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simplify logic in stpcpy; avoid copying first aligned byte twice

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gcc seems to be generating identical or near-identical code for both
versions, but the newer code is more expressive of what it's doing.
This commit is contained in:
Rich Felker
2012-10-22 15:17:09 -04:00
parent 4eb4844b31
commit 838951c97e
1 changed files with 4 additions and 4 deletions
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8
src/string/stpcpy.c
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@ -4,7 +4,7 @@
#include <limits.h> #include <limits.h>
#include "libc.h" #include "libc.h"
#define ALIGN (sizeof(size_t)-1) #define ALIGN (sizeof(size_t))
#define ONES ((size_t)-1/UCHAR_MAX) #define ONES ((size_t)-1/UCHAR_MAX)
#define HIGHS (ONES * (UCHAR_MAX/2+1)) #define HIGHS (ONES * (UCHAR_MAX/2+1))
#define HASZERO(x) ((x)-ONES & ~(x) & HIGHS) #define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
@ -14,9 +14,9 @@ char *__stpcpy(char *restrict d, const char *restrict s)
size_t *wd; size_t *wd;
const size_t *ws; const size_t *ws;
if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) { if ((uintptr_t)s % ALIGN == (uintptr_t)d % ALIGN) {
for (; (*d=*s) && ((uintptr_t)s & ALIGN); s++, d++); for (; (uintptr_t)s % ALIGN; s++, d++)
if (!*s) return d; if (!(*d=*s)) return d;
wd=(void *)d; ws=(const void *)s; wd=(void *)d; ws=(const void *)s;
for (; !HASZERO(*ws); *wd++ = *ws++); for (; !HASZERO(*ws); *wd++ = *ws++);
d=(void *)wd; s=(const void *)ws; d=(void *)wd; s=(const void *)ws;