source: tests/zombies/string-perf/make-corpus.cfa @ fefd77a

#include <stdlib.hfa>
#include <math.h>
#include <limits.h>
#include <unistd.h>

// generate random draws from a geometric distribution of the given mean
// https://math.stackexchange.com/questions/485448/prove-the-way-to-generate-geometrically-distributed-random-numbers
static double denom;
static void initialize(int mean) {
    srand(getpid());
    double p = 1.0 / (double) mean;
    denom = log(1-p);
}
static int nextGeoRand() {
    // ret = ⌊ln(U)/ln(1−p)⌋ where U ~ U(0, 1)
    double U = (double)rand() / (double)INT_MAX;
    return 1 + (int) (log(U) / denom);
}

// write a randomly generated alphabetic string whose length is drawn from above distribution
static void emit1() {
    int lim = nextGeoRand();
    // printf("==%d\n", lim);
    for (i; lim) {
        char emit = 'a' + (rand() % ('z'-'a'));
        printf("%c", emit);
    }
    printf("\n");
}

// usage: ./make-corpus toGen mean
int main(int argc, char ** argv) {
    assert(argc == 3);

    int toGen = atoi(argv[1]);
    assert(toGen > 0);
    assert(toGen < 1000000);

    int mean = atoi(argv[2]);
    assert(mean > 0);
    assert(mean < 1000);

    initialize(mean);
    for( i; toGen ) {
        emit1();
    }
}