| // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef COMPONENTS_VARIATIONS_ENTROPY_PROVIDER_H_ |
| #define COMPONENTS_VARIATIONS_ENTROPY_PROVIDER_H_ |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #include <functional> |
| #include <random> |
| #include <string> |
| #include <vector> |
| |
| #include "base/compiler_specific.h" |
| #include "base/macros.h" |
| #include "base/metrics/field_trial.h" |
| |
| namespace variations { |
| |
| // SHA1EntropyProvider is an entropy provider suitable for high entropy sources. |
| // It works by taking the first 64 bits of the SHA1 hash of the entropy source |
| // concatenated with the trial name, or randomization seed and using that for |
| // the final entropy value. |
| class SHA1EntropyProvider : public base::FieldTrial::EntropyProvider { |
| public: |
| // Creates a SHA1EntropyProvider with the given |entropy_source|, which |
| // should contain a large amount of entropy - for example, a textual |
| // representation of a persistent randomly-generated 128-bit value. |
| explicit SHA1EntropyProvider(const std::string& entropy_source); |
| ~SHA1EntropyProvider() override; |
| |
| // base::FieldTrial::EntropyProvider implementation: |
| double GetEntropyForTrial(const std::string& trial_name, |
| uint32_t randomization_seed) const override; |
| |
| private: |
| const std::string entropy_source_; |
| |
| DISALLOW_COPY_AND_ASSIGN(SHA1EntropyProvider); |
| }; |
| |
| // NormalizedMurmurHashEntropyProvider is an entropy provider suitable for low |
| // entropy sources (below 16 bits). It uses MurmurHash3_32 to hash the study |
| // name along with all possible low entropy sources. It finds the index where |
| // the actual low entropy source's hash would fall in the sorted list of all |
| // those hashes, and uses that as the final value. For more info, see: |
| // https://docs.google.com/document/d/1cPF5PruriWNP2Z5gSkq4MBTm0wSZqLyIJkUO9ekibeo |
| class NormalizedMurmurHashEntropyProvider |
| : public base::FieldTrial::EntropyProvider { |
| public: |
| NormalizedMurmurHashEntropyProvider(uint16_t low_entropy_source, |
| size_t low_entropy_source_max); |
| ~NormalizedMurmurHashEntropyProvider() override; |
| |
| // base::FieldTrial::EntropyProvider: |
| double GetEntropyForTrial(const std::string& trial_name, |
| uint32_t randomization_seed) const override; |
| |
| private: |
| const uint16_t low_entropy_source_; |
| const size_t low_entropy_source_max_; |
| |
| DISALLOW_COPY_AND_ASSIGN(NormalizedMurmurHashEntropyProvider); |
| }; |
| |
| } // namespace variations |
| |
| #endif // COMPONENTS_VARIATIONS_ENTROPY_PROVIDER_H_ |