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- /*
- * Copyright 2014-present Facebook, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- #ifndef FOLLY_RANDOM_H_
- #error This file may only be included from folly/Random.h
- #endif
- namespace folly {
- namespace detail {
- // Return the state size needed by RNG, expressed as a number of uint32_t
- // integers. Specialized for all templates specified in the C++11 standard.
- // For some (mersenne_twister_engine), this is exported as a state_size static
- // data member; for others, the standard shows formulas.
- template <class RNG, typename = void>
- struct StateSize {
- // A sane default.
- using type = std::integral_constant<size_t, 512>;
- };
- template <class RNG>
- struct StateSize<RNG, void_t<decltype(RNG::state_size)>> {
- using type = std::integral_constant<size_t, RNG::state_size>;
- };
- template <class UIntType, UIntType a, UIntType c, UIntType m>
- struct StateSize<std::linear_congruential_engine<UIntType, a, c, m>> {
- // From the standard [rand.eng.lcong], this is ceil(log2(m) / 32) + 3,
- // which is the same as ceil(ceil(log2(m) / 32) + 3, and
- // ceil(log2(m)) <= std::numeric_limits<UIntType>::digits
- using type = std::integral_constant<
- size_t,
- (std::numeric_limits<UIntType>::digits + 31) / 32 + 3>;
- };
- template <class UIntType, size_t w, size_t s, size_t r>
- struct StateSize<std::subtract_with_carry_engine<UIntType, w, s, r>> {
- // [rand.eng.sub]: r * ceil(w / 32)
- using type = std::integral_constant<size_t, r*((w + 31) / 32)>;
- };
- template <typename RNG>
- using StateSizeT = _t<StateSize<RNG>>;
- template <class RNG>
- struct SeedData {
- SeedData() {
- Random::secureRandom(seedData.data(), seedData.size() * sizeof(uint32_t));
- }
- static constexpr size_t stateSize = StateSizeT<RNG>::value;
- std::array<uint32_t, stateSize> seedData;
- };
- } // namespace detail
- template <class RNG, class /* EnableIf */>
- void Random::seed(RNG& rng) {
- detail::SeedData<RNG> sd;
- std::seed_seq s(std::begin(sd.seedData), std::end(sd.seedData));
- rng.seed(s);
- }
- template <class RNG, class /* EnableIf */>
- auto Random::create() -> RNG {
- detail::SeedData<RNG> sd;
- std::seed_seq s(std::begin(sd.seedData), std::end(sd.seedData));
- return RNG(s);
- }
- } // namespace folly
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