Abseil Common Libraries (C++) (grcp 依赖)
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102 lines
3.5 KiB
102 lines
3.5 KiB
// Copyright 2017 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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#ifndef ABSL_RANDOM_INTERNAL_SEED_MATERIAL_H_ |
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#define ABSL_RANDOM_INTERNAL_SEED_MATERIAL_H_ |
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#include <cassert> |
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#include <cstdint> |
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#include <cstdlib> |
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#include <string> |
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#include <vector> |
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#include "absl/base/attributes.h" |
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#include "absl/random/internal/fast_uniform_bits.h" |
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#include "absl/types/optional.h" |
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#include "absl/types/span.h" |
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namespace absl { |
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namespace random_internal { |
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// Returns the number of 32-bit blocks needed to contain the given number of |
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// bits. |
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constexpr size_t SeedBitsToBlocks(size_t seed_size) { |
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return (seed_size + 31) / 32; |
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} |
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// Amount of entropy (measured in bits) used to instantiate a Seed Sequence, |
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// with which to create a URBG. |
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constexpr size_t kEntropyBitsNeeded = 256; |
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// Amount of entropy (measured in 32-bit blocks) used to instantiate a Seed |
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// Sequence, with which to create a URBG. |
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constexpr size_t kEntropyBlocksNeeded = |
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random_internal::SeedBitsToBlocks(kEntropyBitsNeeded); |
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static_assert(kEntropyBlocksNeeded > 0, |
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"Entropy used to seed URBGs must be nonzero."); |
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// Attempts to fill a span of uint32_t-values using an OS-provided source of |
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// true entropy (eg. /dev/urandom) into an array of uint32_t blocks of data. The |
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// resulting array may be used to initialize an instance of a class conforming |
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// to the C++ Standard "Seed Sequence" concept [rand.req.seedseq]. |
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// |
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// If values.data() == nullptr, the behavior is undefined. |
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ABSL_MUST_USE_RESULT |
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bool ReadSeedMaterialFromOSEntropy(absl::Span<uint32_t> values); |
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// Attempts to fill a span of uint32_t-values using variates generated by an |
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// existing instance of a class conforming to the C++ Standard "Uniform Random |
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// Bit Generator" concept [rand.req.urng]. The resulting data may be used to |
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// initialize an instance of a class conforming to the C++ Standard |
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// "Seed Sequence" concept [rand.req.seedseq]. |
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// |
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// If urbg == nullptr or values.data() == nullptr, the behavior is undefined. |
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template <typename URBG> |
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ABSL_MUST_USE_RESULT bool ReadSeedMaterialFromURBG( |
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URBG* urbg, absl::Span<uint32_t> values) { |
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random_internal::FastUniformBits<uint32_t> distr; |
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assert(urbg != nullptr && values.data() != nullptr); |
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if (urbg == nullptr || values.data() == nullptr) { |
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return false; |
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} |
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for (uint32_t& seed_value : values) { |
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seed_value = distr(*urbg); |
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} |
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return true; |
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} |
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// Mixes given sequence of values with into given sequence of seed material. |
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// Time complexity of this function is O(sequence.size() * |
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// seed_material.size()). |
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// |
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// Algorithm is based on code available at |
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// https://gist.github.com/imneme/540829265469e673d045 |
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// by Melissa O'Neill. |
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void MixIntoSeedMaterial(absl::Span<const uint32_t> sequence, |
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absl::Span<uint32_t> seed_material); |
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// Returns salt value. |
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// |
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// Salt is obtained only once and stored in static variable. |
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// |
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// May return empty value if optaining the salt was not possible. |
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absl::optional<uint32_t> GetSaltMaterial(); |
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} // namespace random_internal |
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} // namespace absl |
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#endif // ABSL_RANDOM_INTERNAL_SEED_MATERIAL_H_
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