Create variations target that depends on base.

chrome/common/metrics/entropy_provider.h

-// 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 CHROME_COMMON_METRICS_ENTROPY_PROVIDER_H_
-#define CHROME_COMMON_METRICS_ENTROPY_PROVIDER_H_
-
-#include <functional>
-#include <string>
-#include <vector>
-
-#include "base/basictypes.h"
-#include "base/compiler_specific.h"
-#include "base/metrics/field_trial.h"
-#include "third_party/mt19937ar/mt19937ar.h"
-
-namespace metrics {
-
-// Internals of entropy_provider.cc exposed for testing.
-namespace internal {
-
-// A functor that generates random numbers based on a seed, using the Mersenne
-// Twister algorithm. Suitable for use with std::random_shuffle().
-struct SeededRandGenerator : std::unary_function<uint32, uint32> {
-  explicit SeededRandGenerator(uint32 seed);
-  ~SeededRandGenerator();
-
-  // Returns a random number in range [0, range).
-  uint32 operator()(uint32 range);
-
-  MersenneTwister mersenne_twister_;
-};
-
-// Fills |mapping| to create a bijection of values in the range of
-// [0, |mapping.size()|), permuted based on |randomization_seed|.
-void PermuteMappingUsingRandomizationSeed(uint32 randomization_seed,
-                                          std::vector<uint16>* mapping);
-
-}  // namespace internal
-
-// 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 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);
-  virtual ~SHA1EntropyProvider();
-
-  // base::FieldTrial::EntropyProvider implementation:
-  virtual double GetEntropyForTrial(const std::string& trial_name,
-                                    uint32 randomization_seed) const OVERRIDE;
-
- private:
-  std::string entropy_source_;
-
-  DISALLOW_COPY_AND_ASSIGN(SHA1EntropyProvider);
-};
-
-// PermutedEntropyProvider is an entropy provider suitable for low entropy
-// sources (below 16 bits). It uses the field trial name to generate a
-// permutation of a mapping array from an initial entropy value to a new value.
-// Note: This provider's performance is O(2^n), where n is the number of bits
-// in the entropy source.
-class PermutedEntropyProvider : public base::FieldTrial::EntropyProvider {
- public:
-  // Creates a PermutedEntropyProvider with the given |low_entropy_source|,
-  // which should have a value in the range of [0, low_entropy_source_max).
-  PermutedEntropyProvider(uint16 low_entropy_source,
-                          size_t low_entropy_source_max);
-  virtual ~PermutedEntropyProvider();
-
-  // base::FieldTrial::EntropyProvider implementation:
-  virtual double GetEntropyForTrial(const std::string& trial_name,
-                                    uint32 randomization_seed) const OVERRIDE;
-
- protected:
-  // Performs the permutation algorithm and returns the permuted value that
-  // corresponds to |low_entropy_source_|.
-  virtual uint16 GetPermutedValue(uint32 randomization_seed) const;
-
- private:
-  uint16 low_entropy_source_;
-  size_t low_entropy_source_max_;
-
-  DISALLOW_COPY_AND_ASSIGN(PermutedEntropyProvider);
-};
-
-}  // namespace metrics
-
-#endif  // CHROME_COMMON_METRICS_ENTROPY_PROVIDER_H_