Utility

utility.cpp

#include "utility.h"
#include <iostream>
#include <ctime>
#include <cstdlib>
namespace utility {

    using namespace std;
    
    // Generate a random number between 0 and 1
    // return a uniform number in [0,1].
    double unifRand()
    {
        return rand() / double(RAND_MAX);
    }
    //
    // Generate a random number in a real interval.
    // param a one end point of the interval
    // param b the other end of the interval
    // return a inform rand numberin [a,b].
    double unifRand(double a, double b)
    {
        return (b-a)*unifRand() + a;
    }
    //
    // Generate a random integer between 1 and a given value.
    // param n the largest value 
    // return a uniform random value in [1,...,n]
    long unifRand(long n)
    {
        
        if (n < 0) n = -n;
        if (n==0) return 0;
        /* There is a slight error in that this code can produce a return value of n+1
         **
         **  return long(unifRand()*n) + 1;
         */
        //Fixed code
        long guard = (long) (unifRand() * n) +1;
        return (guard > n)? n : guard;
    }
    //Knuth method, from http://c-faq.com/lib/gaussian.html
    double gaussrand(){
	static double V1, V2, S;
	static int phase = 0;
	double X;

	if(phase == 0){
		do {
			double U1 = (double)rand() / RAND_MAX;
			double U2 = (double)rand() / RAND_MAX;
			V1 = 2 * U1 - 1;
			V2 = 2 * U2 - 1;
			S = V1 * V1 + V2 * V2;
			} while(S >= 1 || S == 0);
		X = V1 * sqrt(-2 * log(S) / S);
	} else
		X = V2 * sqrt(-2 * log(S) / S);

	phase = 1 - phase;
	return X;
    }

    //
    // Reset the random number generator with the system clock.
    void seed()
    {
        srand(time(0));
    }

}

utility.h

#pragma once

namespace utility {
    double unifRand();
    double unifRand(double a, double b);
    long unifRand(long n);
    gaussrand();
    void seed();
}