strlen.c

#define SYSCLIB_DISABLE_BUILTINS
#include <sysclib.h>
#include <stdint.h>
#include <limits.h>
 
#define ALIGN (sizeof(size_t))
#define ONES ((size_t)-1/UCHAR_MAX)
#define HIGHS (ONES * (UCHAR_MAX/2+1))
#define HASZERO(x) (((x)-ONES) & ~(x) & HIGHS)
 
size_t strlen(const char *s)
{
    const char *a = s;
#ifdef __GNUC__
    typedef size_t __attribute__((__may_alias__)) word;
    const word *w;
    for (; (uintptr_t)s % ALIGN; s++) if (!*s) return s-a;
    for (w = (const void *)s; !HASZERO(*w); w++);
    s = (const void *)w;
#endif
    for (; *s; s++);
    return s-a;
}