#include <math.h>
#include "genlib.h"

#define NTAB 32

double gasdev(long *idum,long *idum2, long *iy, long iv[NTAB])
/*returns a normally distributed deviate with 0 mean*/
/*and unit variance, using ran2(idum) as the source */
/*of uniform deviates                               */
{
  double ran2(long *idum,long *idum2, long *iy, long iv[NTAB]);
  static int iset = 0;
  static double gset;
  double fac,rsq,v1,v2;

    if (iset == 0) {
    do {
      v1 = 2.0*ran2(idum,idum2,iy,iv)-1.0;
      v2 = 2.0*ran2(idum,idum2,iy,iv)-1.0;
      rsq = v1*v1+v2*v2;
    } while (rsq >= 1.0 || rsq == 0.0);

    fac = sqrt(-2.0*log(rsq)/rsq);
    gset = v1*fac;
    iset = 1;
    return (v2*fac);
  } else {
    iset = 0;
    return (gset);
  }
}