strchrnul.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)
 
char *__strchrnul(const char *s, int c)
{
    c = (unsigned char)c;
    if (!c) return (char *)s + strlen(s);
 
#ifdef __GNUC__
    typedef size_t __attribute__((__may_alias__)) word;
    const word *w;
    for (; (uintptr_t)s % ALIGN; s++)
        if (!*s || *(unsigned char *)s == c) return (char *)s;
    size_t k = ONES * c;
    for (w = (void *)s; !HASZERO(*w) && !HASZERO(*w^k); w++);
    s = (void *)w;
#endif
    for (; *s && *(unsigned char *)s != c; s++);
    return (char *)s;
}