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

     1  #include <string.h>
     2  #include <stdint.h>
     3  #include <limits.h>
     4  
     5  #define ALIGN (sizeof(size_t)-1)
     6  #define ONES ((size_t)-1/UCHAR_MAX)
     7  #define HIGHS (ONES * (UCHAR_MAX/2+1))
     8  #define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
     9  
    10  void *memccpy(void *restrict dest, const void *restrict src, int c, size_t n)
    11  {
    12  	unsigned char *d = dest;
    13  	const unsigned char *s = src;
    14  
    15  	c = (unsigned char)c;
    16  #ifdef __GNUC__
    17  	typedef size_t __attribute__((__may_alias__)) word;
    18  	word *wd;
    19  	const word *ws;
    20  	if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
    21  		for (; ((uintptr_t)s & ALIGN) && n && (*d=*s)!=c; n--, s++, d++);
    22  		if ((uintptr_t)s & ALIGN) goto tail;
    23  		size_t k = ONES * c;
    24  		wd=(void *)d; ws=(const void *)s;
    25  		for (; n>=sizeof(size_t) && !HASZERO(*ws^k);
    26  		       n-=sizeof(size_t), ws++, wd++) *wd = *ws;
    27  		d=(void *)wd; s=(const void *)ws;
    28  	}
    29  #endif
    30  	for (; n && (*d=*s)!=c; n--, s++, d++);
    31  tail:
    32  	if (n) return d+1;
    33  	return 0;
    34  }