#include "random.h"

float random(int& seed){

  /*  Author:  Glen Cowan
      Date:    3-OCT-1997
      C++ version: 23-Aug-1999 Simon George
    
      Multiplicative linear congruential random number generator.
      The value RANDOM is uniformly distributed in [0,1].
      The first value of the input variable seed can be any large (32 bit)
      integer.  The next call to RANDOM should use the last ouput value of
      seed*.  Modulus and multiplier values according to P.L. L'Ecuyer,
      Comm. ACM 31 (1988) 742.  See also S. Brandt, "Datenanalyse",
      BI-Wissenschaftsverlag, Mannheim (1992), p. 76.
      
      NOTE:  This routine is for mainly for pedagogical purposes and simple
      applications.  For more sophisticated algorithms see e.g. the
      CERN program library (routines RANMAR, RANLUX) and reviews such as
      F. James, "A review of pseudorandom number generators",
      Comp. Phys. Comm. 60 (1990) 329.

      * C++ note: the argument is declared as int& so that it is
      passed by reference for this purpose.
  */

  const int a = 40692;           // the multiplier
  const int m = 2147483399;      // the modulus
  const int q = m/a;
  int k, r;

// The algorithm below implements seed = MOD(a*seed,m) without producing
// integer values outside [-m,m] (which would give overflow errors).

  r = m%a;
  k = seed/q;
  seed = a*(seed - k*q) - k*r;
  if (seed<0) {
    seed = seed + m;
  }
  
  return (float)seed / (float)m;
}