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// 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 "base/compiler_specific.h"
#include "base/component_export.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 COMPONENT_EXPORT(VARIATIONS) 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(const SHA1EntropyProvider&) = delete;
SHA1EntropyProvider& operator=(const SHA1EntropyProvider&) = delete;
~SHA1EntropyProvider() override;
// base::FieldTrial::EntropyProvider implementation:
double GetEntropyForTrial(base::StringPiece trial_name,
uint32_t randomization_seed) const override;
private:
const std::string entropy_source_;
};
// 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 COMPONENT_EXPORT(VARIATIONS) NormalizedMurmurHashEntropyProvider
: public base::FieldTrial::EntropyProvider {
public:
NormalizedMurmurHashEntropyProvider(uint16_t low_entropy_source,
size_t low_entropy_source_max);
NormalizedMurmurHashEntropyProvider(
const NormalizedMurmurHashEntropyProvider&) = delete;
NormalizedMurmurHashEntropyProvider& operator=(
const NormalizedMurmurHashEntropyProvider&) = delete;
~NormalizedMurmurHashEntropyProvider() override;
// base::FieldTrial::EntropyProvider:
double GetEntropyForTrial(base::StringPiece trial_name,
uint32_t randomization_seed) const override;
private:
const uint16_t low_entropy_source_;
const size_t low_entropy_source_max_;
};
} // namespace variations
#endif // COMPONENTS_VARIATIONS_ENTROPY_PROVIDER_H_
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