+/* Time Keeping Bugs Abound! */
+
+#include <stdio.h>
+
+#include "util.h"
+
+/* Helper functions */
+static int is_leap_year(year_t year)
+{
+ return (year % 400 == 0) ? 1 :
+ (year % 100 == 0) ? 0 :
+ (year % 4 == 0) ? 1 : 0;
+}
+
+static wday_t day_of_week(year_t year, month_t month, day_t day)
+{
+ static int tmp[] = {0, 3, 2, 5, 0, 3,
+ 5, 1, 4, 6, 2, 4};
+ if (month < 3)
+ year--;
+ int start = year + year / 4
+ - year / 100
+ + year / 400
+ + tmp[month];
+ return (start + day) % 7;
+}
+
+/* Time functions */
+int days_in_year(year_t year)
+{
+ return 365 + is_leap_year(year);
+}
+
+int days_in_month(year_t year, month_t month)
+{
+ static int mdays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+ int days = mdays[month];
+ if (month == FEB)
+ days += is_leap_year(year);
+ return days;
+}
+
+int weeks_in_month(year_t year, month_t month)
+{
+ int start = start_of_month(year, month);
+ int days = days_in_month(year, month);
+ return ((start + days)-1) / 7 + 1;
+}
+
+wday_t start_of_month(year_t year, month_t month)
+{
+ return day_of_week(year, month, 1);
+}
+
+/* Debug functions */
+const char *month_to_str(month_t month)
+{
+ static const char *map[] =
+ { "Jan", "Feb", "Mar", "Apr", "May", "Jun",
+ "Jul", "Aug", "Sep", "Oct", "Nov", "Dec", };
+ return map[month];
+}
+const char *month_to_string(month_t month)
+{
+ static const char *map[] =
+ { "January", "February", "March", "April",
+ "May", "June", "July", "August",
+ "September", "October", "November", "December" };
+ return map[month];
+}
+
+const char *day_to_st(wday_t day)
+{
+ static const char *map[] =
+ { "Su","Mo", "Tu", "We", "Th", "Fr", "Sa" };
+ return map[day];
+}
+const char *day_to_str(wday_t day)
+{
+ static const char *map[] =
+ { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
+ return map[day];
+}
+const char *day_to_string(wday_t day)
+{
+ static const char *map[] =
+ { "Sunday", "Monday", "Tuesday", "Wednesday",
+ "Thursday", "Friday", "Saturday" };
+ return map[day];
+}
+
+/* Test functions */
+void test_time(void)
+{
+ printf("Year Month Start Weeks Days\n");
+ for (int y = 2012; y <= 2012; y++)
+ for (int m = JAN; m <= DEC; m++) {
+ printf("%-5d", y);
+ printf("%-10s", month_to_string(m));
+ printf("%-6s", day_to_str(start_of_month(y,m)));
+ printf("%-6d", weeks_in_month(y,m));
+ printf("%-2d", days_in_month(y,m));
+ printf("\n");
+ }
+}