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

     1  #include <string.h>
     2  #include <stdint.h>
     3  #include <limits.h>
     4  
     5  #define ALIGN (sizeof(size_t))
     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  size_t strlen(const char *s)
    11  {
    12  	const char *a = s;
    13  #ifdef __GNUC__
    14  	typedef size_t __attribute__((__may_alias__)) word;
    15  	const word *w;
    16  	for (; (uintptr_t)s % ALIGN; s++) if (!*s) return s-a;
    17  	for (w = (const void *)s; !HASZERO(*w); w++);
    18  	s = (const void *)w;
    19  #endif
    20  	for (; *s; s++);
    21  	return s-a;
    22  }