include/internal/catch_random_number_generator.h

/*
 *  Created by Martin on 30/08/2017.
 *
 *  Distributed under the Boost Software License, Version 1.0. (See accompanying
 *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 */
#ifndef TWOBLUECUBES_CATCH_RANDOM_NUMBER_GENERATOR_H_INCLUDED
#define TWOBLUECUBES_CATCH_RANDOM_NUMBER_GENERATOR_H_INCLUDED

#include <cstdint>

namespace Catch {

    // This is a simple implementation of C++11 Uniform Random Number
    // Generator. It does not provide all operators, because Catch2
    // does not use it, but it should behave as expected inside stdlib's
    // distributions.
    // The implementation is based on the PCG family (http://pcg-random.org)
    class SimplePcg32 {
        using state_type = std::uint64_t;
    public:
        using result_type = std::uint32_t;
        static constexpr result_type (min)() {
            return 0;
        }
        static constexpr result_type (max)() {
            return static_cast<result_type>(-1);
        }

        // Provide some default initial state for the default constructor
        SimplePcg32():SimplePcg32(0xed743cc4U) {}

        explicit SimplePcg32(result_type seed_);

        void seed(result_type seed_);
        void discard(uint64_t skip);

        result_type operator()();

    private:
        friend bool operator==(SimplePcg32 const& lhs, SimplePcg32 const& rhs);
        friend bool operator!=(SimplePcg32 const& lhs, SimplePcg32 const& rhs);

        // In theory we also need operator<< and operator>>
        // In practice we do not use them, so we will skip them for now


        std::uint64_t m_state;
        // This part of the state determines which "stream" of the numbers
        // is chosen -- we take it as a constant for Catch2, so we only
        // need to deal with seeding the main state.
        // Picked by reading 8 bytes from `/dev/random` :-)
        static const std::uint64_t s_inc = (0x13ed0cc53f939476ULL << 1ULL) | 1ULL;
    };

} // end namespace Catch

#endif // TWOBLUECUBES_CATCH_RANDOM_NUMBER_GENERATOR_H_INCLUDED