1 | /* |
2 | * Copyright 2014-present Facebook, Inc. |
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 | |