/* University College London Dept of P&A Course in C++ 3C59 
| all rights reserved 1999 
|
| Utility: Implementation of methods of a class to generate 
|           different types of random numbers
|
|
| Author: P.Clarke 
*/


#include <stdlib.h>
#include <cmath>
#include "RanGen.h"

// Needed due to limitations os SIDE 3.1 compiler
//typedef int bool;
//#define false 0 ;
//#define true  1 ;



//------------------------
// Method to generate a uniformly distributed random number in [0,1] 

float RanGen::uniform( ) 
{
   int ran ;
   float x ;

   // Use library function to get a number in [0, RAND_MAX] 
   ran = rand() ;

   //Scale to [0,1] and make it a float
   x =  float(ran)/float(RAND_MAX) ;

   return x ;

}



//------------------------
// Method to generate a normally distributed random number based upon 
// a gaussian distribution with mean=0 and standard deviation=1
//
// Note: The distribution is curtailed at +-5 sigma for speed

float RanGen::gauss( ) 
{
 
  bool notdone = true ;
  float x, y, g ;


  while( notdone ) {

    // Generate a random x value in range in [-5,+5]
    x = (this->uniform() * 10.0 ) - 5.0 ;

    //Calc the gaussian function at at x (unormalised)
    g = exp( - x*x / 2.0 ) ;

    //Generate a random number in the range [0,max(gaussian)]
    //Since we havnt normalised the gaussian its max=1 at x=0
    y = this->uniform() * 1.0 ;

    //Test if y < g
    //If it is then we keep this value of x and so can stop, 
    //otherwise continue in the loop
    if( y < g ) notdone = false ; 
    
  }

  return x ;

}