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slightly cleaner strlen, also seems to compile to better code

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testing with gcc 4.6.3 on x86, -Os, the old version does a duplicate
null byte check after the first loop. this is purely the compiler
being stupid, but the old code was also stupid and unintuitive in how
it expressed the check.
This commit is contained in:
Rich Felker 2012-09-27 16:56:33 -04:00
parent 507faa63cb
commit 3f9ff1514e
1 changed files with 4 additions and 6 deletions
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10
src/string/strlen.c
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@ -3,7 +3,7 @@
#include <stdint.h>
#include <limits.h>
#define ALIGN (sizeof(size_t)-1)
#define ALIGN (sizeof(size_t))
#define ONES ((size_t)-1/UCHAR_MAX)
#define HIGHS (ONES * (UCHAR_MAX/2+1))
#define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
@ -12,10 +12,8 @@ size_t strlen(const char *s)
{
const char *a = s;
const size_t *w;
for (; ((uintptr_t)s & ALIGN) && *s; s++);
if (*s) {
for (w = (const void *)s; !HASZERO(*w); w++);
for (s = (const void *)w; *s; s++);
}
for (; (uintptr_t)s % ALIGN; s++) if (!*s) return s-a;
for (w = (const void *)s; !HASZERO(*w); w++);
for (s = (const void *)w; *s; s++);
return s-a;
}