#include <string.h>
#include <stdint.h>

#define aliases __attribute__((__may_alias__))
#define byte_repeat(x) ((size_t)~0 / 0xff * (x))
#define word_has_zero(x) (((x) - byte_repeat(0x01)) & ~(x) & byte_repeat(0x80))
#define weak_alias(o, n) extern __typeof__(o) n __attribute__((weak, alias(#o)))

char *__stpcpy(char *restrict d, const char *restrict s)
{
	size_t aliases *wd;
	const size_t aliases *ws;

	if (((uintptr_t)d | (uintptr_t)s) & sizeof(size_t) - 1) goto bytewise;

	for (; (uintptr_t)s & sizeof(size_t) - 1 && (*d = *s); d++, s++);
	if ((uintptr_t)s & sizeof(size_t) - 1) return d;

	wd = (void *)d;
	ws = (const void *)s;
	for (; !word_has_zero(*ws); wd++, ws++) *wd = *ws;
	d = (void *)wd;
	s = (const void *)ws;

bytewise:
	for (; *d = *s; d++, s++);

	return d;
}

weak_alias(__stpcpy, stpcpy);