stpcpy.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 *__stpcpy(char *restrict d, const char *restrict s)
{
#ifdef __GNUC__
    typedef size_t __attribute__((__may_alias__)) word;
    // cppcheck-suppress variableScope
    word *wd;
    // cppcheck-suppress variableScope
    const word *ws;
    if ((uintptr_t)s % ALIGN == (uintptr_t)d % ALIGN) {
        for (; (uintptr_t)s % ALIGN; s++, d++)
            if (!(*d=*s)) return d;
        wd=(void *)d; ws=(const void *)s;
        for (; !HASZERO(*ws); *wd++ = *ws++);
        d=(void *)wd; s=(const void *)ws;
    }
#endif
    for (; (*d=*s); s++, d++);
 
    return d;
}