\section{Rand.cpp}

<<Rand.cpp>>=
// File: Rand.ccp 
// Last Revision: 23-Mar-2001
// Description: functions for the generation of random values.

//  programmer: Romeo Rizzi.
//     rrizzi@rtm.science.unitn.it
//
//  responsible: Roberto Battiti. 
//     battiti@science.unitn.it
//
//  group:  LEA (Laboratory for Experimental Algorithmics). 
//     http://rtm.science.unitn.it/
//
// Note: The two functions myrand() and smyrand() were written by Dell'Amico
// using the portable pseudorandom generator RnG (see below).


#include "Rand.H"

#define PRANDMAX 1000000000

int dmxa, dmxb, dmxarr[55];


float myrand()
{
  return ((float)lprand()) / PRANDMAX;
}

float smyrand(int seed)
{
  return (float) sprand(seed);
}


int dado(int num_facce)
{
  return (int) (num_facce * myrand());
}


/*
    This file contains a set of c-language functions for generating
    uniform integers.   This is a COMPLETELY PORTABLE generator.
    it will give iDEnTiCAL sequences of random numbers for any
    architecture with at least 30-bit integers, regardless of the
    integer representation, MAXinT value, or roundoff/truncation
    method, etc.
    This Truly Remarkable RnG is described more fully in
    j. Bentley's column, ``The Software Exploratorium ''
    to appear in Unix Review in 1991.
    it is based on one in knuth, Vol 2, Section 3.2.2 (Algorithm A)

    This is a little driver program so you can test the code.
    Giving input parameters: 0 3 1
    should produce
       921674862
       250065336
       377506581
     Giving 1000000 1 2
     should produce
       572653995

       void main()
       {
       int i,j,n,m,seed;
       scanf("%d %d %d",&m,&n,&seed);
       i = sprand(seed);
       for(i=0; i< m;i++)
          j = lprand();
       for (i=0; i< n; i++)
          printf("\n%ld",lprand());
       }
*/


// ---------RnG---------------------
//   Returns long ints from the
//   range 0...PRANDMAX-1

int lprand()
{ 
  dmxa --;
  if (dmxa < 0) dmxa = 54;
  dmxb --;
  if (dmxb < 0) dmxb = 54;
  int t = dmxarr[dmxa] - dmxarr[dmxb];
  return dmxarr[dmxa] = ( (t < 0) ? t + PRANDMAX : t);
}


//-----------RnG initializer------------
//  Call once before using lprand

int sprand (int seed)
{
  int i, ii, last, next;
  dmxarr[0] = last = seed;
  next = 1;
  for (i=1; i< 55; i++ ) {
    ii =  21 * i % 55;
    dmxarr[ii] = next;
    next = last - next;
    if (next < 0)   next += PRANDMAX;
    last = dmxarr[ii];
  }
  dmxa = 0;
  dmxb = 24;
  for(i = 0; i<= 164; i++)
      lprand();
  return seed;
}
@