src/string/memchr.c

   1 #include <string.h>
   2 #include <stdint.h>
   3 #include <limits.h>
   4
   5 #define SS (sizeof(size_t))
   6 #define ALIGN (sizeof(size_t)-1)
   7 #define ONES ((size_t)-1/UCHAR_MAX)
   8 #define HIGHS (ONES * (UCHAR_MAX/2+1))
   9 #define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
  10
  11 void *memchr(const void *src, int c, size_t n)
  12 {
  13         const unsigned char *s = src;
  14         c = (unsigned char)c;
  15 #ifdef __GNUC__
  16         for (; ((uintptr_t)s & ALIGN) && n && *s != c; s++, n--);
  17         if (n && *s != c) {
  18                 typedef size_t __attribute__((__may_alias__)) word;
  19                 const word *w;
  20                 size_t k = ONES * c;
  21                 for (w = (const void *)s; n>=SS && !HASZERO(*w^k); w++, n-=SS);
  22                 s = (const void *)w;
  23         }
  24 #endif
  25         for (; n && *s != c; s++, n--);
  26         return n ? (void *)s : 0;
  27 }