Reduce the number of expensive division instructions done by _parse_integer()

[~andy/linux] / lib / kstrtox.c

diff --git a/lib/kstrtox.c b/lib/kstrtox.c
index 7a94c8f14e295faaa2a80958081f961dba6561ce..b1dd3e7d88cb8b1379d6bdde8b130034ce5e36ac 100644 (file)
--- a/lib/kstrtox.c
+++ b/lib/kstrtox.c
@@ -44,12 +44,13 @@ const char *_parse_integer_fixup_radix(const char *s, unsigned int *base)
  *
  * Don't you dare use this function.
  */
-unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *res)
+unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *p)
 {
+       unsigned long long res;
        unsigned int rv;
        int overflow;
 
-       *res = 0;
+       res = 0;
        rv = 0;
        overflow = 0;
        while (*s) {
@@ -64,12 +65,19 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
 
                if (val >= base)
                        break;
-               if (*res > div_u64(ULLONG_MAX - val, base))
-                       overflow = 1;
-               *res = *res * base + val;
+               /*
+                * Check for overflow only if we are within range of
+                * it in the max base we support (16)
+                */
+               if (unlikely(res & (~0ull << 60))) {
+                       if (res > div_u64(ULLONG_MAX - val, base))
+                               overflow = 1;
+               }
+               res = res * base + val;
                rv++;
                s++;
        }
+       *p = res;
        if (overflow)
                rv |= KSTRTOX_OVERFLOW;
        return rv;