87 lines
2.7 KiB
C++
87 lines
2.7 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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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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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, typename = void>
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struct StateSize {
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// A sane default.
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using type = std::integral_constant<size_t, 512>;
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};
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template <class RNG>
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struct StateSize<RNG, void_t<decltype(RNG::state_size)>> {
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using type = std::integral_constant<size_t, RNG::state_size>;
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};
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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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using type = std::integral_constant<
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size_t,
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(std::numeric_limits<UIntType>::digits + 31) / 32 + 3>;
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};
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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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using type = std::integral_constant<size_t, r*((w + 31) / 32)>;
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};
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template <typename RNG>
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using StateSizeT = _t<StateSize<RNG>>;
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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 = StateSizeT<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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} // namespace folly
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