--fast

[ianfhunter]

https://mathworld.wolfram.com/Dice.html

Sacrifice accuracy for speed by sampling on a normal distribution between Mac and min of the combination of dice

[ianfhunter]

Toy Example:

Usual Method (gcc test.c; time ./a.out)

#include <stdio.h>
#include <stdlib.h>

int main() {
    int sum = 0;
    for(int i = 0; i != 1000000000; i++){
        sum += (rand() % 6) + 1;
    }
    return 0;
}

Box-Muller Method (gcc test2.c -lm; time ./a.out)

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
double random_normal(double mean, double std) { /* Box-Muller. */
    static double cached = 0.0;
    double x, y, r, res;
    if (cached == 0.0) {
        do {
            x = 2.0 * rand() / RAND_MAX - 1;
            y = 2.0 * rand() / RAND_MAX - 1;
            r = x * x + y * y;
        } while (r == 0.0 || r > 1.0);
        double d = sqrt(-2.0 * log(r) / r);
        double n1 = x * d;
        double n2 = y * d;
        res = n1 * std + mean;
        cached = n2;
    }
    else {
        res = cached * std + mean;
        cached = 0.0;
    }
    return res;
}

int main() {
   int total = 1000000000;
   float die = 6;
   float mean = (die+1)/2;
   int result = random_normal(mean, 1);
   return 0;
}

Original Time	New Time
12.643s	0.002s

TODO: Check

[ianfhunter]

Implemented in #391