正态随机分布 C++实现

#include <stdlib.h>
#include <math.h>

double gaussrand()
{
    static double V1, V2, S;
    static int phase = 0;
    double X;
    
    if ( phase == 0 ) {
        do {
            double U1 = (double)rand() / RAND_MAX;
            double U2 = (double)rand() / RAND_MAX;
            
            V1 = 2 * U1 - 1;
            V2 = 2 * U2 - 1;
            S = V1 * V1 + V2 * V2;
        } while(S >= 1 || S == 0);
        
        X = V1 * sqrt(-2 * log(S) / S);
    } else
        X = V2 * sqrt(-2 * log(S) / S);
    
    phase = 1 - phase;
    
    return X;
}