1 /* 2 * Copyright (c) Facebook, Inc. and its affiliates. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef FOLLY_RANDOM_H_ 18 #error This file may only be included from folly/Random.h 19 #endif 20 21 namespace folly { 22 23 namespace detail { 24 25 // Return the state size needed by RNG, expressed as a number of uint32_t 26 // integers. Specialized for all templates specified in the C++11 standard. 27 // For some (mersenne_twister_engine), this is exported as a state_size static 28 // data member; for others, the standard shows formulas. 29 30 template <class RNG, typename = void> 31 struct StateSize { 32 // A sane default. 33 using type = std::integral_constant<size_t, 512>; 34 }; 35 36 template <class RNG> 37 struct StateSize<RNG, void_t<decltype(RNG::state_size)>> { 38 using type = std::integral_constant<size_t, RNG::state_size>; 39 }; 40 41 template <class UIntType, UIntType a, UIntType c, UIntType m> 42 struct StateSize<std::linear_congruential_engine<UIntType, a, c, m>> { 43 // From the standard [rand.eng.lcong], this is ceil(log2(m) / 32) + 3, 44 // which is the same as ceil(ceil(log2(m) / 32) + 3, and 45 // ceil(log2(m)) <= std::numeric_limits<UIntType>::digits 46 using type = std::integral_constant< 47 size_t, 48 (std::numeric_limits<UIntType>::digits + 31) / 32 + 3>; 49 }; 50 51 template <class UIntType, size_t w, size_t s, size_t r> 52 struct StateSize<std::subtract_with_carry_engine<UIntType, w, s, r>> { 53 // [rand.eng.sub]: r * ceil(w / 32) 54 using type = std::integral_constant<size_t, r*((w + 31) / 32)>; 55 }; 56 57 template <typename RNG> 58 using StateSizeT = _t<StateSize<RNG>>; 59 60 template <class RNG> 61 struct SeedData { 62 SeedData() { 63 Random::secureRandom(seedData.data(), seedData.size() * sizeof(uint32_t)); 64 } 65 66 static constexpr size_t stateSize = StateSizeT<RNG>::value; 67 std::array<uint32_t, stateSize> seedData; 68 }; 69 70 } // namespace detail 71 72 template <class RNG, class /* EnableIf */> 73 void Random::seed(RNG& rng) { 74 detail::SeedData<RNG> sd; 75 std::seed_seq s(std::begin(sd.seedData), std::end(sd.seedData)); 76 rng.seed(s); 77 } 78 79 template <class RNG, class /* EnableIf */> 80 auto Random::create() -> RNG { 81 detail::SeedData<RNG> sd; 82 std::seed_seq s(std::begin(sd.seedData), std::end(sd.seedData)); 83 return RNG(s); 84 } 85 86 } // namespace folly 87