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

#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)))

void *__memrchr(const void *_s, int i, size_t n)
{
	i = (unsigned char )i;
	const unsigned char *s = _s;
	const size_t wi = byte_repeat(i);

	if (n < sizeof(size_t) * 3) goto bytewise;

	for (; (uintptr_t)(s + n) & sizeof(size_t) - 1 && s[n - 1] != i; n--);
	if ((uintptr_t)(s + n) & sizeof(size_t) - 1) return (void *)(s + n - 1);

	for (; n >= sizeof(size_t) &&
	       !word_has_zero(*(size_t *)(s + n - sizeof(size_t)) ^ wi)
	     ; n -= sizeof(size_t));

bytewise:
	for (; n && s[n - 1] != i; n--);

	return n ? (void *)(s + n - 1) : 0;
}

weak_alias(__memrchr, memrchr);