memchr.c raw

   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  }
  28