#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>

struct rc4rand_state
{
	uint_fast8_t x, y;
	uint8_t data[256];
};

/* initialize with a seed of any size */
static void rc4rand_seed(struct rc4rand_state *st, size_t len, const void *data)
{
	unsigned i, j;
	uint_fast8_t tmp;

	for (i = 0; i < 256; i++)
		st->data[i] = i;

	for (i = j = 0; i < 256; i++) {
		j = (j + ((unsigned char *)data)[i % len] + st->data[i]) & 255;
		tmp = st->data[i];
		st->data[i] = st->data[j];
		st->data[j] = tmp;
	}
	st->x = st->y = 0;
}

/* generate an arbitrarily long sequence or pseudo-random bits */
static void rc4rand(struct rc4rand_state *st, size_t len, void *out)
{
	size_t i;
	uint_fast8_t tmp;

	for (i = 0; i < len; i++) {
		unsigned m;
		st->x = (st->x + 1) & 255;
		st->y = (st->y + st->data[st->x]) & 255;
		tmp = st->data[st->x];
		st->data[st->x] = st->data[st->y];
		st->data[st->y] = tmp;
		((unsigned char*)out)[i] =
			st->data[(st->data[st->x] + st->data[st->y]) & 255];
	}
}

/* capture 32-bits in the native byte order */
static uint32_t rc4rand32(struct rc4rand_state *st)
{
	union {
		uint32_t u;
		unsigned char c[sizeof(uint32_t)];
	} buf;
	rc4rand(st, sizeof buf, &buf);
	return buf.u;
}

/* capture 64-bits in the native byte order */
static uint64_t rc4rand64(struct rc4rand_state *st)
{
	union {
		uint64_t u;
		unsigned char c[sizeof(uint64_t)];
	} buf;
	rc4rand(st, sizeof buf, &buf);
	return buf.u;
}

/* capture 32-bits in little endian byte order */
static uint32_t rc4rand32le(struct rc4rand_state *st)
{
	unsigned char buf[4] = { 0, 0, 0, 0 };
	rc4rand(st, sizeof buf, &buf);
	return buf[0] | ((uint32_t)buf[1] << 8)
		| ((uint32_t)buf[2] << 16) | ((uint32_t)buf[3] << 24);

}

/* capture 64-bits in little endian byte order */
static uint64_t rc4rand64le(struct rc4rand_state *st)
{
	unsigned char buf[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
	rc4rand(st, sizeof buf, &buf);
	return buf[0] | ((uint64_t)buf[1] << 8)
		| ((uint64_t)buf[2] << 16) | ((uint64_t)buf[3] << 24)
		| ((uint64_t)buf[4] << 32) | ((uint64_t)buf[5] << 40)
		| ((uint64_t)buf[6] << 48) | ((uint64_t)buf[7] << 56);

}

/*** example code ***/

int main()
{
	struct rc4rand_state seed;
	int i;
	uint64_t m;
	struct timeval tv;
	gettimeofday(&tv, 0);
	rc4rand_seed(&seed, sizeof tv, &tv);
	for(i = 0; i < 20; i++) {
		m = rc4rand64le(&seed);
		printf("0x%016llx\n", m);
	}

	return 0;
}