#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))

int strncmp(const char *_l, const char *_r, size_t n)
{
	const unsigned char *l = (const void *)_l, *r = (const void *)_r;
	const size_t aliases *wl, aliases *wr;

	if (!n--) return 0;

	if (n < sizeof(size_t) * 3 || ((uintptr_t)l | (uintptr_t)r)
	    & sizeof(size_t) - 1) goto bytewise;

	for (; (uintptr_t)l & sizeof(size_t) - 1 && *l && *l == *r
	     ; l++, r++, n--);
	if ((uintptr_t)l & sizeof(size_t) - 1) return *l - *r;

	wl = (const void *)l;
	wr = (const void *)r;
	for (; n >= sizeof(size_t) && !word_has_zero(*wl) && *wl == *wr
	     ; wl++, wr++, n -= sizeof(size_t));
	l = (const void *)wl;
	r = (const void *)wr;

bytewise:
	for (; n && *l && *l == *r; l++, r++, n--);

	return *l - *r;
}