mango/util/random.c

#include <kernel/util.h>

typedef uint64_t word_t;
#define STATE_SIZE 312
#define MIDDLE     156
#define INIT_SHIFT 62
#define TWIST_MASK 0xb5026f5aa96619e9
#define INIT_FACT  6364136223846793005
#define SHIFT1     29
#define MASK1      0x5555555555555555
#define SHIFT2     17
#define MASK2      0x71d67fffeda60000
#define SHIFT3     37
#define MASK3      0xfff7eee000000000
#define SHIFT4     43

#define LOWER_MASK 0x7fffffff
#define UPPER_MASK (~(word_t)LOWER_MASK)
static word_t state[STATE_SIZE];
static size_t index = STATE_SIZE + 1;

static void seed(word_t s)
{
	index = STATE_SIZE;
	state[0] = s;
	for (size_t i = 1; i < STATE_SIZE; i++) {
		state[i] = (INIT_FACT
		            * (state[i - 1] ^ (state[i - 1] >> INIT_SHIFT)))
		         + i;
	}
}

static void twist(void)
{
	for (size_t i = 0; i < STATE_SIZE; i++) {
		word_t x = (state[i] & UPPER_MASK)
		         | (state[(i + 1) % STATE_SIZE] & LOWER_MASK);
		x = (x >> 1) ^ (x & 1 ? TWIST_MASK : 0);
		state[i] = state[(i + MIDDLE) % STATE_SIZE] ^ x;
	}

	index = 0;
}

static word_t mt_random(void)
{
	if (index >= STATE_SIZE) {
		twist();
	}

	word_t y = state[index];
	y ^= (y >> SHIFT1) & MASK1;
	y ^= (y << SHIFT2) & MASK2;
	y ^= (y << SHIFT3) & MASK3;
	y ^= y >> SHIFT4;

	index++;
	return y;
}

void init_random(uint64_t seedvalue)
{
	seed(seedvalue);
}

bool fill_random(void *p, unsigned int size)
{
	unsigned char *dst = p;
	uint64_t w = mt_random();
	unsigned char *src = (unsigned char *)&w;

	for (size_t i = 0, j = 0; i < size; i++, j++) {
		dst[i] = src[j];

		if (j == (sizeof w) - 1) {
			w = mt_random();
			j = 0;
		}
	}

	return true;
}