| // Copyright 2017 The Abseil Authors. |
| // |
| // 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 |
| // |
| // https://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. |
| // |
| // ----------------------------------------------------------------------------- |
| // File: seed_sequences.h |
| // ----------------------------------------------------------------------------- |
| // |
| // This header contains utilities for creating and working with seed sequences |
| // conforming to [rand.req.seedseq]. In general, direct construction of seed |
| // sequences is discouraged, but use-cases for construction of identical bit |
| // generators (using the same seed sequence) may be helpful (e.g. replaying a |
| // simulation whose state is derived from variates of a bit generator). |
| |
| #ifndef ABSL_RANDOM_SEED_SEQUENCES_H_ |
| #define ABSL_RANDOM_SEED_SEQUENCES_H_ |
| |
| #include <iterator> |
| #include <random> |
| |
| #include "absl/base/config.h" |
| #include "absl/base/nullability.h" |
| #include "absl/random/internal/salted_seed_seq.h" |
| #include "absl/random/internal/seed_material.h" |
| #include "absl/random/seed_gen_exception.h" |
| #include "absl/strings/string_view.h" |
| #include "absl/types/span.h" |
| |
| namespace absl { |
| ABSL_NAMESPACE_BEGIN |
| |
| // ----------------------------------------------------------------------------- |
| // absl::SeedSeq |
| // ----------------------------------------------------------------------------- |
| // |
| // `absl::SeedSeq` constructs a seed sequence according to [rand.req.seedseq] |
| // for use within bit generators. `absl::SeedSeq`, unlike `std::seed_seq` |
| // additionally salts the generated seeds with extra implementation-defined |
| // entropy. For that reason, you can use `absl::SeedSeq` in combination with |
| // standard library bit generators (e.g. `std::mt19937`) to introduce |
| // non-determinism in your seeds. |
| // |
| // Example: |
| // |
| // absl::SeedSeq my_seed_seq({a, b, c}); |
| // std::mt19937 my_bitgen(my_seed_seq); |
| // |
| using SeedSeq = random_internal::SaltedSeedSeq<std::seed_seq>; |
| |
| // ----------------------------------------------------------------------------- |
| // absl::CreateSeedSeqFrom(bitgen*) |
| // ----------------------------------------------------------------------------- |
| // |
| // Constructs a seed sequence conforming to [rand.req.seedseq] using variates |
| // produced by a provided bit generator. |
| // |
| // You should generally avoid direct construction of seed sequences, but |
| // use-cases for reuse of a seed sequence to construct identical bit generators |
| // may be helpful (eg. replaying a simulation whose state is derived from bit |
| // generator values). |
| // |
| // If bitgen == nullptr, then behavior is undefined. |
| // |
| // Example: |
| // |
| // absl::BitGen my_bitgen; |
| // auto seed_seq = absl::CreateSeedSeqFrom(&my_bitgen); |
| // absl::BitGen new_engine(seed_seq); // derived from my_bitgen, but not |
| // // correlated. |
| // |
| template <typename URBG> |
| SeedSeq CreateSeedSeqFrom(URBG* urbg) { |
| SeedSeq::result_type |
| seed_material[random_internal::kEntropyBlocksNeeded]; |
| |
| if (!random_internal::ReadSeedMaterialFromURBG( |
| urbg, absl::MakeSpan(seed_material))) { |
| random_internal::ThrowSeedGenException(); |
| } |
| return SeedSeq(std::begin(seed_material), std::end(seed_material)); |
| } |
| |
| // ----------------------------------------------------------------------------- |
| // absl::MakeSeedSeq() |
| // ----------------------------------------------------------------------------- |
| // |
| // Constructs an `absl::SeedSeq` salting the generated values using |
| // implementation-defined entropy. The returned sequence can be used to create |
| // equivalent bit generators correlated using this sequence. |
| // |
| // Example: |
| // |
| // auto my_seed_seq = absl::MakeSeedSeq(); |
| // std::mt19937 rng1(my_seed_seq); |
| // std::mt19937 rng2(my_seed_seq); |
| // EXPECT_EQ(rng1(), rng2()); |
| // |
| SeedSeq MakeSeedSeq(); |
| |
| ABSL_NAMESPACE_END |
| } // namespace absl |
| |
| #endif // ABSL_RANDOM_SEED_SEQUENCES_H_ |