/*
 *  ======================================================================
 *  The purposes of this computer program are:
 *
 *     -- Generate family of 1000 random numbers that are uniformly
 *        distributed within the interval [0,1].
 *     -- Scale the distribution so that the numbers range [10,30].
 *     -- Compute the average/standard deviation of the scaled distribution.
 *     -- Output histogram of random no's.
 *
 *  Note : We use our function random() to generate uniformly distributed
 *         random numbers. This function only works on computers having a
 *         32-bit word architecture. 
 *
 *  Copyright (C) 1995-96 by Mark Austin and David Mazzoni.
 *                                                                     
 *  This software is provided "as is" without express or implied warranty.
 *  Permission is granted to use this software on any computer system,
 *  and to redistribute it freely, subject to the following restrictions:
 * 
 *  1. The authors are not responsible for the consequences of use of
 *     this software, even if they arise from defects in the software.
 *  2. The origin of this software must not be misrepresented, either
 *     by explicit claim or by omission.
 *  3. Altered versions must be plainly marked as such, and must not
 *     be misrepresented as being the original software.
 *  4. This notice is to remain intact.
 * 
 *  Written By : M. Austin                                        May 1995
 *  ======================================================================
 */

#include <stdio.h>
#include <math.h>

void   InitRandom( long int );
double Random();

enum { SampleSize = 1000, HistogramSize = 20 };

int main( void ) {
int iaHistogram [ HistogramSize ];
int iCount, iInterval;
float fRandomNo, fAverage, fVariance;
float fSum        = 0.0;
float fSumSquares = 0.0;

  /* [a] : Zero-out elements of histogram array */

  for(iCount = 0; iCount < HistogramSize; iCount = iCount + 1) 
      iaHistogram [ iCount ] = 0;

  /* [b] : Initialize Seed for Random Numbers */

  InitRandom((long) 12);

  /* [c] : Generate, scale, and catalogue random No's */

  for(iCount = 1; iCount <= SampleSize; iCount = iCount + 1) {

      fRandomNo = 20*Random() + 10;
      fSum += fRandomNo;
      fSumSquares += fRandomNo*fRandomNo;

      iInterval = (int) floor( fRandomNo ) - 10;
      iaHistogram [ iInterval ] += 1;
  }

  /* [d] : Standard deviation and average of scaled random no's */

  fAverage  = fSum/SampleSize;
  fVariance = fSumSquares/SampleSize - fAverage*fAverage;

  printf("** Random No -- Average            = %8.5f\n", fAverage );
  printf("**           -- Variance           = %8.5f\n", fVariance );
  printf("**           -- Standard Deviation = %8.5f\n", sqrt(fVariance) );

  /* [e] : Output histogram of random numbers */

  printf("\n");
  for(iCount = 10; iCount < 30; iCount = iCount + 1)
      printf(" %5.1f  %5d \n", (iCount + 0.5), iaHistogram[ iCount-10 ] );

}

/* 
 *  --------------------------------------------------------
 *  Random() : Generate Uniformly Distributed Random Numbers
 *  --------------------------------------------------------
 */ 

static unsigned long int liSeed = 1;

void InitRandom( long int iMySeed ) {
     liSeed = iMySeed;
}

double Random() {
long int a = 16807;
long int m = 2147483647;
long int q = 127773;
long int r = 2836;
long int tmp_seed;

	tmp_seed = a*( liSeed%q ) - r*( liSeed/q );
	if( tmp_seed >= 0 )
	    liSeed = tmp_seed;
	else
	    liSeed = tmp_seed + m;
	return( ((double) liSeed)/m );
}