RandomGenerator.cpp

/*-----------------------------------------------------------------------------------------------
The MIT License (MIT)

Copyright (c) 2014-2016 Kim Kulling

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this software and associated documentation files (the "Software"), to deal in
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
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-----------------------------------------------------------------------------------------------*/
#include <cppcore/Random/RandomGenerator.h>

#include <stdlib.h>
#include <time.h>
#include <cassert>

namespace CPPCore {

static const unsigned int N = 624;
static const unsigned int M = 397;

static void mersenne_twister_vector_init( unsigned int *seedPoints, size_t len ) {
    assert( nullptr != seedPoints );

    const unsigned int mult = 1812433253ul;
    unsigned int       seed = 5489ul;
    for (unsigned int i = 0; i < len; ++i) {
        seedPoints[ i ] = seed;
        seed = mult * (seed ^ (seed >> 30)) + (i + 1);
    }
}

static void mersenne_twister_vector_update(unsigned int* const p) {
    static const unsigned int A[ 2 ] = { 0, 0x9908B0DF };
    unsigned int i=0;
    for (; i < N - M; i++)
        p[i] = p[i + (M)] ^ (((p[i] & 0x80000000) | (p[i + 1] & 0x7FFFFFFF)) >> 1) ^ A[p[i + 1] & 1];
    for (; i < N - 1; i++)
        p[i] = p[i + (M - N)] ^ (((p[i] & 0x80000000) | (p[i + 1] & 0x7FFFFFFF)) >> 1) ^ A[p[i + 1] & 1];
    p[N - 1] = p[M - 1] ^ (((p[N - 1] & 0x80000000) | (p[0] & 0x7FFFFFFF)) >> 1) ^ A[p[0] & 1];
}

unsigned int mersenne_twister() {
    // State-vector
    static unsigned int  vector[ N ];   
    // readout index
    static int           idx = N + 1;

    if (static_cast<unsigned int>(idx) >= N) {
        if (static_cast<unsigned int>(idx) > N) {
            mersenne_twister_vector_init(vector, N);
        }
        mersenne_twister_vector_update(vector);
        idx = 0;
    }
    unsigned int e = vector[ idx++ ];
    
    // Tempering
    e ^= (e >> 11);             
    e ^= (e << 7)  & 0x9D2C5680;
    e ^= (e << 15) & 0xEFC60000;
    e ^= (e >> 18);

    return e;
}

RandomGenerator::RandomGenerator( GeneratorType type ) noexcept
: m_type( type ) {
    ::srand( static_cast< unsigned int >( time( NULL ) ) );
}

RandomGenerator::~RandomGenerator() {
    // empty
}

int RandomGenerator::get( int lower, int upper ) {
    int ret( 0 );
    if ( GeneratorType::Standard == m_type ) {
        ret = ::rand() % upper + lower;
    } else if (GeneratorType::MersenneTwister == m_type) {
        ret = mersenne_twister() % upper + lower;
    }

    return ret;
}

} // Namespace CPPCore