[转] A sample of Multiply-with-carry, a pseudo-random number generator

The following is an implementation of the CMWC algorithm in the C programming language. Also, included in the program is a sample initialization function. In this implementation the lag r=4096. The period of the resulting generator is about

.

#include <stdint.h>

#define PHI 0x9e3779b9

static uint32_t Q[4096], c = 362436;

void init_rand(uint32_t x)
{
int i;

Q[0] = x;
Q[1] = x + PHI;
Q[2] = x + PHI + PHI;

for (i = 3; i < 4096; i++)
Q[i] = Q[i - 3] ^ Q[i - 2] ^ PHI ^ i;
}

uint32_t rand_cmwc(void)
{
uint64_t t, a = 18782LL;
static uint32_t i = 4095;
uint32_t x, r = 0xfffffffe;
i = (i + 1) & 4095;
t = a * Q[i] + c;
c = (t >> 32);
x = t + c;
if (x < c) {
x++;
c++;
}
return (Q[i] = r - x);
}

Wiki Multiply-with-carry

More: RNG in CryptoSys