github.com/afumu/libc@v0.0.6/musl/src/string/memchr.c (about)

     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  }