text_iter_backward_char (&prev);
      return gtk_text_iter_editable (&prev, default_editability);
    }
}


/**
 * gtk_text_iter_get_language:
 * @iter: an iterator
 *
 * A convenience wrapper around gtk_text_iter_get_attributes (),
 * which returns the language in effect at @iter. If no tags affecting
 * language * apply to @iter, the return value is identical to that of
 * gtk_get_default_language ().
 *
 * Return value: language in effect at @iter
 **/
PangoLanguage *
gtk_text_iter_get_language (const GtkTextIter *iter)
{
  GtkTextAttributes *values;
  PangoLanguage *retval;
  
  values = gtk_text_attributes_new ();

  gtk_text_iter_get_attributes (iter, values);

  retval = values->language;

  gtk_text_attributes_unref (values);

  return retval;
}

/**
 * gtk_text_iter_starts_line:
 * @iter: an iterator
 *
 * Returns TRUE if @iter begins a paragraph,
 * i.e. if gtk_text_iter_get_line_offset () would return 0.
 * However this function is potentially more efficient than
 * gtk_text_iter_get_line_offset () because it doesn't have to compute
 * the offset, it just has to see whether it's 0.
 *
 * Return value: whether @iter begins a line
 **/
gboolean
gtk_text_iter_starts_line (const GtkTextIter   *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (real->line_byte_offset >= 0)
    {
      return (real->line_byte_offset == 0);
    }
  else
    {
      g_assert (real->line_char_offset >= 0);
      return (real->line_char_offset == 0);
    }
}

/**
 * gtk_text_iter_ends_line:
 * @iter: an iterator
 *
 * Returns TRUE if @iter points to the start of the paragraph delimiter
 * characters for a line (delimiters will be either a newline, a
 * carriage return, a carriage return followed by a newline, or a
 * Unicode paragraph separator character). Note that an iterator pointing
 * to the \n of a \r\n pair will not be counted as the end of a line,
 * the line ends before the \r.
 *
 * Return value: whether @iter is at the end of a line
 **/
gboolean
gtk_text_iter_ends_line (const GtkTextIter   *iter)
{
  GtkTextRealIter *real;
  gunichar wc;
  
  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);
  
  check_invariants (iter);

  /* Only one character has type G_UNICODE_PARAGRAPH_SEPARATOR in
   * Unicode 3.0; update this if that changes.
   */
#define PARAGRAPH_SEPARATOR 0x2029

  wc = gtk_text_iter_get_char (iter);
  
  if (wc == '\r' || wc == PARAGRAPH_SEPARATOR)
    return TRUE;
  else if (wc == '\n')
    {
      /* need to determine if a \r precedes the \n, in which case
       * we aren't the end of the line
       */
      GtkTextIter tmp = *iter;
      if (!gtk_text_iter_backward_char (&tmp))
        return TRUE;

      return gtk_text_iter_get_char (&tmp) != '\r';
    }
  else
    return FALSE;
}

/**
 * gtk_text_iter_is_end:
 * @iter: an iterator
 *
 * Returns TRUE if @iter is the end iterator, i.e. one past the last
 * dereferenceable iterator in the buffer. gtk_text_iter_is_end () is
 * the most efficient way to check whether an iterator is the end
 * iterator.
 *
 * Return value: whether @iter is the end iterator
 **/
gboolean
gtk_text_iter_is_end (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (!_gtk_text_line_contains_end_iter (real->line, real->tree))
    return FALSE;

  /* Now we need the segments validated */
  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;
  
  return _gtk_text_btree_is_end (real->tree, real->line,
                                 real->segment,
                                 real->segment_byte_offset,
                                 real->segment_char_offset);
}

/**
 * gtk_text_iter_is_start:
 * @iter: an iterator
 *
 * Returns TRUE if @iter is the first iterator in the buffer, that is
 * if @iter has a character offset of 0.
 *
 * Return value: whether @iter is the first in the buffer
 **/
gboolean
gtk_text_iter_is_start (const GtkTextIter *iter)
{
  return gtk_text_iter_get_offset (iter) == 0;
}

/**
 * gtk_text_iter_get_chars_in_line:
 * @iter: an iterator
 *
 * Returns the number of characters in the line containing @iter,
 * including the paragraph delimiters.
 *
 * Return value: number of characters in the line
 **/
gint
gtk_text_iter_get_chars_in_line (const GtkTextIter   *iter)
{
  GtkTextRealIter *real;
  gint count;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  check_invariants (iter);

  if (real->line_char_offset >= 0)
    {
      /* We can start at the segments we've already found. */
      count = real->line_char_offset - real->segment_char_offset;
      seg = _gtk_text_iter_get_indexable_segment (iter);
    }
  else
    {
      /* count whole line. */
      seg = real->line->segments;
      count = 0;
    }


  while (seg != NULL)
    {
      count += seg->char_count;

      seg = seg->next;
    }

  return count;
}

/**
 * gtk_text_iter_get_bytes_in_line:
 * @iter: an iterator
 *
 * Returns the number of bytes in the line containing @iter,
 * including the paragraph delimiters.
 *
 * Return value: number of bytes in the line
 **/
gint
gtk_text_iter_get_bytes_in_line (const GtkTextIter   *iter)
{
  GtkTextRealIter *real;
  gint count;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  check_invariants (iter);

  if (real->line_byte_offset >= 0)
    {
      /* We can start at the segments we've already found. */
      count = real->line_byte_offset - real->segment_byte_offset;
      seg = _gtk_text_iter_get_indexable_segment (iter);
    }
  else
    {
      /* count whole line. */
      seg = real->line->segments;
      count = 0;
    }

  while (seg != NULL)
    {
      count += seg->byte_count;

      seg = seg->next;
    }

  return count;
}

/**
 * gtk_text_iter_get_attributes:
 * @iter: an iterator
 * @values: a #GtkTextAttributes to be filled in
 *
 * Computes the effect of any tags applied to this spot in the
 * text. The @values parameter should be initialized to the default
 * settings you wish to use if no tags are in effect. You'd typically
 * obtain the defaults from gtk_text_view_get_default_attributes().
 *
 * gtk_text_iter_get_attributes () will modify @values, applying the
 * effects of any tags present at @iter. If any tags affected @values,
 * the function returns %TRUE.
 *
 * Return value: %TRUE if @values was modified
 **/
gboolean
gtk_text_iter_get_attributes (const GtkTextIter  *iter,
                              GtkTextAttributes  *values)
{
  GtkTextTag** tags;
  gint tag_count = 0;

  /* Get the tags at this spot */
  tags = _gtk_text_btree_get_tags (iter, &tag_count);

  /* No tags, use default style */
  if (tags == NULL || tag_count == 0)
    {
      if (tags)
        g_free (tags);

      return FALSE;
    }

  /* Sort tags in ascending order of priority */
  _gtk_text_tag_array_sort (tags, tag_count);

  _gtk_text_attributes_fill_from_tags (values,
                                       tags,
                                       tag_count);

  g_free (tags);

  return TRUE;
}

/*
 * Increments/decrements
 */

/* The return value of this indicates WHETHER WE MOVED.
 * The return value of public functions indicates
 * (MOVEMENT OCCURRED && NEW ITER IS DEREFERENCEABLE)
 *
 * This function will not change the iterator if
 * it's already on the last (end iter) line, i.e. it
 * won't move to the end of the last line.
 */
static gboolean
forward_line_leaving_caches_unmodified (GtkTextRealIter *real)
{
  if (!_gtk_text_line_contains_end_iter (real->line, real->tree))
    {
      GtkTextLine *new_line;
      
      new_line = _gtk_text_line_next (real->line);
      g_assert (new_line);
      g_assert (new_line != real->line);
      g_assert (!_gtk_text_line_is_last (new_line, real->tree));
      
      real->line = new_line;

      real->line_byte_offset = 0;
      real->line_char_offset = 0;

      real->segment_byte_offset = 0;
      real->segment_char_offset = 0;

      /* Find first segments in new line */
      real->any_segment = real->line->segments;
      real->segment = real->any_segment;
      while (real->segment->char_count == 0)
        real->segment = real->segment->next;

      return TRUE;
    }
  else
    {
      /* There is no way to move forward a line; we were already at
       * the line containing the end iterator.
       * However we may not be at the end iterator itself.
       */
      
      return FALSE;
    }
}


/* The return value of this indicates WHETHER WE MOVED.
 * The return value of public functions indicates
 * (MOVEMENT OCCURRED && NEW ITER IS DEREFERENCEABLE)
 */
static gboolean
backward_line_leaving_caches_unmodified (GtkTextRealIter *real)
{
  GtkTextLine *new_line;

  new_line = _gtk_text_line_previous (real->line);

  g_assert (new_line != real->line);

  if (new_line != NULL)
    {
      real->line = new_line;

      real->line_byte_offset = 0;
      real->line_char_offset = 0;

      real->segment_byte_offset = 0;
      real->segment_char_offset = 0;

      /* Find first segments in new line */
      real->any_segment = real->line->segments;
      real->segment = real->any_segment;
      while (real->segment->char_count == 0)
        real->segment = real->segment->next;

      return TRUE;
    }
  else
    {
      /* There is no way to move backward; we were already
         at the first line. */

      /* We leave real->line as-is */

      /* Note that we didn't clamp to the start of the first line. */

      return FALSE;
    }
}

/* The return value indicates (MOVEMENT OCCURRED && NEW ITER IS
 * DEREFERENCEABLE)
 */
static gboolean
forward_char (GtkTextRealIter *real)
{
  GtkTextIter *iter = (GtkTextIter*)real;

  check_invariants ((GtkTextIter*)real);

  ensure_char_offsets (real);

  if ( (real->segment_char_offset + 1) == real->segment->char_count)
    {
      /* Need to move to the next segment; if no next segment,
         need to move to next line. */
      return _gtk_text_iter_forward_indexable_segment (iter);
    }
  else
    {
      /* Just moving within a segment. Keep byte count
         up-to-date, if it was already up-to-date. */

      g_assert (real->segment->type == &gtk_text_char_type);

      if (real->line_byte_offset >= 0)
        {
          gint bytes;
          const char * start =
            real->segment->body.chars + real->segment_byte_offset;

          bytes = g_utf8_next_char (start) - start;

          real->line_byte_offset += bytes;
          real->segment_byte_offset += bytes;

          g_assert (real->segment_byte_offset < real->segment->byte_count);
        }

      real->line_char_offset += 1;
      real->segment_char_offset += 1;

      adjust_char_index (real, 1);

      g_assert (real->segment_char_offset < real->segment->char_count);

      /* We moved into the middle of a segment, so the any_segment
         must now be the segment we're in the middle of. */
      real->any_segment = real->segment;

      check_invariants ((GtkTextIter*)real);

      if (gtk_text_iter_is_end ((GtkTextIter*)real))
        return FALSE;
      else
        return TRUE;
    }
}

gboolean
_gtk_text_iter_forward_indexable_segment (GtkTextIter *iter)
{
  /* Need to move to the next segment; if no next segment,
     need to move to next line. */
  GtkTextLineSegment *seg;
  GtkTextLineSegment *any_seg;
  GtkTextRealIter *real;
  gint chars_skipped;
  gint bytes_skipped;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (real->line_char_offset >= 0)
    {
      chars_skipped = real->segment->char_count - real->segment_char_offset;
      g_assert (chars_skipped > 0);
    }
  else
    chars_skipped = 0;

  if (real->line_byte_offset >= 0)
    {
      bytes_skipped = real->segment->byte_count - real->segment_byte_offset;
      g_assert (bytes_skipped > 0);
    }
  else
    bytes_skipped = 0;

  /* Get first segment of any kind */
  any_seg = real->segment->next;
  /* skip non-indexable segments, if any */
  seg = any_seg;
  while (seg != NULL && seg->char_count == 0)
    seg = seg->next;

  if (seg != NULL)
    {
      real->any_segment = any_seg;
      real->segment = seg;

      if (real->line_byte_offset >= 0)
        {
          g_assert (bytes_skipped > 0);
          real->segment_byte_offset = 0;
          real->line_byte_offset += bytes_skipped;
        }

      if (real->line_char_offset >= 0)
        {
          g_assert (chars_skipped > 0);
          real->segment_char_offset = 0;
          real->line_char_offset += chars_skipped;
          adjust_char_index (real, chars_skipped);
        }

      check_invariants (iter);

      return TRUE;
    }
  else
    {
      /* End of the line */
      if (forward_line_leaving_caches_unmodified (real))
        {
          adjust_line_number (real, 1);
          if (real->line_char_offset >= 0)
            adjust_char_index (real, chars_skipped);

          g_assert (real->line_byte_offset == 0);
          g_assert (real->line_char_offset == 0);
          g_assert (real->segment_byte_offset == 0);
          g_assert (real->segment_char_offset == 0);
          g_assert (gtk_text_iter_starts_line (iter));

          check_invariants (iter);

          if (gtk_text_iter_is_end (iter))
            return FALSE;
          else
            return TRUE;
        }
      else
        {
          /* End of buffer */

          g_assert (!_gtk_text_line_is_last (real->line, real->tree));
          g_assert (_gtk_text_line_contains_end_iter (real->line, real->tree));
          g_assert (gtk_text_iter_is_end (iter));
          
          check_invariants (iter);

          return FALSE;
        }
    }
}

static gboolean
at_last_indexable_segment (GtkTextRealIter *real)
{
  GtkTextLineSegment *seg;

  /* Return TRUE if there are no indexable segments after
   * this iterator.
   */

  seg = real->segment->next;
  while (seg)
    {
      if (seg->char_count > 0)
        return FALSE;
      seg = seg->next;
    }
  return TRUE;
}

/* Goes back to the start of the next segment, even if
 * we're not at the start of the current segment (always
 * ends up on a different segment if it returns TRUE)
 */
gboolean
_gtk_text_iter_backward_indexable_segment (GtkTextIter *iter)
{
  /* Move to the start of the previous segment; if no previous
   * segment, to the last segment in the previous line. This is
   * inherently a bit inefficient due to the singly-linked list and
   * tree nodes, but we can't afford the RAM for doubly-linked.
   */
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;
  GtkTextLineSegment *any_seg;
  GtkTextLineSegment *prev_seg;
  GtkTextLineSegment *prev_any_seg;
  gint bytes_skipped;
  gint chars_skipped;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  /* Find first segments in line */
  any_seg = real->line->segments;
  seg = any_seg;
  while (seg->char_count == 0)
    seg = seg->next;

  if (seg == real->segment)
    {
      /* Could probably do this case faster by hand-coding the
       * iteration.
       */

      /* We were already at the start of a line;
       * go back to the previous line.
       */
      if (gtk_text_iter_backward_line (iter))
        {
          /* Go forward to last indexable segment in line. */
          while (!at_last_indexable_segment (real))
            _gtk_text_iter_forward_indexable_segment (iter);

          check_invariants (iter);

          return TRUE;
        }
      else
        return FALSE; /* We were at the start of the first line. */
    }

  /* We must be in the middle of a line; so find the indexable
   * segment just before our current segment.
   */
  g_assert (seg != real->segment);
  while (seg != real->segment)
    {
      prev_seg = seg;
      prev_any_seg = any_seg;

      any_seg = seg->next;
      seg = any_seg;
      while (seg->char_count == 0)
        seg = seg->next;
    }

  g_assert (prev_seg != NULL);
  g_assert (prev_any_seg != NULL);
  g_assert (prev_seg->char_count > 0);

  /* We skipped the entire previous segment, plus any
   * chars we were into the current segment.
   */
  if (real->segment_byte_offset >= 0)
    bytes_skipped = prev_seg->byte_count + real->segment_byte_offset;
  else
    bytes_skipped = -1;

  if (real->segment_char_offset >= 0)
    chars_skipped = prev_seg->char_count + real->segment_char_offset;
  else
    chars_skipped = -1;

  real->segment = prev_seg;
  real->any_segment = prev_any_seg;
  real->segment_byte_offset = 0;
  real->segment_char_offset = 0;

  if (bytes_skipped >= 0)
    {
      if (real->line_byte_offset >= 0)
        {
          real->line_byte_offset -= bytes_skipped;
          g_assert (real->line_byte_offset >= 0);
        }
    }
  else
    real->line_byte_offset = -1;

  if (chars_skipped >= 0)
    {
      if (real->line_char_offset >= 0)
        {
          real->line_char_offset -= chars_skipped;
          g_assert (real->line_char_offset >= 0);
        }

      if (real->cached_char_index >= 0)
        {
          real->cached_char_index -= chars_skipped;
          g_assert (real->cached_char_index >= 0);
        }
    }
  else
    {
      real->line_char_offset = -1;
      real->cached_char_index = -1;
    }

  /* line number is unchanged. */

  check_invariants (iter);

  return TRUE;
}

/**
 * gtk_text_iter_forward_char:
 * @iter: an iterator
 *
 * Moves @iter forward by one character offset. Note that images
 * embedded in the buffer occupy 1 character slot, so
 * gtk_text_iter_forward_char () may actually move onto an image instead
 * of a character, if you have images in your buffer.  If @iter is the
 * end iterator or one character before it, @iter will now point at
 * the end iterator, and gtk_text_iter_forward_char () returns FALSE for
 * convenience when writing loops.
 *
 * Return value: whether the new position is the end iterator
 **/
gboolean
gtk_text_iter_forward_char (GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;
  else
    {
      check_invariants (iter);
      return forward_char (real);
    }
}

/**
 * gtk_text_iter_backward_char:
 * @iter: an iterator
 *
 * Moves backward by one character offset. Returns TRUE if movement
 * was possible; if @iter was the first in the buffer (character
 * offset 0), gtk_text_iter_backward_char () returns FALSE for convenience when
 * writing loops.
 *
 * Return value: whether movement was possible
 **/
gboolean
gtk_text_iter_backward_char (GtkTextIter *iter)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  check_invariants (iter);

  return gtk_text_iter_backward_chars (iter, 1);
}

/*
  Definitely we should try to linear scan as often as possible for
  movement within a single line, because we can't use the BTree to
  speed within-line searches up; for movement between lines, we would
  like to avoid the linear scan probably.

  Instead of using this constant, it might be nice to cache the line
  length in the iterator and linear scan if motion is within a single
  line.

  I guess you'd have to profile the various approaches.
*/
#define MAX_LINEAR_SCAN 150


/**
 * gtk_text_iter_forward_chars:
 * @iter: an iterator
 * @count: number of characters to move, may be negative
 *
 * Moves @count characters if possible (if @count would move past the
 * start or end of the buffer, moves to the start or end of the
 * buffer). The return value indicates whether the new position of
 * @iter is different from its original position, and dereferenceable
 * (the last iterator in the buffer is not dereferenceable). If @count
 * is 0, the function does nothing and returns FALSE.
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_forward_chars (GtkTextIter *iter, gint count)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  FIX_OVERFLOWS (count);
  
  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;
  else if (count == 0)
    return FALSE;
  else if (count < 0)
    return gtk_text_iter_backward_chars (iter, 0 - count);
  else if (count < MAX_LINEAR_SCAN)
    {
      check_invariants (iter);

      while (count > 1)
        {
          if (!forward_char (real))
            return FALSE;
          --count;
        }

      return forward_char (real);
    }
  else
    {
      gint current_char_index;
      gint new_char_index;

      check_invariants (iter);

      current_char_index = gtk_text_iter_get_offset (iter);

      if (current_char_index == _gtk_text_btree_char_count (real->tree))
        return FALSE; /* can't move forward */

      new_char_index = current_char_index + count;
      gtk_text_iter_set_offset (iter, new_char_index);

      check_invariants (iter);

      /* Return FALSE if we're on the non-dereferenceable end
       * iterator.
       */
      if (gtk_text_iter_is_end (iter))
        return FALSE;
      else
        return TRUE;
    }
}

/**
 * gtk_text_iter_backward_chars:
 * @iter: an iterator
 * @count: number of characters to move
 *
 * Moves @count characters backward, if possible (if @count would move
 * past the start or end of the buffer, moves to the start or end of
 * the buffer).  The return value indicates whether the iterator moved
 * onto a dereferenceable position; if the iterator didn't move, or
 * moved onto the end iterator, then FALSE is returned. If @count is 0,
 * the function does nothing and returns FALSE.
 *
 * Return value: whether @iter moved and is dereferenceable
 *
 **/
gboolean
gtk_text_iter_backward_chars (GtkTextIter *iter, gint count)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  FIX_OVERFLOWS (count);
  
  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;
  else if (count == 0)
    return FALSE;
  else if (count < 0)
    return gtk_text_iter_forward_chars (iter, 0 - count);

  ensure_char_offsets (real);
  check_invariants (iter);

  if (count <= real->segment_char_offset)
    {
      /* Optimize the within-segment case */
      g_assert (real->segment->char_count > 0);
      g_assert (real->segment->type == &gtk_text_char_type);

      real->segment_char_offset -= count;
      g_assert (real->segment_char_offset >= 0);

      if (real->line_byte_offset >= 0)
        {
          gint new_byte_offset;
          gint i;

          new_byte_offset = 0;
          i = 0;
          while (i < real->segment_char_offset)
            {
              const char * start = real->segment->body.chars + new_byte_offset;
              new_byte_offset += g_utf8_next_char (start) - start;

              ++i;
            }

          real->line_byte_offset -= (real->segment_byte_offset - new_byte_offset);
          real->segment_byte_offset = new_byte_offset;
        }

      real->line_char_offset -= count;

      adjust_char_index (real, 0 - count);

      check_invariants (iter);

      return TRUE;
    }
  else
    {
      /* We need to go back into previous segments. For now,
       * just keep this really simple. FIXME
       * use backward_indexable_segment.
       */
      if (TRUE || count > MAX_LINEAR_SCAN)
        {
          gint current_char_index;
          gint new_char_index;

          current_char_index = gtk_text_iter_get_offset (iter);

          if (current_char_index == 0)
            return FALSE; /* can't move backward */

          new_char_index = current_char_index - count;
          if (new_char_index < 0)
            new_char_index = 0;
          gtk_text_iter_set_offset (iter, new_char_index);

          check_invariants (iter);

          return TRUE;
        }
      else
        {
          /* FIXME backward_indexable_segment here */

          return FALSE;
        }
    }
}

#if 0

/* These two can't be implemented efficiently (always have to use
 * a linear scan, since that's the only way to find all the non-text
 * segments)
 */

/**
 * gtk_text_iter_forward_text_chars:
 * @iter: a #GtkTextIter
 * @count: number of chars to move
 *
 * Moves forward by @count text characters (pixbufs, widgets,
 * etc. do not count as characters for this). Equivalent to moving
 * through the results of gtk_text_iter_get_text (), rather than
 * gtk_text_iter_get_slice ().
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_forward_text_chars  (GtkTextIter *iter,
                                   gint         count)
{



}

/**
 * gtk_text_iter_forward_text_chars:
 * @iter: a #GtkTextIter
 * @count: number of chars to move
 *
 * Moves backward by @count text characters (pixbufs, widgets,
 * etc. do not count as characters for this). Equivalent to moving
 * through the results of gtk_text_iter_get_text (), rather than
 * gtk_text_iter_get_slice ().
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_backward_text_chars (GtkTextIter *iter,
                                   gint         count)
{


}
#endif

/**
 * gtk_text_iter_forward_line:
 * @iter: an iterator
 *
 * Moves @iter to the start of the next line. Returns TRUE if there
 * was a next line to move to, and FALSE if @iter was simply moved to
 * the end of the buffer and is now not dereferenceable, or if @iter was
 * already at the end of the buffer.
 *
 * Return value: whether @iter can be dereferenced
 **/
gboolean
gtk_text_iter_forward_line (GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);
  
  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (forward_line_leaving_caches_unmodified (real))
    {
      invalidate_char_index (real);
      adjust_line_number (real, 1);

      check_invariants (iter);

      if (gtk_text_iter_is_end (iter))
        return FALSE;
      else
        return TRUE;
    }
  else
    {
      /* On the last line, move to end of it */
      
      if (!gtk_text_iter_is_end (iter))
        gtk_text_iter_forward_to_end (iter);
      
      check_invariants (iter);
      return FALSE;
    }
}

/**
 * gtk_text_iter_backward_line:
 * @iter: an iterator
 *
 * Moves @iter to the start of the previous line. Returns TRUE if
 * @iter could be moved; i.e. if @iter was at character offset 0, this
 * function returns FALSE. Therefore if @iter was already on line 0,
 * but not at the start of the line, @iter is snapped to the start of
 * the line and the function returns TRUE. (Note that this implies that
 * in a loop calling this function, the line number may not change on
 * every iteration, if your first iteration is on line 0.)
 *
 * Return value: whether @iter moved
 **/
gboolean
gtk_text_iter_backward_line (GtkTextIter *iter)
{
  GtkTextLine *new_line;
  GtkTextRealIter *real;
  gboolean offset_will_change;
  gint offset;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  new_line = _gtk_text_line_previous (real->line);

  offset_will_change = FALSE;
  if (real->line_char_offset > 0)
    offset_will_change = TRUE;

  if (new_line != NULL)
    {
      real->line = new_line;

      adjust_line_number (real, -1);
    }
  else
    {
      if (!offset_will_change)
        return FALSE;
    }

  invalidate_char_index (real);

  real->line_byte_offset = 0;
  real->line_char_offset = 0;

  real->segment_byte_offset = 0;
  real->segment_char_offset = 0;

  /* Find first segment in line */
  real->any_segment = real->line->segments;
  real->segment = _gtk_text_line_byte_to_segment (real->line,
                                                 0, &offset);

  g_assert (offset == 0);

  /* Note that if we are on the first line, we snap to the start of
   * the first line and return TRUE, so TRUE means the iterator
   * changed, not that the line changed; this is maybe a bit
   * weird. I'm not sure there's an obvious right thing to do though.
   */

  check_invariants (iter);

  return TRUE;
}


/**
 * gtk_text_iter_forward_lines:
 * @iter: a #GtkTextIter
 * @count: number of lines to move forward
 *
 * Moves @count lines forward, if possible (if @count would move
 * past the start or end of the buffer, moves to the start or end of
 * the buffer).  The return value indicates whether the iterator moved
 * onto a dereferenceable position; if the iterator didn't move, or
 * moved onto the end iterator, then FALSE is returned. If @count is 0,
 * the function does nothing and returns FALSE. If @count is negative,
 * moves backward by 0 - @count lines.
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_forward_lines (GtkTextIter *iter, gint count)
{
  FIX_OVERFLOWS (count);
  
  if (count < 0)
    return gtk_text_iter_backward_lines (iter, 0 - count);
  else if (count == 0)
    return FALSE;
  else if (count == 1)
    {
      check_invariants (iter);
      return gtk_text_iter_forward_line (iter);
    }
  else
    {
      gint old_line;

      old_line = gtk_text_iter_get_line (iter);

      gtk_text_iter_set_line (iter, old_line + count);

      check_invariants (iter);

      /* return whether it moved, and is dereferenceable. */
      return
        (gtk_text_iter_get_line (iter) != old_line) &&
        !gtk_text_iter_is_end (iter);
    }
}

/**
 * gtk_text_iter_backward_lines:
 * @iter: a #GtkTextIter
 * @count: number of lines to move backward
 *
 * Moves @count lines backward, if possible (if @count would move
 * past the start or end of the buffer, moves to the start or end of
 * the buffer).  The return value indicates whether the iterator moved
 * onto a dereferenceable position; if the iterator didn't move, or
 * moved onto the end iterator, then FALSE is returned. If @count is 0,
 * the function does nothing and returns FALSE. If @count is negative,
 * moves forward by 0 - @count lines.
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_backward_lines (GtkTextIter *iter, gint count)
{
  FIX_OVERFLOWS (count);
  
  if (count < 0)
    return gtk_text_iter_forward_lines (iter, 0 - count);
  else if (count == 0)
    return FALSE;
  else if (count == 1)
    {
      return gtk_text_iter_backward_line (iter);
    }
  else
    {
      gint old_line;

      old_line = gtk_text_iter_get_line (iter);

      gtk_text_iter_set_line (iter, MAX (old_line - count, 0));

      return (gtk_text_iter_get_line (iter) != old_line);
    }
}

typedef gboolean (* FindLogAttrFunc) (const PangoLogAttr *attrs,
                                      gint                offset,
                                      gint                min_offset,
                                      gint                len,
                                      gint               *found_offset,
                                      gboolean            already_moved_initially);

typedef gboolean (* TestLogAttrFunc) (const PangoLogAttr *attrs,
                                      gint                offset,
                                      gint                min_offset,
                                      gint                len);

/* Word funcs */

static gboolean
find_word_end_func (const PangoLogAttr *attrs,
                    gint          offset,
                    gint          min_offset,
                    gint          len,
                    gint         *found_offset,
                    gboolean      already_moved_initially)
{
  if (!already_moved_initially)
    ++offset;

  /* Find end of next word */
  while (offset < min_offset + len &&
         !attrs[offset].is_word_end)
    ++offset;

  *found_offset = offset;

  return offset < min_offset + len;
}

static gboolean
is_word_end_func (const PangoLogAttr *attrs,
                  gint          offset,
                  gint          min_offset,
                  gint          len)
{
  return attrs[offset].is_word_end;
}

static gboolean
find_word_start_func (const PangoLogAttr *attrs,
                      gint          offset,
                      gint          min_offset,
                      gint          len,
                      gint         *found_offset,
                      gboolean      already_moved_initially)
{
  if (!already_moved_initially)
    --offset;

  /* Find start of prev word */
  while (offset >= min_offset &&
         !attrs[offset].is_word_start)
    --offset;

  *found_offset = offset;

  return offset >= min_offset;
}

static gboolean
is_word_start_func (const PangoLogAttr *attrs,
                    gint          offset,
                    gint          min_offset,
                    gint          len)
{
  return attrs[offset].is_word_start;
}

static gboolean
inside_word_func (const PangoLogAttr *attrs,
                  gint          offset,
                  gint          min_offset,
                  gint          len)
{
  /* Find next word start or end */
  while (offset >= min_offset &&
         !(attrs[offset].is_word_start || attrs[offset].is_word_end))
    --offset;

  return attrs[offset].is_word_start;
}

/* Sentence funcs */

static gboolean
find_sentence_end_func (const PangoLogAttr *attrs,
                        gint          offset,
                        gint          min_offset,
                        gint          len,
                        gint         *found_offset,
                        gboolean      already_moved_initially)
{
  if (!already_moved_initially)
    ++offset;

  /* Find end of next sentence */
  while (offset < min_offset + len &&
         !attrs[offset].is_sentence_end)
    ++offset;

  *found_offset = offset;

  return offset < min_offset + len;
}

static gboolean
is_sentence_end_func (const PangoLogAttr *attrs,
                      gint          offset,
                      gint          min_offset,
                      gint          len)
{
  return attrs[offset].is_sentence_end;
}

static gboolean
find_sentence_start_func (const PangoLogAttr *attrs,
                          gint          offset,
                          gint          min_offset,
                          gint          len,
                          gint         *found_offset,
                          gboolean      already_moved_initially)
{
  if (!already_moved_initially)
    --offset;

  /* Find start of prev sentence */
  while (offset >= min_offset &&
         !attrs[offset].is_sentence_start)
    --offset;

  *found_offset = offset;

  return offset >= min_offset;
}

static gboolean
is_sentence_start_func (const PangoLogAttr *attrs,
                        gint          offset,
                        gint          min_offset,
                        gint          len)
{
  return attrs[offset].is_sentence_start;
}

static gboolean
inside_sentence_func (const PangoLogAttr *attrs,
                      gint          offset,
                      gint          min_offset,
                      gint          len)
{
  /* Find next sentence start or end */
  while (offset >= min_offset &&
         !(attrs[offset].is_sentence_start || attrs[offset].is_sentence_end))
    --offset;

  return attrs[offset].is_sentence_start;
}

static gboolean
test_log_attrs (const GtkTextIter *iter,
                TestLogAttrFunc    func)
{
  gint char_len;
  const PangoLogAttr *attrs;
  int offset;
  gboolean result = FALSE;

  g_return_val_if_fail (iter != NULL, FALSE);

  attrs = _gtk_text_buffer_get_line_log_attrs (gtk_text_iter_get_buffer (iter),
                                               iter, &char_len);

  offset = gtk_text_iter_get_line_offset (iter);

  /* char_len may be 0 and attrs will be NULL if so, if
   * iter is the end iter and the last line is empty
   */
  
  if (offset < char_len)
    result = (* func) (attrs, offset, 0, char_len);

  return result;
}

static gboolean
find_line_log_attrs (const GtkTextIter *iter,
                     FindLogAttrFunc    func,
                     gint              *found_offset,
                     gboolean           already_moved_initially)
{
  gint char_len;
  const PangoLogAttr *attrs;
  int offset;
  gboolean result = FALSE;

  g_return_val_if_fail (iter != NULL, FALSE);
  
  attrs = _gtk_text_buffer_get_line_log_attrs (gtk_text_iter_get_buffer (iter),
                                               iter, &char_len);      

  offset = gtk_text_iter_get_line_offset (iter);
  
  /* char_len may be 0 and attrs will be NULL if so, if
   * iter is the end iter and the last line is empty
   */
  
  if (attrs)
    result = (* func) (attrs, offset, 0, char_len, found_offset,
                       already_moved_initially);

  return result;
}

/* FIXME this function is very, very gratuitously slow */
static gboolean
find_by_log_attrs (GtkTextIter    *iter,
                   FindLogAttrFunc func,
                   gboolean        forward,
                   gboolean        already_moved_initially)
{
  GtkTextIter orig;
  gint offset = 0;
  gboolean found = FALSE;

  g_return_val_if_fail (iter != NULL, FALSE);

  orig = *iter;
  
  found = find_line_log_attrs (iter, func, &offset, already_moved_initially);
  
  if (!found)
    {
      if (forward)
        {
          if (gtk_text_iter_forward_line (iter))
            return find_by_log_attrs (iter, func, forward,
                                      TRUE);
          else
            return FALSE;
        }
      else
        {                    
          /* go to end of previous line. need to check that
           * line is > 0 because backward_line snaps to start of
           * line 0 if it's on line 0
           */
          if (gtk_text_iter_get_line (iter) > 0 && 
              gtk_text_iter_backward_line (iter))
            {
              if (!gtk_text_iter_ends_line (iter))
                gtk_text_iter_forward_to_line_end (iter);
              
              return find_by_log_attrs (iter, func, forward,
                                        TRUE);
            }
          else
            return FALSE;
        }
    }
  else
    {      
      gtk_text_iter_set_line_offset (iter, offset);

      return
        (already_moved_initially || !gtk_text_iter_equal (iter, &orig)) &&
        !gtk_text_iter_is_end (iter);
    }
}

/**
 * gtk_text_iter_forward_word_end:
 * @iter: a #GtkTextIter
 * 
 * Moves forward to the next word end. (If @iter is currently on a
 * word end, moves forward to the next one after that.) Word breaks
 * are determined by Pango and should be correct for nearly any
 * language (if not, the correct fix would be to the Pango word break
 * algorithms).
 * 
 * Return value: %TRUE if @iter moved and is not the end iterator 
 **/
gboolean
gtk_text_iter_forward_word_end (GtkTextIter *iter)
{
  return find_by_log_attrs (iter, find_word_end_func, TRUE, FALSE);
}

/**
 * gtk_text_iter_backward_word_start:
 * @iter: a #GtkTextIter
 * 
 * Moves backward to the next word start. (If @iter is currently on a
 * word start, moves backward to the next one after that.) Word breaks
 * are determined by Pango and should be correct for nearly any
 * language (if not, the correct fix would be to the Pango word break
 * algorithms).
 * 
 * Return value: %TRUE if @iter moved and is not the end iterator 
 **/
gboolean
gtk_text_iter_backward_word_start (GtkTextIter      *iter)
{
  return find_by_log_attrs (iter, find_word_start_func, FALSE, FALSE);
}

/* FIXME a loop around a truly slow function means
 * a truly spectacularly slow function.
 */

/**
 * gtk_text_iter_forward_word_ends:
 * @iter: a #GtkTextIter
 * @count: number of times to move
 * 
 * Calls gtk_text_iter_forward_word_end() up to @count times.
 *
 * Return value: %TRUE if @iter moved and is not the end iterator 
 **/
gboolean
gtk_text_iter_forward_word_ends (GtkTextIter      *iter,
                                 gint              count)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  FIX_OVERFLOWS (count);
  
  if (count == 0)
    return FALSE;

  if (count < 0)
    return gtk_text_iter_backward_word_starts (iter, -count);

  if (!gtk_text_iter_forward_word_end (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_forward_word_end (iter))
        break;
      --count;
    }
  return TRUE;
}

/**
 * gtk_text_iter_backward_word_starts
 * @iter: a #GtkTextIter
 * @count: number of times to move
 * 
 * Calls gtk_text_iter_backward_word_starts() up to @count times.
 *
 * Return value: %TRUE if @iter moved and is not the end iterator 
 **/
gboolean
gtk_text_iter_backward_word_starts (GtkTextIter      *iter,
                                    gint               count)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  FIX_OVERFLOWS (count);
  
  if (count < 0)
    return gtk_text_iter_forward_word_ends (iter, -count);

  if (!gtk_text_iter_backward_word_start (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_backward_word_start (iter))
        break;
      --count;
    }
  return TRUE;
}

/**
 * gtk_text_iter_starts_word:
 * @iter: a #GtkTextIter
 * 
 * Determines whether @iter begins a natural-language word.  Word
 * breaks are determined by Pango and should be correct for nearly any
 * language (if not, the correct fix would be to the Pango word break
 * algorithms).
 *
 * Return value: %TRUE if @iter is at the start of a word
 **/
gboolean
gtk_text_iter_starts_word (const GtkTextIter *iter)
{
  return test_log_attrs (iter, is_word_start_func);
}

/**
 * gtk_text_iter_ends_word:
 * @iter: a #GtkTextIter
 * 
 * Determines whether @iter ends a natural-language word.  Word breaks
 * are determined by Pango and should be correct for nearly any
 * language (if not, the correct fix would be to the Pango word break
 * algorithms).
 *
 * Return value: %TRUE if @iter is at the end of a word
 **/
gboolean
gtk_text_iter_ends_word (const GtkTextIter *iter)
{
  return test_log_attrs (iter, is_word_end_func);
}

/**
 * gtk_text_iter_inside_word:
 * @iter: a #GtkTextIter
 * 
 * Determines whether @iter is inside a natural-language word (as
 * opposed to say inside some whitespace).  Word breaks are determined
 * by Pango and should be correct for nearly any language (if not, the
 * correct fix would be to the Pango word break algorithms).
 * 
 * Return value: %TRUE if @iter is inside a word
 **/
gboolean
gtk_text_iter_inside_word (const GtkTextIter *iter)
{
  return test_log_attrs (iter, inside_word_func);
}

/**
 * gtk_text_iter_starts_sentence:
 * @iter: a #GtkTextIter
 * 
 * Determines whether @iter begins a sentence.  Sentence boundaries are
 * determined by Pango and should be correct for nearly any language
 * (if not, the correct fix would be to the Pango text boundary
 * algorithms).
 * 
 * Return value: %TRUE if @iter is at the start of a sentence.
 **/
gboolean
gtk_text_iter_starts_sentence (const GtkTextIter *iter)
{
  return test_log_attrs (iter, is_sentence_start_func);
}

/**
 * gtk_text_iter_ends_sentence:
 * @iter: a #GtkTextIter
 * 
 * Determines whether @iter ends a sentence.  Sentence boundaries are
 * determined by Pango and should be correct for nearly any language
 * (if not, the correct fix would be to the Pango text boundary
 * algorithms).
 * 
 * Return value: %TRUE if @iter is at the end of a sentence.
 **/
gboolean
gtk_text_iter_ends_sentence (const GtkTextIter *iter)
{
  return test_log_attrs (iter, is_sentence_end_func);
}

/**
 * gtk_text_iter_inside_sentence:
 * @iter: a #GtkTextIter
 * 
 * Determines whether @iter is inside a sentence (as opposed to in
 * between two sentences, e.g. after a period and before the first
 * letter of the next sentence).  Sentence boundaries are determined
 * by Pango and should be correct for nearly any language (if not, the
 * correct fix would be to the Pango text boundary algorithms).
 * 
 * Return value: %TRUE if @iter is inside a sentence.
 **/
gboolean
gtk_text_iter_inside_sentence (const GtkTextIter *iter)
{
  return test_log_attrs (iter, inside_sentence_func);
}

/**
 * gtk_text_iter_forward_sentence_end:
 * @iter: a #GtkTextIter
 * 
 * Moves forward to the next sentence end. (If @iter is at the end of
 * a sentence, moves to the next end of sentence.)  Sentence
 * boundaries are determined by Pango and should be correct for nearly
 * any language (if not, the correct fix would be to the Pango text
 * boundary algorithms).
 * 
 * Return value: %TRUE if @iter moved and is not the end iterator
 **/
gboolean
gtk_text_iter_forward_sentence_end (GtkTextIter *iter)
{
  return find_by_log_attrs (iter, find_sentence_end_func, TRUE, FALSE);
}

/**
 * gtk_text_iter_backward_sentence_start:
 * @iter: a #GtkTextIter
 * 
 * Moves backward to the next sentence start; if @iter is already at
 * the start of a sentence, moves backward to the next one.  Sentence
 * boundaries are determined by Pango and should be correct for nearly
 * any language (if not, the correct fix would be to the Pango text
 * boundary algorithms).
 * 
 * Return value: %TRUE if @iter moved and is not the end iterator
 **/
gboolean
gtk_text_iter_backward_sentence_start (GtkTextIter      *iter)
{
  return find_by_log_attrs (iter, find_sentence_start_func, FALSE, FALSE);
}

/* FIXME a loop around a truly slow function means
 * a truly spectacularly slow function.
 */
/**
 * gtk_text_iter_forward_sentence_ends:
 * @iter: a #GtkTextIter
 * @count: number of sentences to move
 * 
 * Calls gtk_text_iter_forward_sentence_end() @count times (or until
 * gtk_text_iter_forward_sentence_end() returns %FALSE). If @count is
 * negative, moves backward instead of forward.
 * 
 * Return value: %TRUE if @iter moved and is not the end iterator
 **/
gboolean
gtk_text_iter_forward_sentence_ends (GtkTextIter      *iter,
                                     gint              count)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  if (count == 0)
    return FALSE;

  if (count < 0)
    return gtk_text_iter_backward_sentence_starts (iter, -count);

  if (!gtk_text_iter_forward_sentence_end (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_forward_sentence_end (iter))
        break;
      --count;
    }
  return TRUE;
}

/**
 * gtk_text_iter_backward_sentence_starts:
 * @iter: a #GtkTextIter
 * @count: number of sentences to move
 * 
 * Calls gtk_text_iter_backward_sentence_start() up to @count times,
 * or until it returns %FALSE. If @count is negative, moves forward
 * instead of backward.
 * 
 * Return value: %TRUE if @iter moved and is not the end iterator
 **/
gboolean
gtk_text_iter_backward_sentence_starts (GtkTextIter      *iter,
                                        gint               count)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  if (count < 0)
    return gtk_text_iter_forward_sentence_ends (iter, -count);

  if (!gtk_text_iter_backward_sentence_start (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_backward_sentence_start (iter))
        break;
      --count;
    }
  return TRUE;
}

static gboolean
find_forward_cursor_pos_func (const PangoLogAttr *attrs,
                              gint          offset,
                              gint          min_offset,
                              gint          len,
                              gint         *found_offset,
                              gboolean      already_moved_initially)
{
  if (!already_moved_initially)
    ++offset;

  while (offset < (min_offset + len) &&
         !attrs[offset].is_cursor_position)
    ++offset;

  *found_offset = offset;

  return offset < (min_offset + len);
}

static gboolean
find_backward_cursor_pos_func (const PangoLogAttr *attrs,
                               gint          offset,
                               gint          min_offset,
                               gint          len,
                               gint         *found_offset,
                               gboolean      already_moved_initially)
{  
  if (!already_moved_initially)
    --offset;

  while (offset > min_offset &&
         !attrs[offset].is_cursor_position)
    --offset;

  *found_offset = offset;
  
  return offset >= min_offset;
}

static gboolean
is_cursor_pos_func (const PangoLogAttr *attrs,
                    gint          offset,
                    gint          min_offset,
                    gint          len)
{
  return attrs[offset].is_cursor_position;
}

/**
 * gtk_text_iter_forward_cursor_position:
 * @iter: a #GtkTextIter
 * 
 * Moves @iter forward by a single cursor position. Cursor positions
 * are (unsurprisingly) positions where the cursor can appear. Perhaps
 * surprisingly, there may not be a cursor position between all
 * characters. The most common example for European languages would be
 * a carriage return/newline sequence. For some Unicode characters,
 * the equivalent of say the letter "a" with an accent mark will be
 * represented as two characters, first the letter then a "combining
 * mark" that causes the accent to be rendered; so the cursor can't go
 * between those two characters. See also the #PangoLogAttr structure and
 * pango_break() function.
 * 
 * Return value: %TRUE if we moved and the new position is dereferenceable
 **/
gboolean
gtk_text_iter_forward_cursor_position (GtkTextIter *iter)
{
  return find_by_log_attrs (iter, find_forward_cursor_pos_func, TRUE, FALSE);
}

/**
 * gtk_text_iter_backward_cursor_position:
 * @iter: a #GtkTextIter
 * 
 * Like gtk_text_iter_forward_cursor_position(), but moves backward.
 * 
 * Return value: %TRUE if we moved and the new position is dereferenceable
 **/
gboolean
gtk_text_iter_backward_cursor_position (GtkTextIter *iter)
{
  return find_by_log_attrs (iter, find_backward_cursor_pos_func, FALSE, FALSE);
}

/**
 * gtk_text_iter_forward_cursor_positions:
 * @iter: a #GtkTextIter
 * @count: number of positions to move
 * 
 * Moves up to @count cursor positions. See
 * gtk_text_iter_forward_cursor_position() for details.
 * 
 * Return value: %TRUE if we moved and the new position is dereferenceable
 **/
gboolean
gtk_text_iter_forward_cursor_positions (GtkTextIter *iter,
                                        gint         count)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  FIX_OVERFLOWS (count);
  
  if (count == 0)
    return FALSE;
  
  if (count < 0)
    return gtk_text_iter_backward_cursor_positions (iter, -count);
  
  if (!gtk_text_iter_forward_cursor_position (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_forward_cursor_position (iter))
        break;
      --count;
    }
  return TRUE;
}

/**
 * gtk_text_iter_backward_cursor_positions:
 * @iter: a #GtkTextIter
 * @count: number of positions to move
 *
 * Moves up to @count cursor positions. See
 * gtk_text_iter_forward_cursor_position() for details.
 * 
 * Return value: %TRUE if we moved and the new position is dereferenceable
 **/
gboolean
gtk_text_iter_backward_cursor_positions (GtkTextIter *iter,
                                         gint         count)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  FIX_OVERFLOWS (count);
  
  if (count == 0)
    return FALSE;

  if (count < 0)
    return gtk_text_iter_forward_cursor_positions (iter, -count);
  
  if (!gtk_text_iter_backward_cursor_position (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_backward_cursor_position (iter))
        break;
      --count;
    }
  return TRUE;
}

/**
 * gtk_text_iter_is_cursor_position:
 * @iter: a #GtkTextIter
 * 
 * See gtk_text_iter_forward_cursor_position() or #PangoLogAttr or
 * pango_break() for details on what a cursor position is.
 * 
 * Return value: %TRUE if the cursor can be placed at @iter
 **/
gboolean
gtk_text_iter_is_cursor_position (const GtkTextIter *iter)
{
  return test_log_attrs (iter, is_cursor_pos_func);
}

/**
 * gtk_text_iter_set_line_offset:
 * @iter: a #GtkTextIter 
 * @char_on_line: a character offset relative to the start of @iter's current line
 * 
 * Moves @iter within a line, to a new <emphasis>character</emphasis>
 * (not byte) offset. The given character offset must be less than or
 * equal to the number of characters in the line; if equal, @iter
 * moves to the start of the next line. See
 * gtk_text_iter_set_line_index() if you have a byte index rather than
 * a character offset.
 *
 **/
void
gtk_text_iter_set_line_offset (GtkTextIter *iter,
                               gint         char_on_line)
{
  GtkTextRealIter *real;
  gint chars_in_line;
  
  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;
  
  check_invariants (iter);

  chars_in_line = gtk_text_iter_get_chars_in_line (iter);

  g_return_if_fail (char_on_line <= chars_in_line);

  if (char_on_line < chars_in_line)
    iter_set_from_char_offset (real, real->line, char_on_line);
  else
    gtk_text_iter_forward_line (iter); /* set to start of next line */

  check_invariants (iter);
}

/**
 * gtk_text_iter_set_line_index:
 * @iter: a #GtkTextIter
 * @byte_on_line: a byte index relative to the start of @iter's current line
 *
 * Same as gtk_text_iter_set_line_offset(), but works with a
 * <emphasis>byte</emphasis> index. The given byte index must be at
 * the start of a character, it can't be in the middle of a UTF-8
 * encoded character.
 * 
 **/
void
gtk_text_iter_set_line_index (GtkTextIter *iter,
                              gint         byte_on_line)
{
  GtkTextRealIter *real;
  gint bytes_in_line;
  
  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  check_invariants (iter);

  bytes_in_line = gtk_text_iter_get_bytes_in_line (iter);

  g_return_if_fail (byte_on_line <= bytes_in_line);
  
  if (byte_on_line < bytes_in_line)
    iter_set_from_byte_offset (real, real->line, byte_on_line);
  else
    gtk_text_iter_forward_line (iter);

  if (real->segment->type == &gtk_text_char_type &&
      (real->segment->body.chars[real->segment_byte_offset] & 0xc0) == 0x80)
    g_warning ("%s: Incorrect byte offset %d falls in the middle of a UTF-8 "
               "character; this will crash the text buffer. "
               "Byte indexes must refer to the start of a character.",
               G_STRLOC, byte_on_line);

  check_invariants (iter);
}


/**
 * gtk_text_iter_set_visible_line_offset:
 * @iter: a #GtkTextIter
 * @char_on_line: a character offset
 * 
 * Like gtk_text_iter_set_line_offset(), but the offset is in visible
 * characters, i.e. text with a tag making it invisible is not
 * counted in the offset.
 **/
void
gtk_text_iter_set_visible_line_offset (GtkTextIter *iter,
                                       gint         char_on_line)
{
  gint chars_seen = 0;
  GtkTextIter pos;

  g_return_if_fail (iter != NULL);
  
  pos = *iter;

  /* For now we use a ludicrously slow implementation */
  while (chars_seen < char_on_line)
    {
      if (!_gtk_text_btree_char_is_invisible (&pos))
        ++chars_seen;

      if (!gtk_text_iter_forward_char (&pos))
        break;

      if (chars_seen == char_on_line)
        break;
    }
  
  if (_gtk_text_iter_get_text_line (&pos) == _gtk_text_iter_get_text_line (iter))
    *iter = pos;
  else
    gtk_text_iter_forward_line (iter);
}

static gint
bytes_in_char (GtkTextIter *iter)
{
  return g_unichar_to_utf8 (gtk_text_iter_get_char (iter), NULL);
}

/**
 * gtk_text_iter_set_visible_line_index:
 * @iter: a #GtkTextIter
 * @byte_on_line: a byte index
 * 
 * Like gtk_text_iter_set_line_index(), but the index is in visible
 * bytes, i.e. text with a tag making it invisible is not counted
 * in the index.
 **/
void
gtk_text_iter_set_visible_line_index  (GtkTextIter *iter,
                                       gint         byte_on_line)
{
  gint bytes_seen = 0;
  GtkTextIter pos;

  g_return_if_fail (iter != NULL);
  
  pos = *iter;

  /* For now we use a ludicrously slow implementation */
  while (bytes_seen < byte_on_line)
    {
      if (!_gtk_text_btree_char_is_invisible (&pos))
        bytes_seen += bytes_in_char (&pos);

      if (!gtk_text_iter_forward_char (&pos))
        break;

      if (bytes_seen >= byte_on_line)
        break;
    }

  if (bytes_seen > byte_on_line)
    g_warning ("%s: Incorrect visible byte index %d falls in the middle of a UTF-8 "
               "character; this will crash the text buffer. "
               "Byte indexes must refer to the start of a character.",
               G_STRLOC, byte_on_line);
  
  if (_gtk_text_iter_get_text_line (&pos) == _gtk_text_iter_get_text_line (iter))
    *iter = pos;
  else
    gtk_text_iter_forward_line (iter);
}

/**
 * gtk_text_iter_set_line:
 * @iter: a #GtkTextIter
 * @line_number: line number (counted from 0)
 *
 * Moves iterator @iter to the start of the line @line_number.
 * 
 **/
void
gtk_text_iter_set_line (GtkTextIter *iter,
                        gint         line_number)
{
  GtkTextLine *line;
  gint real_line;
  GtkTextRealIter *real;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  check_invariants (iter);

  line = _gtk_text_btree_get_line (real->tree, line_number, &real_line);

  iter_set_from_char_offset (real, line, 0);

  /* We might as well cache this, since we know it. */
  real->cached_line_number = real_line;

  check_invariants (iter);
}

/**
 * gtk_text_iter_set_offset:
 * @iter: a #GtkTextIter
 * @char_offset: a character number
 *
 * Sets @iter to point to @char_offset. @char_offset counts from the start
 * of the entire text buffer, starting with 0.
 * 
 **/
void
gtk_text_iter_set_offset (GtkTextIter *iter,
                          gint         char_offset)
{
  GtkTextLine *line;
  GtkTextRealIter *real;
  gint line_start;
  gint real_char_index;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  check_invariants (iter);

  if (real->cached_char_index >= 0 &&
      real->cached_char_index == char_offset)
    return;

  line = _gtk_text_btree_get_line_at_char (real->tree,
                                           char_offset,
                                           &line_start,
                                           &real_char_index);

  iter_set_from_char_offset (real, line, real_char_index - line_start);

  /* Go ahead and cache this since we have it. */
  real->cached_char_index = real_char_index;

  check_invariants (iter);
}

/**
 * gtk_text_iter_forward_to_end:
 * @iter: a #GtkTextIter
 *
 * Moves @iter forward to the "end iterator," which points one past the last
 * valid character in the buffer. gtk_text_iter_get_char() called on the
 * end iterator returns 0, which is convenient for writing loops.
 * 
 **/
void
gtk_text_iter_forward_to_end  (GtkTextIter *iter)
{
  GtkTextBuffer *buffer;
  GtkTextRealIter *real;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  buffer = _gtk_text_btree_get_buffer (real->tree);

  gtk_text_buffer_get_end_iter (buffer, iter);
}

/**
 * gtk_text_iter_forward_to_line_end:
 * @iter: a #GtkTextIter
 * 
 * Moves the iterator to point to the paragraph delimiter characters,
 * which will be either a newline, a carriage return, a carriage
 * return/newline in sequence, or the Unicode paragraph separator
 * character. If the iterator is already at the paragraph delimiter
 * characters, moves to the paragraph delimiter characters for the
 * next line.
 * 
 * Return value: %TRUE if we moved and the new location is not the end iterator
 **/
gboolean
gtk_text_iter_forward_to_line_end (GtkTextIter *iter)
{
  gint current_offset;
  gint new_offset;

  g_return_val_if_fail (iter != NULL, FALSE);

  current_offset = gtk_text_iter_get_line_offset (iter);
  /* FIXME assumption that line ends in a newline; broken */
  new_offset = gtk_text_iter_get_chars_in_line (iter) - 1;

  if (current_offset < new_offset)
    {
      /* Move to end of this line. */
      gtk_text_iter_set_line_offset (iter, new_offset);
      return TRUE;
    }
  else
    {
      /* Move to end of next line. */
      if (gtk_text_iter_forward_line (iter))
        {
          /* We don't want to move past all
           * empty lines.
           */
          if (!gtk_text_iter_ends_line (iter))
            gtk_text_iter_forward_to_line_end (iter);
          return TRUE;
        }
      else
        return FALSE;
    }
}

/**
 * gtk_text_iter_forward_to_tag_toggle:
 * @iter: a #GtkTextIter
 * @tag: a #GtkTextTag, or NULL
 *
 * Moves forward to the next toggle (on or off) of the
 * #GtkTextTag @tag, or to the next toggle of any tag if
 * @tag is NULL. If no matching tag toggles are found,
 * returns FALSE, otherwise TRUE. Does not return toggles
 * located at @iter, only toggles after @iter. Sets @iter to
 * the location of the toggle, or to the end of the buffer
 * if no toggle is found.
 *
 * Return value: whether we found a tag toggle after @iter
 **/
gboolean
gtk_text_iter_forward_to_tag_toggle (GtkTextIter *iter,
                                     GtkTextTag  *tag)
{
  GtkTextLine *next_line;
  GtkTextLine *current_line;
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  current_line = real->line;
  next_line = _gtk_text_line_next_could_contain_tag (current_line,
                                                     real->tree, tag);

  while (_gtk_text_iter_forward_indexable_segment (iter))
    {
      /* If we went forward to a line that couldn't contain a toggle
         for the tag, then skip forward to a line that could contain
         it. This potentially skips huge hunks of the tree, so we
         aren't a purely linear search. */
      if (real->line != current_line)
        {
          if (next_line == NULL)
            {
              /* End of search. Set to end of buffer. */
              _gtk_text_btree_get_end_iter (real->tree, iter);
              return FALSE;
            }

          if (real->line != next_line)
            iter_set_from_byte_offset (real, next_line, 0);

          current_line = real->line;
          next_line = _gtk_text_line_next_could_contain_tag (current_line,
                                                             real->tree,
                                                             tag);
        }

      if (gtk_text_iter_toggles_tag (iter, tag))
        {
          /* If there's a toggle here, it isn't indexable so
             any_segment can't be the indexable segment. */
          g_assert (real->any_segment != real->segment);
          return TRUE;
        }
    }

  /* Check end iterator for tags */
  if (gtk_text_iter_toggles_tag (iter, tag))
    {
      /* If there's a toggle here, it isn't indexable so
         any_segment can't be the indexable segment. */
      g_assert (real->any_segment != real->segment);
      return TRUE;
    }

  /* Reached end of buffer */
  return FALSE;
}

/**
 * gtk_text_iter_backward_to_tag_toggle:
 * @iter: a #GtkTextIter
 * @tag: a #GtkTextTag, or NULL
 *
 * Moves backward to the next toggle (on or off) of the
 * #GtkTextTag @tag, or to the next toggle of any tag if
 * @tag is NULL. If no matching tag toggles are found,
 * returns FALSE, otherwise TRUE. Does not return toggles
 * located at @iter, only toggles before @iter. Sets @iter
 * to the location of the toggle, or the start of the buffer
 * if no toggle is found.
 *
 * Return value: whether we found a tag toggle before @iter
 **/
gboolean
gtk_text_iter_backward_to_tag_toggle (GtkTextIter *iter,
                                      GtkTextTag  *tag)
{
  GtkTextLine *prev_line;
  GtkTextLine *current_line;
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  current_line = real->line;
  prev_line = _gtk_text_line_previous_could_contain_tag (current_line,
                                                        real->tree, tag);


  /* If we're at segment start, go to the previous segment;
   * if mid-segment, snap to start of current segment.
   */
  if (is_segment_start (real))
    {
      if (!_gtk_text_iter_backward_indexable_segment (iter))
        return FALSE;
    }
  else
    {
      ensure_char_offsets (real);

      if (!gtk_text_iter_backward_chars (iter, real->segment_char_offset))
        return FALSE;
    }

  do
    {
      /* If we went backward to a line that couldn't contain a toggle
       * for the tag, then skip backward further to a line that
       * could contain it. This potentially skips huge hunks of the
       * tree, so we aren't a purely linear search.
       */
      if (real->line != current_line)
        {
          if (prev_line == NULL)
            {
              /* End of search. Set to start of buffer. */
              _gtk_text_btree_get_iter_at_char (real->tree, iter, 0);
              return FALSE;
            }

          if (real->line != prev_line)
            {
              /* Set to last segment in prev_line (could do this
               * more quickly)
               */
              iter_set_from_byte_offset (real, prev_line, 0);

              while (!at_last_indexable_segment (real))
                _gtk_text_iter_forward_indexable_segment (iter);
            }

          current_line = real->line;
          prev_line = _gtk_text_line_previous_could_contain_tag (current_line,
                                                                real->tree,
                                                                tag);
        }

      if (gtk_text_iter_toggles_tag (iter, tag))
        {
          /* If there's a toggle here, it isn't indexable so
           * any_segment can't be the indexable segment.
           */
          g_assert (real->any_segment != real->segment);
          return TRUE;
        }
    }
  while (_gtk_text_iter_backward_indexable_segment (iter));

  /* Reached front of buffer */
  return FALSE;
}

static gboolean
matches_pred (GtkTextIter *iter,
              GtkTextCharPredicate pred,
              gpointer user_data)
{
  gint ch;

  ch = gtk_text_iter_get_char (iter);

  return (*pred) (ch, user_data);
}

/**
 * gtk_text_iter_forward_find_char:
 * @iter: a #GtkTextIter
 * @pred: a function to be called on each character
 * @user_data: user data for @pred
 * @limit: search limit, or %NULL for none 
 * 
 * Advances @iter, calling @pred on each character. If
 * @pred returns %TRUE, returns %TRUE and stops scanning.
 * If @pred never returns %TRUE, @iter is set to @limit if
 * @limit is non-%NULL, otherwise to the end iterator.
 * 
 * Return value: whether a match was found
 **/
gboolean
gtk_text_iter_forward_find_char (GtkTextIter         *iter,
                                 GtkTextCharPredicate pred,
                                 gpointer             user_data,
                                 const GtkTextIter   *limit)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (pred != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (iter, limit) >= 0)
    return FALSE;
  
  while ((limit == NULL ||
          !gtk_text_iter_equal (limit, iter)) &&
         gtk_text_iter_forward_char (iter))
    {      
      if (matches_pred (iter, pred, user_data))
        return TRUE;
    }

  return FALSE;
}

/**
 * gtk_text_iter_backward_find_char:
 * @iter: a #GtkTextIter
 * @pred: function to be called on each character
 * @user_data: user data for @pred
 * @limit: search limit, or %NULL for none
 * 
 * Same as gtk_text_iter_forward_find_char(), but goes backward from @iter.
 * 
 * Return value: whether a match was found
 **/
gboolean
gtk_text_iter_backward_find_char (GtkTextIter         *iter,
                                  GtkTextCharPredicate pred,
                                  gpointer             user_data,
                                  const GtkTextIter   *limit)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (pred != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (iter, limit) <= 0)
    return FALSE;
  
  while ((limit == NULL ||
          !gtk_text_iter_equal (limit, iter)) &&
         gtk_text_iter_backward_char (iter))
    {
      if (matches_pred (iter, pred, user_data))
        return TRUE;
    }

  return FALSE;
}

static void
forward_chars_with_skipping (GtkTextIter *iter,
                             gint         count,
                             gboolean     skip_invisible,
                             gboolean     skip_nontext)
{

  gint i;

  g_return_if_fail (count >= 0);

  i = count;

  while (i > 0)
    {
      gboolean ignored = FALSE;

      if (skip_nontext &&
          gtk_text_iter_get_char (iter) == GTK_TEXT_UNKNOWN_CHAR)
        ignored = TRUE;

      if (!ignored &&
          skip_invisible &&
          _gtk_text_btree_char_is_invisible (iter))
        ignored = TRUE;

      gtk_text_iter_forward_char (iter);

      if (!ignored)
        --i;
    }
}

static gboolean
lines_match (const GtkTextIter *start,
             const gchar **lines,
             gboolean visible_only,
             gboolean slice,
             GtkTextIter *match_start,
             GtkTextIter *match_end)
{
  GtkTextIter next;
  gchar *line_text;
  const gchar *found;
  gint offset;

  if (*lines == NULL || **lines == '\0')
    {
      if (match_start)
        *match_start = *start;

      if (match_end)
        *match_end = *start;
      return TRUE;
    }

  next = *start;
  gtk_text_iter_forward_line (&next);

  /* No more text in buffer, but *lines is nonempty */
  if (gtk_text_iter_equal (start, &next))
    {
      return FALSE;
    }

  if (slice)
    {
      if (visible_only)
        line_text = gtk_text_iter_get_visible_slice (start, &next);
      else
        line_text = gtk_text_iter_get_slice (start, &next);
    }
  else
    {
      if (visible_only)
        line_text = gtk_text_iter_get_visible_text (start, &next);
      else
        line_text = gtk_text_iter_get_text (start, &next);
    }

  if (match_start) /* if this is the first line we're matching */
    found = strstr (line_text, *lines);
  else
    {
      /* If it's not the first line, we have to match from the
       * start of the line.
       */
      if (strncmp (line_text, *lines, strlen (*lines)) == 0)
        found = line_text;
      else
        found = NULL;
    }

  if (found == NULL)
    {
      g_free (line_text);
      return FALSE;
    }

  /* Get offset to start of search string */
  offset = g_utf8_strlen (line_text, found - line_text);

  next = *start;

  /* If match start needs to be returned, set it to the
   * start of the search string.
   */
  if (match_start)
    {
      *match_start = next;

      forward_chars_with_skipping (match_start, offset,
                                   visible_only, !slice);
    }

  /* Go to end of search string */
  offset += g_utf8_strlen (*lines, -1);

  forward_chars_with_skipping (&next, offset,
                               visible_only, !slice);

  g_free (line_text);

  ++lines;

  if (match_end)
    *match_end = next;

  /* pass NULL for match_start, since we don't need to find the
   * start again.
   */
  return lines_match (&next, lines, visible_only, slice, NULL, match_end);
}

/* strsplit () that retains the delimiter as part of the string. */
static gchar **
strbreakup (const char *string,
            const char *delimiter,
            gint        max_tokens)
{
  GSList *string_list = NULL, *slist;
  gchar **str_array, *s;
  guint i, n = 1;

  g_return_val_if_fail (string != NULL, NULL);
  g_return_val_if_fail (delimiter != NULL, NULL);

  if (max_tokens < 1)
    max_tokens = G_MAXINT;

  s = strstr (string, delimiter);
  if (s)
    {
      guint delimiter_len = strlen (delimiter);

      do
        {
          guint len;
          gchar *new_string;

          len = s - string + delimiter_len;
          new_string = g_new (gchar, len + 1);
          strncpy (new_string, string, len);
          new_string[len] = 0;
          string_list = g_slist_prepend (string_list, new_string);
          n++;
          string = s + delimiter_len;
          s = strstr (string, delimiter);
        }
      while (--max_tokens && s);
    }
  if (*string)
    {
      n++;
      string_list = g_slist_prepend (string_list, g_strdup (string));
    }

  str_array = g_new (gchar*, n);

  i = n - 1;

  str_array[i--] = NULL;
  for (slist = string_list; slist; slist = slist->next)
    str_array[i--] = slist->data;

  g_slist_free (string_list);

  return str_array;
}

/**
 * gtk_text_iter_forward_search:
 * @iter: start of search
 * @str: a search string
 * @visible_only: if %TRUE, search only visible text
 * @slice: if %TRUE, @str contains 0xFFFC when we want to match widgets, pixbufs
 * @match_start: return location for start of match, or %NULL
 * @match_end: return location for end of match, or %NULL
 * @limit: bound for the search, or %NULL for the end of the buffer
 * 
 * Searches forward for @str. Any match is returned as the range @match_start,
 * @match_end. If you specify @visible_only or @slice, the match may have
 * invisible text, pixbufs, or child widgets interspersed in @str.
 * 
 * Return value: whether a match was found
 **/
gboolean
gtk_text_iter_forward_search (const GtkTextIter *iter,
                              const gchar       *str,
                              gboolean           visible_only,
                              gboolean           slice,
                              GtkTextIter       *match_start,
                              GtkTextIter       *match_end,
                              const GtkTextIter *limit)
{
  gchar **lines = NULL;
  GtkTextIter match;
  gboolean retval = FALSE;
  GtkTextIter search;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (str != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (iter, limit) >= 0)
    return FALSE;
  
  if (*str == '\0')
    {
      /* If we can move one char, return the empty string there */
      match = *iter;
      
      if (gtk_text_iter_forward_char (&match))
        {
          if (limit &&
              gtk_text_iter_equal (&match, limit))
            return FALSE;
          
          if (match_start)
            *match_start = match;
          if (match_end)
            *match_end = match;
          return TRUE;
        }
      else
        return FALSE;
    }

  /* locate all lines */

  lines = strbreakup (str, "\n", -1);

  search = *iter;

  do
    {
      /* This loop has an inefficient worst-case, where
       * gtk_text_iter_get_text () is called repeatedly on
       * a single line.
       */
      GtkTextIter end;

      if (limit &&
          gtk_text_iter_compare (&search, limit) >= 0)
        break;
      
      if (lines_match (&search, (const gchar**)lines,
                       visible_only, slice, &match, &end))
        {
          if (limit == NULL ||
              (limit &&
               gtk_text_iter_compare (&end, limit) < 0))
            {
              retval = TRUE;
              
              if (match_start)
                *match_start = match;
              
              if (match_end)
                *match_end = end;
            }
          
          break;
        }
    }
  while (gtk_text_iter_forward_line (&search));

  g_strfreev ((gchar**)lines);

  return retval;
}

static gboolean
vectors_equal_ignoring_trailing (gchar **vec1,
                                 gchar **vec2)
{
  /* Ignores trailing chars in vec2's last line */

  gchar **i1, **i2;

  i1 = vec1;
  i2 = vec2;

  while (*i1 && *i2)
    {
      if (strcmp (*i1, *i2) != 0)
        {
          if (*(i2 + 1) == NULL) /* if this is the last line */
            {
              gint len1 = strlen (*i1);
              gint len2 = strlen (*i2);

              if (len2 >= len1 &&
                  strncmp (*i1, *i2, len1) == 0)
                {
                  /* We matched ignoring the trailing stuff in vec2 */
                  return TRUE;
                }
              else
                {
                  return FALSE;
                }
            }
          else
            {
              return FALSE;
            }
        }
      ++i1;
      ++i2;
    }

  if (*i1 || *i2)
    {
      return FALSE;
    }
  else
    return TRUE;
}

typedef struct _LinesWindow LinesWindow;

struct _LinesWindow
{
  gint n_lines;
  gchar **lines;
  GtkTextIter first_line_start;
  GtkTextIter first_line_end;
  gboolean slice;
  gboolean visible_only;
};

static void
lines_window_init (LinesWindow       *win,
                   const GtkTextIter *start)
{
  gint i;
  GtkTextIter line_start;
  GtkTextIter line_end;

  /* If we start on line 1, there are 2 lines to search (0 and 1), so
   * n_lines can be 2.
   */
  if (gtk_text_iter_is_start (start) ||
      gtk_text_iter_get_line (start) + 1 < win->n_lines)
    {
      /* Already at the end, or not enough lines to match */
      win->lines = g_new0 (gchar*, 1);
      *win->lines = NULL;
      return;
    }

  line_start = *start;
  line_end = *start;

  /* Move to start iter to start of line */
  gtk_text_iter_set_line_offset (&line_start, 0);

  if (gtk_text_iter_equal (&line_start, &line_end))
    {
      /* we were already at the start; so go back one line */
      gtk_text_iter_backward_line (&line_start);
    }

  win->first_line_start = line_start;
  win->first_line_end = line_end;

  win->lines = g_new0 (gchar*, win->n_lines + 1);

  i = win->n_lines - 1;
  while (i >= 0)
    {
      gchar *line_text;

      if (win->slice)
        {
          if (win->visible_only)
            line_text = gtk_text_iter_get_visible_slice (&line_start, &line_end);
          else
            line_text = gtk_text_iter_get_slice (&line_start, &line_end);
        }
      else
        {
          if (win->visible_only)
            line_text = gtk_text_iter_get_visible_text (&line_start, &line_end);
          else
            line_text = gtk_text_iter_get_text (&line_start, &line_end);
        }

      win->lines[i] = line_text;

      line_end = line_start;
      gtk_text_iter_backward_line (&line_start);

      --i;
    }
}

static gboolean
lines_window_back (LinesWindow *win)
{
  GtkTextIter new_start;
  gchar *line_text;

  new_start = win->first_line_start;

  if (!gtk_text_iter_backward_line (&new_start))
    return FALSE;
  else
    {
      win->first_line_start = new_start;
      win->first_line_end = new_start;

      gtk_text_iter_forward_line (&win->first_line_end);
    }

  if (win->slice)
    {
      if (win->visible_only)
        line_text = gtk_text_iter_get_visible_slice (&win->first_line_start,
                                                     &win->first_line_end);
      else
        line_text = gtk_text_iter_get_slice (&win->first_line_start,
                                             &win->first_line_end);
    }
  else
    {
      if (win->visible_only)
        line_text = gtk_text_iter_get_visible_text (&win->first_line_start,
                                                    &win->first_line_end);
      else
        line_text = gtk_text_iter_get_text (&win->first_line_start,
                                            &win->first_line_end);
    }

  /* Move lines to make room for first line. */
  g_memmove (win->lines + 1, win->lines, win->n_lines * sizeof (gchar*));

  *win->lines = line_text;

  /* Free old last line and NULL-terminate */
  g_free (win->lines[win->n_lines]);
  win->lines[win->n_lines] = NULL;

  return TRUE;
}

static void
lines_window_free (LinesWindow *win)
{
  g_strfreev (win->lines);
}

static gchar*
my_strrstr (const gchar *haystack,
            const gchar *needle)
{
  /* FIXME GLib should have a nice implementation in it, this
   * is slow-ass crap.
   */

  gint haystack_len = strlen (haystack);
  gint needle_len = strlen (needle);
  const gchar *needle_end = needle + needle_len;
  const gchar *haystack_rend = haystack - 1;
  const gchar *needle_rend = needle - 1;
  const gchar *p;

  p = haystack + haystack_len;
  while (p != haystack)
    {
      const gchar *n = needle_end - 1;
      const gchar *s = p - 1;
      while (s != haystack_rend &&
             n != needle_rend &&
             *s == *n)
        {
          --n;
          --s;
        }

      if (n == needle_rend)
        return (gchar*)++s;

      --p;
    }

  return NULL;
}

/**
 * gtk_text_iter_backward_search:
 * @iter: a #GtkTextIter where the search begins
 * @str: search string
 * @visible_only: if %TRUE search only visible text
 * @slice: if %TRUE the search string contains 0xFFFC to match pixbufs, widgets
 * @match_start: return location for start of match, or %NULL
 * @match_end: return location for end of match, or %NULL
 * @limit: location of last possible @match_start, or %NULL for start of buffer
 * 
 * Same as gtk_text_iter_forward_search(), but moves backward.
 * 
 * Return value: whether a match was found
 **/
gboolean
gtk_text_iter_backward_search (const GtkTextIter *iter,
                               const gchar       *str,
                               gboolean           visible_only,
                               gboolean           slice,
                               GtkTextIter       *match_start,
                               GtkTextIter       *match_end,
                               const GtkTextIter *limit)
{
  gchar **lines = NULL;
  gchar **l;
  gint n_lines;
  LinesWindow win;
  gboolean retval = FALSE;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (str != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (limit, iter) > 0)
    return FALSE;
  
  if (*str == '\0')
    {
      /* If we can move one char, return the empty string there */
      GtkTextIter match = *iter;

      if (limit && gtk_text_iter_equal (limit, &match))
        return FALSE;
      
      if (gtk_text_iter_backward_char (&match))
        {
          if (match_start)
            *match_start = match;
          if (match_end)
            *match_end = match;
          return TRUE;
        }
      else
        return FALSE;
    }

  /* locate all lines */

  lines = strbreakup (str, "\n", -1);

  l = lines;
  n_lines = 0;
  while (*l)
    {
      ++n_lines;
      ++l;
    }

  win.n_lines = n_lines;
  win.slice = slice;
  win.visible_only = visible_only;

  lines_window_init (&win, iter);

  if (*win.lines == NULL)
    goto out;

  do
    {
      gchar *first_line_match;

      if (limit &&
          gtk_text_iter_compare (limit, &win.first_line_end) > 0)
        {
          /* We're now before the search limit, abort. */
          goto out;
        }
      
      /* If there are multiple lines, the first line will
       * end in '\n', so this will only match at the
       * end of the first line, which is correct.
       */
      first_line_match = my_strrstr (*win.lines, *lines);

      if (first_line_match &&
          vectors_equal_ignoring_trailing (lines + 1, win.lines + 1))
        {
          /* Match! */
          gint offset;
          GtkTextIter next;
          GtkTextIter start_tmp;
          
          /* Offset to start of search string */
          offset = g_utf8_strlen (*win.lines, first_line_match - *win.lines);

          next = win.first_line_start;
          start_tmp = next;
          forward_chars_with_skipping (&start_tmp, offset,
                                       visible_only, !slice);

          if (limit &&
              gtk_text_iter_compare (limit, &start_tmp) > 0)
            goto out; /* match was bogus */
          
          if (match_start)
            *match_start = start_tmp;

          /* Go to end of search string */
          l = lines;
          while (*l)
            {
              offset += g_utf8_strlen (*l, -1);
              ++l;
            }

          forward_chars_with_skipping (&next, offset,
                                       visible_only, !slice);

          if (match_end)
            *match_end = next;

          retval = TRUE;
          goto out;
        }
    }
  while (lines_window_back (&win));

 out:
  lines_window_free (&win);
  g_strfreev (lines);
  
  return retval;
}

/*
 * Comparisons
 */

/**
 * gtk_text_iter_equal:
 * @lhs: a #GtkTextIter
 * @rhs: another #GtkTextIter
 * 
 * Tests whether two iterators are equal, using the fastest possible
 * mechanism. This function is very fast; you can expect it to perform
 * better than e.g. getting the character offset for each iterator and
 * comparing the offsets yourself. Also, it's a bit faster than
 * gtk_text_iter_compare().
 * 
 * Return value: %TRUE if the iterators point to the same place in the buffer
 **/
gboolean
gtk_text_iter_equal (const GtkTextIter *lhs,
                     const GtkTextIter *rhs)
{
  GtkTextRealIter *real_lhs;
  GtkTextRealIter *real_rhs;

  real_lhs = (GtkTextRealIter*)lhs;
  real_rhs = (GtkTextRealIter*)rhs;

  check_invariants (lhs);
  check_invariants (rhs);

  if (real_lhs->line != real_rhs->line)
    return FALSE;
  else if (real_lhs->line_byte_offset >= 0 &&
           real_rhs->line_byte_offset >= 0)
    return real_lhs->line_byte_offset == real_rhs->line_byte_offset;
  else
    {
      /* the ensure_char_offsets () calls do nothing if the char offsets
         are already up-to-date. */
      ensure_char_offsets (real_lhs);
      ensure_char_offsets (real_rhs);
      return real_lhs->line_char_offset == real_rhs->line_char_offset;
    }
}

/**
 * gtk_text_iter_compare:
 * @lhs: a #GtkTextIter
 * @rhs: another #GtkTextIter
 * 
 * A qsort()-style function that returns negative if @lhs is less than
 * @rhs, positive if @lhs is greater than @rhs, and 0 if they're equal.
 * Ordering is in character offset order, i.e. the first character in the buffer
 * is less than the second character in the buffer.
 * 
 * Return value: -1 if @lhs is less than @rhs, 1 if @lhs is greater, 0 if they are equal
 **/
gint
gtk_text_iter_compare (const GtkTextIter *lhs,
                       const GtkTextIter *rhs)
{
  GtkTextRealIter *real_lhs;
  GtkTextRealIter *real_rhs;

  real_lhs = gtk_text_iter_make_surreal (lhs);
  real_rhs = gtk_text_iter_make_surreal (rhs);

  if (real_lhs == NULL ||
      real_rhs == NULL)
    return -1; /* why not */

  check_invariants (lhs);
  check_invariants (rhs);
  
  if (real_lhs->line == real_rhs->line)
    {
      gint left_index, right_index;

      if (real_lhs->line_byte_offset >= 0 &&
          real_rhs->line_byte_offset >= 0)
        {
          left_index = real_lhs->line_byte_offset;
          right_index = real_rhs->line_byte_offset;
        }
      else
        {
          /* the ensure_char_offsets () calls do nothing if
             the offsets are already up-to-date. */
          ensure_char_offsets (real_lhs);
          ensure_char_offsets (real_rhs);
          left_index = real_lhs->line_char_offset;
          right_index = real_rhs->line_char_offset;
        }

      if (left_index < right_index)
        return -1;
      else if (left_index > right_index)
        return 1;
      else
        return 0;
    }
  else
    {
      gint line1, line2;

      line1 = gtk_text_iter_get_line (lhs);
      line2 = gtk_text_iter_get_line (rhs);
      if (line1 < line2)
        return -1;
      else if (line1 > line2)
        return 1;
      else
        return 0;
    }
}

/**
 * gtk_text_iter_in_range:
 * @iter: a #GtkTextIter
 * @start: start of range
 * @end: end of range
 * 
 * Checks whether @iter falls in the range [@start, @end).
 * @start and @end must be in ascending order.
 * 
 * Return value: %TRUE if @iter is in the range
 **/
gboolean
gtk_text_iter_in_range (const GtkTextIter *iter,
                        const GtkTextIter *start,
                        const GtkTextIter *end)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (start != NULL, FALSE);
  g_return_val_if_fail (end != NULL, FALSE);
  g_return_val_if_fail (gtk_text_iter_compare (start, end) <= 0, FALSE);
  
  return gtk_text_iter_compare (iter, start) >= 0 &&
    gtk_text_iter_compare (iter, end) < 0;
}

/**
 * gtk_text_iter_order:
 * @first: a #GtkTextIter
 * @second: another #GtkTextIter
 *
 * Swaps the value of @first and @second if @second comes before
 * @first in the buffer. That is, ensures that @first and @second are
 * in sequence. Most text buffer functions that take a range call this
 * automatically on your behalf, so there's no real reason to call it yourself
 * in those cases. There are some exceptions, such as gtk_text_iter_in_range(),
 * that expect a pre-sorted range.
 * 
 **/
void
gtk_text_iter_order (GtkTextIter *first,
                     GtkTextIter *second)
{
  g_return_if_fail (first != NULL);
  g_return_if_fail (second != NULL);

  if (gtk_text_iter_compare (first, second) > 0)
    {
      GtkTextIter tmp;

      tmp = *first;
      *first = *second;
      *second = tmp;
    }
}

/*
 * Init iterators from the BTree
 */

void
_gtk_text_btree_get_iter_at_char (GtkTextBTree *tree,
                                  GtkTextIter *iter,
                                  gint char_index)
{
  GtkTextRealIter *real = (GtkTextRealIter*)iter;
  gint real_char_index;
  gint line_start;
  GtkTextLine *line;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  line = _gtk_text_btree_get_line_at_char (tree, char_index,
                                          &line_start, &real_char_index);

  iter_init_from_char_offset (iter, tree, line, real_char_index - line_start);

  real->cached_char_index = real_char_index;

  check_invariants (iter);
}

void
_gtk_text_btree_get_iter_at_line_char (GtkTextBTree *tree,
                                       GtkTextIter *iter,
                                       gint line_number,
                                       gint char_on_line)
{
  GtkTextRealIter *real = (GtkTextRealIter*)iter;
  GtkTextLine *line;
  gint real_line;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  line = _gtk_text_btree_get_line (tree, line_number, &real_line);
  
  iter_init_from_char_offset (iter, tree, line, char_on_line);

  /* We might as well cache this, since we know it. */
  real->cached_line_number = real_line;

  check_invariants (iter);
}

void
_gtk_text_btree_get_iter_at_line_byte (GtkTextBTree   *tree,
                                       GtkTextIter    *iter,
                                       gint            line_number,
                                       gint            byte_index)
{
  GtkTextRealIter *real = (GtkTextRealIter*)iter;
  GtkTextLine *line;
  gint real_line;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  line = _gtk_text_btree_get_line (tree, line_number, &real_line);

  iter_init_from_byte_offset (iter, tree, line, byte_index);

  /* We might as well cache this, since we know it. */
  real->cached_line_number = real_line;

  check_invariants (iter);
}

void
_gtk_text_btree_get_iter_at_line      (GtkTextBTree   *tree,
                                       GtkTextIter    *iter,
                                       GtkTextLine    *line,
                                       gint            byte_offset)
{
  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);
  g_return_if_fail (line != NULL);

  iter_init_from_byte_offset (iter, tree, line, byte_offset);

  check_invariants (iter);
}

gboolean
_gtk_text_btree_get_iter_at_first_toggle (GtkTextBTree   *tree,
                                          GtkTextIter    *iter,
                                          GtkTextTag     *tag)
{
  GtkTextLine *line;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (tree != NULL, FALSE);

  line = _gtk_text_btree_first_could_contain_tag (tree, tag);

  if (line == NULL)
    {
      /* Set iter to last in tree */
      _gtk_text_btree_get_end_iter (tree, iter);
      check_invariants (iter);
      return FALSE;
    }
  else
    {
      iter_init_from_byte_offset (iter, tree, line, 0);
      gtk_text_iter_forward_to_tag_toggle (iter, tag);
      check_invariants (iter);
      return TRUE;
    }
}

gboolean
_gtk_text_btree_get_iter_at_last_toggle  (GtkTextBTree   *tree,
                                          GtkTextIter    *iter,
                                          GtkTextTag     *tag)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (tree != NULL, FALSE);

  _gtk_text_btree_get_end_iter (tree, iter);
  gtk_text_iter_backward_to_tag_toggle (iter, tag);
  check_invariants (iter);
  
  return TRUE;
}

gboolean
_gtk_text_btree_get_iter_at_mark_name (GtkTextBTree *tree,
                                       GtkTextIter *iter,
                                       const gchar *mark_name)
{
  GtkTextMark *mark;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (tree != NULL, FALSE);

  mark = _gtk_text_btree_get_mark_by_name (tree, mark_name);

  if (mark == NULL)
    return FALSE;
  else
    {
      _gtk_text_btree_get_iter_at_mark (tree, iter, mark);
      check_invariants (iter);
      return TRUE;
    }
}

void
_gtk_text_btree_get_iter_at_mark (GtkTextBTree *tree,
                                  GtkTextIter *iter,
                                  GtkTextMark *mark)
{
  GtkTextLineSegment *seg;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);
  g_return_if_fail (GTK_IS_TEXT_MARK (mark));

  seg = mark->segment;

  iter_init_from_segment (iter, tree,
                          seg->body.mark.line, seg);
  g_assert (seg->body.mark.line == _gtk_text_iter_get_text_line (iter));
  check_invariants (iter);
}

void
_gtk_text_btree_get_iter_at_child_anchor (GtkTextBTree       *tree,
                                          GtkTextIter        *iter,
                                          GtkTextChildAnchor *anchor)
{
  GtkTextLineSegment *seg;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);
  g_return_if_fail (GTK_IS_TEXT_CHILD_ANCHOR (anchor));

  seg = anchor->segment;
  
  iter_init_from_segment (iter, tree,
                          seg->body.child.line, seg);
  g_assert (seg->body.child.line == _gtk_text_iter_get_text_line (iter));
  check_invariants (iter);
}

void
_gtk_text_btree_get_end_iter         (GtkTextBTree   *tree,
                                      GtkTextIter    *iter)
{
  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  _gtk_text_btree_get_iter_at_char (tree,
                                   iter,
                                   _gtk_text_btree_char_count (tree));
  check_invariants (iter);
}

void
_gtk_text_iter_check (const GtkTextIter *iter)
{
  const GtkTextRealIter *real = (const GtkTextRealIter*)iter;
  gint line_char_offset, line_byte_offset, seg_char_offset, seg_byte_offset;
  GtkTextLineSegment *byte_segment = NULL;
  GtkTextLineSegment *byte_any_segment = NULL;
  GtkTextLineSegment *char_segment = NULL;
  GtkTextLineSegment *char_any_segment = NULL;
  gboolean segments_updated;

  /* This function checks our class invariants for the Iter class. */

  g_assert (sizeof (GtkTextIter) == sizeof (GtkTextRealIter));

  if (real->chars_changed_stamp !=
      _gtk_text_btree_get_chars_changed_stamp (real->tree))
    g_error ("iterator check failed: invalid iterator");

  if (real->line_char_offset < 0 && real->line_byte_offset < 0)
    g_error ("iterator check failed: both char and byte offsets are invalid");

  segments_updated = (real->segments_changed_stamp ==
                      _gtk_text_btree_get_segments_changed_stamp (real->tree));

#if 0
  printf ("checking iter, segments %s updated, byte %d char %d\n",
          segments_updated ? "are" : "aren't",
          real->line_byte_offset,
          real->line_char_offset);
#endif

  if (segments_updated)
    {
      if (real->segment_char_offset < 0 && real->segment_byte_offset < 0)
        g_error ("iterator check failed: both char and byte segment offsets are invalid");

      if (real->segment->char_count == 0)
        g_error ("iterator check failed: segment is not indexable.");

      if (real->line_char_offset >= 0 && real->segment_char_offset < 0)
        g_error ("segment char offset is not properly up-to-date");

      if (real->line_byte_offset >= 0 && real->segment_byte_offset < 0)
        g_error ("segment byte offset is not properly up-to-date");

      if (real->segment_byte_offset >= 0 &&
          real->segment_byte_offset >= real->segment->byte_count)
        g_error ("segment byte offset is too large.");

      if (real->segment_char_offset >= 0 &&
          real->segment_char_offset >= real->segment->char_count)
        g_error ("segment char offset is too large.");
    }

  if (real->line_byte_offset >= 0)
    {
      _gtk_text_line_byte_locate (real->line, real->line_byte_offset,
                                  &byte_segment, &byte_any_segment,
                                  &seg_byte_offset, &line_byte_offset);

      if (line_byte_offset != real->line_byte_offset)
        g_error ("wrong byte offset was stored in iterator");

      if (segments_updated)
        {
          if (real->segment != byte_segment)
            g_error ("wrong segment was stored in iterator");

          if (real->any_segment != byte_any_segment)
            g_error ("wrong any_segment was stored in iterator");

          if (seg_byte_offset != real->segment_byte_offset)
            g_error ("wrong segment byte offset was stored in iterator");

          if (byte_segment->type == &gtk_text_char_type)
            {
              const gchar *p;
              p = byte_segment->body.chars + seg_byte_offset;
              
              if (!gtk_text_byte_begins_utf8_char (p))
                g_error ("broken iterator byte index pointed into the middle of a character");
            }
        }
    }

  if (real->line_char_offset >= 0)
    {
      _gtk_text_line_char_locate (real->line, real->line_char_offset,
                                  &char_segment, &char_any_segment,
                                  &seg_char_offset, &line_char_offset);

      if (line_char_offset != real->line_char_offset)
        g_error ("wrong char offset was stored in iterator");

      if (segments_updated)
        {          
          if (real->segment != char_segment)
            g_error ("wrong segment was stored in iterator");

          if (real->any_segment != char_any_segment)
            g_error ("wrong any_segment was stored in iterator");

          if (seg_char_offset != real->segment_char_offset)
            g_error ("wrong segment char offset was stored in iterator");

          if (char_segment->type == &gtk_text_char_type)
            {
              const gchar *p;
              p = g_utf8_offset_to_pointer (char_segment->body.chars,
                                            seg_char_offset);

              /* hmm, not likely to happen eh */
              if (!gtk_text_byte_begins_utf8_char (p))
                g_error ("broken iterator char offset pointed into the middle of a character");
            }
        }
    }

  if (real->line_char_offset >= 0 && real->line_byte_offset >= 0)
    {
      if (byte_segment != char_segment)
        g_error ("char and byte offsets did not point to the same segment");

      if (byte_any_segment != char_any_segment)
        g_error ("char and byte offsets did not point to the same any segment");

      /* Make sure the segment offsets are equivalent, if it's a char
         segment. */
      if (char_segment->type == &gtk_text_char_type)
        {
          gint byte_offset = 0;
          gint char_offset = 0;
          while (char_offset < seg_char_offset)
            {
              const char * start = char_segment->body.chars + byte_offset;
              byte_offset += g_utf8_next_char (start) - start;
              char_offset += 1;
            }

          if (byte_offset != seg_byte_offset)
            g_error ("byte offset did not correspond to char offset");

          char_offset =
            g_utf8_strlen (char_segment->body.chars, seg_byte_offset);

          if (char_offset != seg_char_offset)
            g_error ("char offset did not correspond to byte offset");

          if (!gtk_text_byte_begins_utf8_char (char_segment->body.chars + seg_byte_offset))
            g_error ("byte index for iterator does not index the start of a character");
        }
    }

  if (real->cached_line_number >= 0)
    {
      gint should_be;

      should_be = _gtk_text_line_get_number (real->line);
      if (real->cached_line_number != should_be)
        g_error ("wrong line number was cached");
    }

  if (real->cached_char_index >= 0)
    {
      if (real->line_char_offset >= 0) /* only way we can check it
                                          efficiently, not a real
                                          invariant. */
        {
          gint char_index;

          char_index = _gtk_text_line_char_index (real->line);
          char_index += real->line_char_offset;

          if (real->cached_char_index != char_index)
            g_error ("wrong char index was cached");
        }
    }

  if (_gtk_text_line_is_last (real->line, real->tree))
    g_error ("Iterator was on last line (past the end iterator)");
}