rdrand.hpp

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//============================================================================
// vSMC/include/vsmc/rng/rdrand.hpp
//----------------------------------------------------------------------------
//                         vSMC: Scalable Monte Carlo
//----------------------------------------------------------------------------
// Copyright (c) 2013-2016, Yan Zhou
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//   Redistributions of source code must retain the above copyright notice,
//   this list of conditions and the following disclaimer.
//
//   Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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//============================================================================

#ifndef VSMC_RNG_RDRAND_HPP
#define VSMC_RNG_RDRAND_HPP

#include <vsmc/rng/internal/common.hpp>
#include <immintrin.h>

#ifndef VSMC_RNG_RDRAND_NTRIAL_MAX
#define VSMC_RNG_RDRAND_NTRIAL_MAX 0
#endif

#define VSMC_RUNTIME_WARNING_RNG_RDRAND_ENGINE_NTRIAL(ntrial, NTrialMax)      \
    VSMC_RUNTIME_WARNING((ntrial < NTrialMax),                                \
        "**RDRAND::generate** MAXIMUM NUMBER OF TRIALS EXCEEDED")

namespace vsmc
{

template <typename UIntType, std::size_t W>
inline bool rdrand(UIntType *, std::integral_constant<int, W>);

template <typename UIntType>
inline bool rdrand(UIntType *rand, std::integral_constant<int, 16>)
{
    unsigned short r;
    int cf = _rdrand16_step(&r);
    *rand = static_cast<UIntType>(r);

    return cf != 0;
}

template <typename UIntType>
inline bool rdrand(UIntType *rand, std::integral_constant<int, 32>)
{
    unsigned r;
    int cf = _rdrand32_step(&r);
    *rand = static_cast<UIntType>(r);

    return cf != 0;
}

template <typename UIntType>
inline bool rdrand(UIntType *rand, std::integral_constant<int, 64>)
{
#if defined(VSMC_MSVC) || (defined(VSMC_INTEL) && VSMC_INTEL_VERSION < 1600)
    unsigned __int64 r;
#else
    unsigned long long r;
#endif
    int cf = _rdrand64_step(&r);
    *rand = static_cast<UIntType>(r);

    return cf != 0;
}

template <typename ResultType,
    std::size_t NTrialMax = VSMC_RNG_RDRAND_NTRIAL_MAX>
class RDRANDEngine
{
    static_assert(std::is_unsigned<ResultType>::value,
        "**RDRANDEngine** USED WITH ResultType OTHER THAN UNSIGNED INTEGER "
        "TYPES");

    static_assert(std::numeric_limits<ResultType>::digits == 16 ||
            std::numeric_limits<ResultType>::digits == 32 ||
            std::numeric_limits<ResultType>::digits == 64,
        "**RDRANDEngine** USED WITH ResultType OF SIZE OTHER THAN 16, 32 OR "
        "64 BITS");

    public:
    using result_type = ResultType;

    explicit RDRANDEngine(result_type = 0) {}

    template <typename SeedSeq>
    explicit RDRANDEngine(SeedSeq &,
        typename std::enable_if<internal::is_seed_seq<SeedSeq, result_type,
            RDRANDEngine<ResultType, NTrialMax>>::value>::type * = nullptr)
    {
    }

    void seed(result_type) {}

    template <typename SeedSeq>
    void seed(SeedSeq &, typename std::enable_if<internal::is_seed_seq<SeedSeq,
                             result_type>::value>::type * = nullptr)
    {
    }

    result_type operator()()
    {
        return generate(std::integral_constant<bool, NTrialMax != 0>());
    }

    void discard(std::size_t) {}

    static constexpr result_type min()
    {
        return std::numeric_limits<result_type>::min();
    }

    static constexpr result_type max()
    {
        return std::numeric_limits<result_type>::max();
    }

    friend bool operator==(const RDRANDEngine<ResultType, NTrialMax> &,
        const RDRANDEngine<ResultType, NTrialMax> &)
    {
        return false;
    }

    friend bool operator!=(const RDRANDEngine<ResultType, NTrialMax> &,
        const RDRANDEngine<ResultType, NTrialMax> &)
    {
        return true;
    }

    template <typename CharT, typename CharTraits>
    friend std::basic_ostream<CharT, CharTraits> &operator<<(
        std::basic_ostream<CharT, CharTraits> &os,
        const RDRANDEngine<ResultType, NTrialMax> &)
    {
        return os;
    }

    template <typename CharT, typename CharTraits>
    friend std::basic_istream<CharT, CharTraits> &operator>>(
        std::basic_istream<CharT, CharTraits> &is,
        RDRANDEngine<ResultType, NTrialMax> &)
    {
        return is;
    }

    private:
    result_type generate(std::true_type)
    {
        result_type r;
        std::size_t ntrial = 0;
        while (true) {
            ++ntrial;
            bool success = rdrand<result_type>(
                &r, std::integral_constant<int,
                        std::numeric_limits<result_type>::digits>());
            if (success || ntrial > NTrialMax)
                break;
        }
        VSMC_RUNTIME_WARNING_RNG_RDRAND_ENGINE_NTRIAL(ntrial, NTrialMax);

        return r;
    }

    result_type generate(std::false_type)
    {
        result_type r;
        while (true) {
            bool success = rdrand<result_type>(
                &r, std::integral_constant<int,
                        std::numeric_limits<result_type>::digits>());
            if (success)
                break;
        }

        return r;
    }
}; // class RDRANDEngine

using RDRAND16 = RDRANDEngine<std::uint16_t>;

using RDRAND32 = RDRANDEngine<std::uint32_t>;

using RDRAND64 = RDRANDEngine<std::uint64_t>;

} // namespace vsmc

#endif //  VSMC_RNG_RDRAND_HPP