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

     1  #define _BSD_SOURCE
     2  #include <string.h>
     3  #include <stdint.h>
     4  #include <limits.h>
     5  
     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  size_t strlcpy(char *d, const char *s, size_t n)
    12  {
    13  	char *d0 = d;
    14  	size_t *wd;
    15  
    16  	if (!n--) goto finish;
    17  #ifdef __GNUC__
    18  	typedef size_t __attribute__((__may_alias__)) word;
    19  	const word *ws;
    20  	if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
    21  		for (; ((uintptr_t)s & ALIGN) && n && (*d=*s); n--, s++, d++);
    22  		if (n && *s) {
    23  			wd=(void *)d; ws=(const void *)s;
    24  			for (; n>=sizeof(size_t) && !HASZERO(*ws);
    25  			       n-=sizeof(size_t), ws++, wd++) *wd = *ws;
    26  			d=(void *)wd; s=(const void *)ws;
    27  		}
    28  	}
    29  #endif
    30  	for (; n && (*d=*s); n--, s++, d++);
    31  	*d = 0;
    32  finish:
    33  	return d-d0 + strlen(s);
    34  }