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136 lines
4.7 KiB
C++
136 lines
4.7 KiB
C++
/*
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* Copyright 2016 Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef FOLLY_RANDOM_H_
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#error This file may only be included from folly/Random.h
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#endif
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#include <array>
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namespace folly {
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namespace detail {
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// Return the state size needed by RNG, expressed as a number of uint32_t
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// integers. Specialized for all templates specified in the C++11 standard.
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// For some (mersenne_twister_engine), this is exported as a state_size static
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// data member; for others, the standard shows formulas.
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template <class RNG> struct StateSize {
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// A sane default.
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static constexpr size_t value = 512;
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};
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template <class RNG>
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constexpr size_t StateSize<RNG>::value;
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template <class UIntType, UIntType a, UIntType c, UIntType m>
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struct StateSize<std::linear_congruential_engine<UIntType, a, c, m>> {
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// From the standard [rand.eng.lcong], this is ceil(log2(m) / 32) + 3,
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// which is the same as ceil(ceil(log2(m) / 32) + 3, and
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// ceil(log2(m)) <= std::numeric_limits<UIntType>::digits
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static constexpr size_t value =
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(std::numeric_limits<UIntType>::digits + 31) / 32 + 3;
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};
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template <class UIntType, UIntType a, UIntType c, UIntType m>
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constexpr size_t
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StateSize<std::linear_congruential_engine<UIntType, a, c, m>>::value;
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template <class UIntType, size_t w, size_t n, size_t m, size_t r,
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UIntType a, size_t u, UIntType d, size_t s,
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UIntType b, size_t t,
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UIntType c, size_t l, UIntType f>
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struct StateSize<std::mersenne_twister_engine<UIntType, w, n, m, r,
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a, u, d, s, b, t, c, l, f>> {
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static constexpr size_t value =
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std::mersenne_twister_engine<UIntType, w, n, m, r,
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a, u, d, s, b, t, c, l, f>::state_size;
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};
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template <class UIntType, size_t w, size_t n, size_t m, size_t r,
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UIntType a, size_t u, UIntType d, size_t s,
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UIntType b, size_t t,
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UIntType c, size_t l, UIntType f>
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constexpr size_t
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StateSize<std::mersenne_twister_engine<UIntType, w, n, m, r,
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a, u, d, s, b, t, c, l, f>>::value;
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#if FOLLY_HAVE_EXTRANDOM_SFMT19937
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template <class UIntType, size_t m, size_t pos1, size_t sl1, size_t sl2,
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size_t sr1, size_t sr2, uint32_t msk1, uint32_t msk2, uint32_t msk3,
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uint32_t msk4, uint32_t parity1, uint32_t parity2, uint32_t parity3,
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uint32_t parity4>
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struct StateSize<__gnu_cxx::simd_fast_mersenne_twister_engine<
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UIntType, m, pos1, sl1, sl2, sr1, sr2, msk1, msk2, msk3, msk4,
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parity1, parity2, parity3, parity4>> {
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static constexpr size_t value =
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__gnu_cxx::simd_fast_mersenne_twister_engine<
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UIntType, m, pos1, sl1, sl2, sr1, sr2,
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msk1, msk2, msk3, msk4,
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parity1, parity2, parity3, parity4>::state_size;
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};
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template <class UIntType, size_t m, size_t pos1, size_t sl1, size_t sl2,
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size_t sr1, size_t sr2, uint32_t msk1, uint32_t msk2, uint32_t msk3,
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uint32_t msk4, uint32_t parity1, uint32_t parity2, uint32_t parity3,
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uint32_t parity4>
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constexpr size_t
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StateSize<__gnu_cxx::simd_fast_mersenne_twister_engine<
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UIntType, m, pos1, sl1, sl2, sr1, sr2, msk1, msk2, msk3, msk4,
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parity1, parity2, parity3, parity4>>::value;
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#endif
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template <class UIntType, size_t w, size_t s, size_t r>
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struct StateSize<std::subtract_with_carry_engine<UIntType, w, s, r>> {
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// [rand.eng.sub]: r * ceil(w / 32)
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static constexpr size_t value = r * ((w + 31) / 32);
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};
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template <class UIntType, size_t w, size_t s, size_t r>
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constexpr size_t
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StateSize<std::subtract_with_carry_engine<UIntType, w, s, r>>::value;
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template <class RNG>
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struct SeedData {
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SeedData() {
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Random::secureRandom(seedData.data(), seedData.size() * sizeof(uint32_t));
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}
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static constexpr size_t stateSize = StateSize<RNG>::value;
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std::array<uint32_t, stateSize> seedData;
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};
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} // namespace detail
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template <class RNG, class /* EnableIf */>
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void Random::seed(RNG& rng) {
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detail::SeedData<RNG> sd;
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std::seed_seq s(std::begin(sd.seedData), std::end(sd.seedData));
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rng.seed(s);
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}
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template <class RNG, class /* EnableIf */>
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auto Random::create() -> RNG {
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detail::SeedData<RNG> sd;
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std::seed_seq s(std::begin(sd.seedData), std::end(sd.seedData));
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return RNG(s);
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}
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} // namespaces
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