WSJT-X/map65/libm65/gran.c

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

/* Generate gaussian random float with mean=0 and std_dev=1 */
float gran_()
{
  float fac,rsq,v1,v2;
  static float gset;
  static int iset;

  if(iset){
    /* Already got one */
    iset = 0;
    return gset;
  }
  /* Generate two evenly distributed numbers between -1 and +1
   * that are inside the unit circle
   */
  do {
    v1 = 2.0 * (float)rand() / RAND_MAX - 1;
    v2 = 2.0 * (float)rand() / RAND_MAX - 1;
    rsq = v1*v1 + v2*v2;
  } while(rsq >= 1.0 || rsq == 0.0);
  fac = sqrt(-2.0*log(rsq)/rsq);
  gset = v1*fac;
  iset++;
  return v2*fac;
}