[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