libcruft-util/rand/lcg.hpp

/*
 * 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/.
 *
 * Copyright 2015-2019 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "../std.hpp"

#include <type_traits>
#include <limits>


namespace cruft::rand {
    /// linear congruential generator
    ///
    /// T: output/state type
    /// M: modulus
    /// A: multiplier
    /// C: increment
    template <typename T, T M, T A, T C>
    struct lcg {
    public:
        using result_type = T;

        static_assert (std::is_unsigned_v<T>);
        explicit lcg (T seed);

        result_type operator() (void);

        static constexpr auto min (void) { return std::numeric_limits<T>::min (); }
        static constexpr auto max (void) { return std::numeric_limits<T>::max (); }

        void discard (unsigned);

    private:
        T m_x;
    };

    // glibc: typedef lcg<u64, pow2(31), 1103515245, 12345> lcg_t;
    using lcg_t = lcg<u64,0u,6364136223846793005ul, 1ul>;
}