catch2/include/internal/catch_random_number_generator.cpp

/*
 *  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)
 */

#include "catch_random_number_generator.h"
#include "catch_context.h"
#include "catch_run_context.h"
#include "catch_interfaces_config.h"

namespace Catch {

namespace {

#if defined(_MSC_VER)
#pragma warning(push)
#pragma warning(disable:4146) // we negate uint32 during the rotate
#endif
        // Safe rotr implementation thanks to John Regehr
        uint32_t rotate_right(uint32_t val, uint32_t count) {
            const uint32_t mask = 31;
            count &= mask;
            return (val >> count) | (val << (-count & mask));
        }

#if defined(_MSC_VER)
#pragma warning(pop)
#endif

}


    SimplePcg32::SimplePcg32(result_type seed_) {
        seed(seed_);
    }


    void SimplePcg32::seed(result_type seed_) {
        m_state = 0;
        (*this)();
        m_state += seed_;
        (*this)();
    }

    void SimplePcg32::discard(uint64_t skip) {
        // We could implement this to run in O(log n) steps, but this
        // should suffice for our use case.
        for (uint64_t s = 0; s < skip; ++s) {
            static_cast<void>((*this)());
        }
    }

    SimplePcg32::result_type SimplePcg32::operator()() {
        // prepare the output value
        const uint32_t xorshifted = static_cast<uint32_t>(((m_state >> 18u) ^ m_state) >> 27u);
        const auto output = rotate_right(xorshifted, m_state >> 59u);

        // advance state
        m_state = m_state * 6364136223846793005ULL + s_inc;

        return output;
    }

    bool operator==(SimplePcg32 const& lhs, SimplePcg32 const& rhs) {
        return lhs.m_state == rhs.m_state;
    }

    bool operator!=(SimplePcg32 const& lhs, SimplePcg32 const& rhs) {
        return lhs.m_state != rhs.m_state;
    }
}