pmmlcg.c

来自「speech signal process tools」· C语言 代码 · 共 88 行

/*
      name : pmmlcg.c
      by:    Jonathan G. Fiscus
      For:   605.412 Fall 1990

      This set of routines below implement a PMMLCG linear conguential random
      number generator given the following formula
               5                    31
      Z   =   7  *  Z          mod 2  -1
       i             (i-1)
*/
#include <util/utillib.h>

static int random_seed = 1;
static int a=16807;
static int m=0x7fffffff;
static int q=127773;
static int r=2836;

void init_seed(int new_seed, int verbose)
{
    random_seed = new_seed;
    if (verbose){
        printf("PMMLCG Initializing\n\n");
        printf("PMMLCG Parameters:\n");
        printf("    seed: %d\n",random_seed);
        printf("       a: %d\n",a);
        printf("       m: %d (%x)\n",m,m);
        printf("       q: %d\n",q);
        printf("       r: %d\n\n",r);
    }
}

float pmmlcg(void)
{
    int lo, hi, test;

    hi = random_seed / q;
    lo = random_seed % q;
    test = (a*lo) - (r*hi);
    if (test > 0)
        random_seed = test;
    else
        random_seed = test + m;
    return((float)random_seed/(float)m);
}

int pmmlcg_newseed(void)
{
    pmmlcg();
    return(random_seed);
}

int pmmlcg_seed(void)
{
    return(random_seed);
}

float exp_dist(float beta)
{
    return(-(beta*log(pmmlcg())));
}

float M_erlang(float beta, int M)
{
    float product=1.0;
    int i;

    for (i=0; i<M; i++)
        product *= pmmlcg();

    return(-(beta/(float)M) * log(product));
}

int arbitrary_discrete_rv(float *prob_list, int num_prob)
{
    float value;
    int i;

    value = pmmlcg();
    for (i=0; i<num_prob; i++)
        if (value <= prob_list[i])
            return(i);
    return(num_prob-1);
}