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Diffstat (limited to 'third_party/abseil_cpp/absl/random/internal/salted_seed_seq.h')
-rw-r--r-- | third_party/abseil_cpp/absl/random/internal/salted_seed_seq.h | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/random/internal/salted_seed_seq.h b/third_party/abseil_cpp/absl/random/internal/salted_seed_seq.h new file mode 100644 index 000000000000..5953a090f80c --- /dev/null +++ b/third_party/abseil_cpp/absl/random/internal/salted_seed_seq.h @@ -0,0 +1,167 @@ +// 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. + +#ifndef ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_ +#define ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_ + +#include <cstdint> +#include <cstdlib> +#include <initializer_list> +#include <iterator> +#include <memory> +#include <type_traits> +#include <utility> + +#include "absl/container/inlined_vector.h" +#include "absl/meta/type_traits.h" +#include "absl/random/internal/seed_material.h" +#include "absl/types/optional.h" +#include "absl/types/span.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace random_internal { + +// This class conforms to the C++ Standard "Seed Sequence" concept +// [rand.req.seedseq]. +// +// A `SaltedSeedSeq` is meant to wrap an existing seed sequence and modify +// generated sequence by mixing with extra entropy. This entropy may be +// build-dependent or process-dependent. The implementation may change to be +// have either or both kinds of entropy. If salt is not available sequence is +// not modified. +template <typename SSeq> +class SaltedSeedSeq { + public: + using inner_sequence_type = SSeq; + using result_type = typename SSeq::result_type; + + SaltedSeedSeq() : seq_(absl::make_unique<SSeq>()) {} + + template <typename Iterator> + SaltedSeedSeq(Iterator begin, Iterator end) + : seq_(absl::make_unique<SSeq>(begin, end)) {} + + template <typename T> + SaltedSeedSeq(std::initializer_list<T> il) + : SaltedSeedSeq(il.begin(), il.end()) {} + + SaltedSeedSeq(const SaltedSeedSeq&) = delete; + SaltedSeedSeq& operator=(const SaltedSeedSeq&) = delete; + + SaltedSeedSeq(SaltedSeedSeq&&) = default; + SaltedSeedSeq& operator=(SaltedSeedSeq&&) = default; + + template <typename RandomAccessIterator> + void generate(RandomAccessIterator begin, RandomAccessIterator end) { + // The common case is that generate is called with ContiguousIterators + // to uint arrays. Such contiguous memory regions may be optimized, + // which we detect here. + using tag = absl::conditional_t< + (std::is_pointer<RandomAccessIterator>::value && + std::is_same<absl::decay_t<decltype(*begin)>, uint32_t>::value), + ContiguousAndUint32Tag, DefaultTag>; + if (begin != end) { + generate_impl(begin, end, tag{}); + } + } + + template <typename OutIterator> + void param(OutIterator out) const { + seq_->param(out); + } + + size_t size() const { return seq_->size(); } + + private: + struct ContiguousAndUint32Tag {}; + struct DefaultTag {}; + + // Generate which requires the iterators are contiguous pointers to uint32_t. + void generate_impl(uint32_t* begin, uint32_t* end, ContiguousAndUint32Tag) { + generate_contiguous(absl::MakeSpan(begin, end)); + } + + // The uncommon case for generate is that it is called with iterators over + // some other buffer type which is assignable from a 32-bit value. In this + // case we allocate a temporary 32-bit buffer and then copy-assign back + // to the initial inputs. + template <typename RandomAccessIterator> + void generate_impl(RandomAccessIterator begin, RandomAccessIterator end, + DefaultTag) { + return generate_and_copy(std::distance(begin, end), begin); + } + + // Fills the initial seed buffer the underlying SSeq::generate() call, + // mixing in the salt material. + void generate_contiguous(absl::Span<uint32_t> buffer) { + seq_->generate(buffer.begin(), buffer.end()); + const uint32_t salt = absl::random_internal::GetSaltMaterial().value_or(0); + MixIntoSeedMaterial(absl::MakeConstSpan(&salt, 1), buffer); + } + + // Allocates a seed buffer of `n` elements, generates the seed, then + // copies the result into the `out` iterator. + template <typename Iterator> + void generate_and_copy(size_t n, Iterator out) { + // Allocate a temporary buffer, generate, and then copy. + absl::InlinedVector<uint32_t, 8> data(n, 0); + generate_contiguous(absl::MakeSpan(data.data(), data.size())); + std::copy(data.begin(), data.end(), out); + } + + // Because [rand.req.seedseq] is not required to be copy-constructible, + // copy-assignable nor movable, we wrap it with unique pointer to be able + // to move SaltedSeedSeq. + std::unique_ptr<SSeq> seq_; +}; + +// is_salted_seed_seq indicates whether the type is a SaltedSeedSeq. +template <typename T, typename = void> +struct is_salted_seed_seq : public std::false_type {}; + +template <typename T> +struct is_salted_seed_seq< + T, typename std::enable_if<std::is_same< + T, SaltedSeedSeq<typename T::inner_sequence_type>>::value>::type> + : public std::true_type {}; + +// MakeSaltedSeedSeq returns a salted variant of the seed sequence. +// When provided with an existing SaltedSeedSeq, returns the input parameter, +// otherwise constructs a new SaltedSeedSeq which embodies the original +// non-salted seed parameters. +template < + typename SSeq, // + typename EnableIf = absl::enable_if_t<is_salted_seed_seq<SSeq>::value>> +SSeq MakeSaltedSeedSeq(SSeq&& seq) { + return SSeq(std::forward<SSeq>(seq)); +} + +template < + typename SSeq, // + typename EnableIf = absl::enable_if_t<!is_salted_seed_seq<SSeq>::value>> +SaltedSeedSeq<typename std::decay<SSeq>::type> MakeSaltedSeedSeq(SSeq&& seq) { + using sseq_type = typename std::decay<SSeq>::type; + using result_type = typename sseq_type::result_type; + + absl::InlinedVector<result_type, 8> data; + seq.param(std::back_inserter(data)); + return SaltedSeedSeq<sseq_type>(data.begin(), data.end()); +} + +} // namespace random_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_ |