#include <limits.h>
#include <stddef.h>

int
consttime_memcmp0(const void *x, const void *y, size_t n)
{
	const unsigned char *p = x;
	const unsigned char *q = y;
	int diff = 0;
	unsigned int mask = 0;
	size_t i;

	while (0 < n--) {
		const int d = *p++ - *q++;
		unsigned int u = d;

		u |= (u >> 1);
		u |= (u >> 2);
		u |= (u >> 4);
		for (i = 8; i <= CHAR_BIT; i <<= 1)
			u |= (u >> i);
		for (i = CHAR_BIT; i < CHAR_BIT*sizeof(u); i <<= 1)
			u |= (u << i);

		diff = ((mask & diff) | (~mask & d));
		mask = ((mask & mask) | (~mask & u));
	}

	return diff;
}

int
consttime_memcmp1(const void *x, const void *y, size_t n)
{
	const unsigned char *p = x;
	const unsigned char *q = y;
	int diff = 0;
	unsigned int mask = ~(unsigned int)0;
	size_t i;

	while (0 < n--) {
		const int d = *p++ - *q++;
		unsigned int u = d;

		u |= (u >> 1);
		u |= (u >> 2);
		u |= (u >> 4);
		for (i = 8; i <= CHAR_BIT; i <<= 1)
			u |= (u >> i);
		u &= 1;

		diff = ((~mask & diff) | (mask & d));
		mask = ((~mask & mask) | (mask & (mask + u)));
	}

	return diff;
}