/*************************************************************************
 *
 * HTCd - Copyright (C) 1998-2006 Henrik Rydberg
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

#include <mt/random.h>
#include <mt/mlock.h>
#include <time.h>

//////////////////////////////////////////////////////
//
// This file implements some routines from NumRec
//

const int NTAB=32; // NOTE: change in header if changing this

const int IA=16807;
const int IM=2147483647;
const float AM=1/float(IM);
const int IQ=127773;
const int IR=2836;
const int NDIV=1+(IM-1)/NTAB;
const float EPS=1.2e-7;
const float RNMX=1-EPS;

static int idum,iy,iv[32],flag;
static float extra;
static int inited;
static mutex_t mutex;

unsigned long RandomInit(unsigned long seed)
{
  inited=1;
  idum=seed?seed:1;
  for(int j=NTAB+7;j>=0;j--) {
    int k=idum/IQ;
    idum=IA*(idum-k*IQ)-IR*k;
    if(idum<0) idum+=IM;
    if(j<NTAB) iv[j]=idum;
  }
  iy=iv[0];
  return seed;
}

float Uniform()
{
  MLOCK(mutex);
  if(!inited) RandomInit(time(0));
  int k=idum/IQ;
  idum=IA*(idum-k*IQ)-IR*k;
  if(idum<0) idum+=IM;
  int j=iy/NDIV;
  iy=iv[j];
  iv[j]=idum;
  float temp=AM*iy; if(temp>RNMX) temp=RNMX;
  return temp;
}

float Exponential()
{
  return -log(Uniform());
}

float Gaussian()
{
  MLOCK(mutex);
  float v1,v2,rsq;
  if(flag) {
    flag=0;
    return extra;
  } else {
    do {
      v1=2*Uniform()-1;
      v2=2*Uniform()-1;
      rsq=v1*v1+v2*v2;
    } while(rsq>=1||rsq<=0);
    float fac=sqrt(-2*log(rsq)/rsq);
    flag=1; extra=v1*fac;
    return v2*fac;
  }
}