programming-examples/c++/Others/Random.cpp - Implementation for random number class.cpp

Random.cpp - Implementation for random number class
	
	#include "Random.h"


        static const int A = 48271;
        static const int M = 2147483647;
        static const int Q = M / A;
        static const int R = M % A;

        /**
         * Construct with initialValue for the state.
         */
        Random::Random( int initialValue )
        {
            if( initialValue < 0 )
                initialValue += M;

            state = initialValue;
            if( state == 0 )
                state = 1;
        }

        /**
         * Return a pseudorandom int, and change the
         * internal state.
         */
        int Random::randomInt( )
        {
            int tmpState = A * ( state % Q ) - R * ( state / Q );
            if( tmpState >= 0 )
                state = tmpState;
            else
                state = tmpState + M;

            return state;
        }

        /**
         * Return a pseudorandom int, and change the
         * internal state. DOES NOT WORK.
         */
        int Random::randomIntWRONG( )
        {
            return state = ( A * state ) % M;
        }

        /**
         * Return a pseudorandom double in the open range 0..1
         * and change the internal state.
         */
        double Random::random0_1( )
        {
            return (double) randomInt( ) / M;
        }

        /**
         * Return an int in the closed range [low,high], and
         * change the internal state.
         */
        int Random::randomInt( int low, int high )
        {
            double partitionSize = (double) M / ( high - low + 1 );

            return (int) ( randomInt( ) / partitionSize ) + low;
        }