/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */

/*

 * This file is part of the LibreOffice project.

 *

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/.

 *

 * Contributor(s):

 *   Copyright (C) 2012 Tino Kluge <tino.kluge@hrz.tu-chemnitz.de>

 */

#include <comphelper/random.hxx>

#include <assert.h>

#include <stdlib.h>

#include <time.h>

#include <mutex>

#include <random>

#include <rtl/random.h>

#if defined HAVE_VALGRIND_HEADERS

#include <valgrind/memcheck.h>

#endif

// this is nothing but a simple wrapper around

// the std::random generators

namespace comphelper::rng

{

// underlying random number generator

// std::mt19937 implements the Mersenne twister algorithm which

// is fast and has good statistical properties, it produces integers

// in the range of [0, 2^32-1] internally

// memory requirement: 625*sizeof(uint32_t)

// http://en.wikipedia.org/wiki/Mersenne_twister

#define STD_RNG_ALGO std::mt19937

namespace

{

struct RandomNumberGenerator

{

    std::mutex mutex;

    STD_RNG_ALGO global_rng;

    RandomNumberGenerator() { reseed(); }

    void reseed()

    {

        // make RR easier to use, breaks easily without the RNG being repeatable

        bool bRepeatable = (getenv("SAL_RAND_REPEATABLE") != nullptr) || (getenv("RR") != nullptr);

        // valgrind on some platforms (e.g.Ubuntu16.04) does not support the new Intel RDRAND instructions,

        // which leads to "Illegal Opcode" errors, so just turn off randomness.

#if defined HAVE_VALGRIND_HEADERS

        if (RUNNING_ON_VALGRIND)

            bRepeatable = true;

#endif

        if (bRepeatable)

        {

            global_rng.seed(42);

            return;

        }

        size_t seed = 0;

        if (rtl_random_getBytes(nullptr, &seed, sizeof(seed)) != rtl_Random_E_None)

            seed = 0;

        // initialises the state of the global random number generator

        // should only be called once.

        // (note, a few std::variate_generator<> (like normal) have their

        // own state which would need a reset as well to guarantee identical

        // sequence of numbers, e.g. via myrand.distribution().reset())

        global_rng.seed(seed ^ time(nullptr));

    }

};

RandomNumberGenerator& GetTheRandomNumberGenerator()

{

    static RandomNumberGenerator RANDOM;

    return RANDOM;

}

}

void reseed() { GetTheRandomNumberGenerator().reseed(); }

// uniform ints [a,b] distribution

int uniform_int_distribution(int a, int b)

{

    std::uniform_int_distribution<int> dist(a, b);

    auto& gen = GetTheRandomNumberGenerator();

    std::scoped_lock<std::mutex> g(gen.mutex);

    return dist(gen.global_rng);

}

// uniform ints [a,b] distribution

unsigned int uniform_uint_distribution(unsigned int a, unsigned int b)

{

    std::uniform_int_distribution<unsigned int> dist(a, b);

    auto& gen = GetTheRandomNumberGenerator();

    std::scoped_lock<std::mutex> g(gen.mutex);

    return dist(gen.global_rng);

}

// uniform size_t [a,b] distribution

size_t uniform_size_distribution(size_t a, size_t b)

{

    std::uniform_int_distribution<size_t> dist(a, b);

    auto& gen = GetTheRandomNumberGenerator();

    std::scoped_lock<std::mutex> g(gen.mutex);

    return dist(gen.global_rng);

}

// uniform size_t [a,b) distribution

double uniform_real_distribution(double a, double b)

{

    assert(a < b);

    std::uniform_real_distribution<double> dist(a, b);

    auto& gen = GetTheRandomNumberGenerator();

    std::scoped_lock<std::mutex> g(gen.mutex);

    return dist(gen.global_rng);

}

} // namespace

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