base/rand_util.h - chromium/src - Git at Google

 // Copyright 2012 The Chromium Authors
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #ifndef BASE_RAND_UTIL_H_
 #define BASE_RAND_UTIL_H_

 #include <stddef.h>
 #include <stdint.h>

 #include <algorithm>
 #include <string>

 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "build/build_config.h"

 #if !BUILDFLAG(IS_NACL)
 #include "third_party/boringssl/src/include/openssl/rand.h"
 #endif

 namespace memory_simulator {
 class MemoryHolder;
 }

 namespace base {

 class TimeDelta;

 namespace internal {

 #if BUILDFLAG(IS_ANDROID)
 // Sets the implementation of RandBytes according to the corresponding
 // base::Feature. Thread safe: allows to switch while RandBytes() is in use.
 void ConfigureRandBytesFieldTrial();
 #endif

 #if !BUILDFLAG(IS_NACL)
 void ConfigureBoringSSLBackedRandBytesFieldTrial();
 #endif

 // Returns a random double in range [0, 1). For use in allocator shim to avoid
 // infinite recursion. Thread-safe.
 BASE_EXPORT double RandDoubleAvoidAllocation();

 }  // namespace internal

 // Returns a random number in range [0, UINT64_MAX]. Thread-safe.
 BASE_EXPORT uint64_t RandUint64();

 // Returns a random number between min and max (inclusive). Thread-safe.
 //
 // TODO(crbug.com/1488681): Change from fully-closed to half-closed (i.e.
 // exclude `max`) to parallel other APIs here.
 BASE_EXPORT int RandInt(int min, int max);

 // Returns a random number in range [0, range).  Thread-safe.
 BASE_EXPORT uint64_t RandGenerator(uint64_t range);

 // Returns a random double in range [0, 1). Thread-safe.
 BASE_EXPORT double RandDouble();

 // Returns a random float in range [0, 1). Thread-safe.
 BASE_EXPORT float RandFloat();

 // Returns a random duration in [`start`, `limit`). Thread-safe.
 //
 // REQUIRES: `start` < `limit`
 BASE_EXPORT TimeDelta RandTimeDelta(TimeDelta start, TimeDelta limit);

 // Returns a random duration in [`TimeDelta()`, `limit`). Thread-safe.
 //
 // REQUIRES: `limit.is_positive()`
 BASE_EXPORT TimeDelta RandTimeDeltaUpTo(TimeDelta limit);

 // Given input |bits|, convert with maximum precision to a double in
 // the range [0, 1). Thread-safe.
 BASE_EXPORT double BitsToOpenEndedUnitInterval(uint64_t bits);

 // Given input `bits`, convert with maximum precision to a float in the range
 // [0, 1). Thread-safe.
 BASE_EXPORT float BitsToOpenEndedUnitIntervalF(uint64_t bits);

 // Fills |output_length| bytes of |output| with random data. Thread-safe.
 //
 // Although implementations are required to use a cryptographically secure
 // random number source, code outside of base/ that relies on this should use
 // crypto::RandBytes instead to ensure the requirement is easily discoverable.
 BASE_EXPORT void RandBytes(void* output, size_t output_length);

 // Fills a string of length |length| with random data and returns it.
 // |length| should be nonzero. Thread-safe.
 //
 // Note that this is a variation of |RandBytes| with a different return type.
 // The returned string is likely not ASCII/UTF-8. Use with care.
 //
 // Although implementations are required to use a cryptographically secure
 // random number source, code outside of base/ that relies on this should use
 // crypto::RandBytes instead to ensure the requirement is easily discoverable.
 BASE_EXPORT std::string RandBytesAsString(size_t length);

 // An STL UniformRandomBitGenerator backed by RandUint64.
 class RandomBitGenerator {
  public:
   using result_type = uint64_t;
   static constexpr result_type min() { return 0; }
   static constexpr result_type max() { return UINT64_MAX; }
   result_type operator()() const { return RandUint64(); }

   RandomBitGenerator() = default;
   ~RandomBitGenerator() = default;
 };

 #if !BUILDFLAG(IS_NACL)
 class NonAllocatingRandomBitGenerator {
  public:
   using result_type = uint64_t;
   static constexpr result_type min() { return 0; }
   static constexpr result_type max() { return UINT64_MAX; }
   result_type operator()() const {
     uint64_t result;
     RAND_get_system_entropy_for_custom_prng(reinterpret_cast<uint8_t*>(&result),
                                             sizeof(result));
     return result;
   }

   NonAllocatingRandomBitGenerator() = default;
   ~NonAllocatingRandomBitGenerator() = default;
 };
 #endif

 // Shuffles [first, last) randomly. Thread-safe.
 template <typename Itr>
 void RandomShuffle(Itr first, Itr last) {
   std::shuffle(first, last, RandomBitGenerator());
 }

 #if BUILDFLAG(IS_POSIX)
 BASE_EXPORT int GetUrandomFD();
 #endif

 class MetricsSubSampler;

 // Fast, insecure pseudo-random number generator.
 //
 // WARNING: This is not the generator you are looking for. This has significant
 // caveats:
 //   - It is non-cryptographic, so easy to miuse
 //   - It is neither fork() nor clone()-safe.
 //   - Synchronization is up to the client.
 //
 // Always prefer base::Rand*() above, unless you have a use case where its
 // overhead is too high, or system calls are disallowed.
 //
 // Performance: As of 2021, rough overhead on Linux on a desktop machine of
 // base::RandUint64() is ~800ns per call (it performs a system call). On Windows
 // it is lower. On the same machine, this generator's cost is ~2ns per call,
 // regardless of platform.
 //
 // This is different from |Rand*()| above as it is guaranteed to never make a
 // system call to generate a new number, except to seed it.  This should *never*
 // be used for cryptographic applications, and is not thread-safe.
 //
 // It is seeded using base::RandUint64() in the constructor, meaning that it
 // doesn't need to be seeded. It can be re-seeded though, with
 // ReseedForTesting(). Its period is long enough that it should not need to be
 // re-seeded during use.
 //
 // Uses the XorShift128+ generator under the hood.
 class BASE_EXPORT InsecureRandomGenerator {
  public:
   // Never use outside testing, not enough entropy.
   void ReseedForTesting(uint64_t seed);

   uint32_t RandUint32();
   uint64_t RandUint64();
   // In [0, 1).
   double RandDouble();

  private:
   InsecureRandomGenerator();
   // State.
   uint64_t a_ = 0, b_ = 0;

   // Before adding a new friend class, make sure that the overhead of
   // base::Rand*() is too high, using something more representative than a
   // microbenchmark.

   // Uses the generator to fill memory pages with random content to make them
   // hard to compress, in a simulation tool not bundled with Chrome. CPU
   // overhead must be minimized to correctly measure memory effects.
   friend class memory_simulator::MemoryHolder;
   // Uses the generator to sub-sample metrics.
   friend class MetricsSubSampler;

   FRIEND_TEST_ALL_PREFIXES(RandUtilTest,
                            InsecureRandomGeneratorProducesBothValuesOfAllBits);
   FRIEND_TEST_ALL_PREFIXES(RandUtilTest, InsecureRandomGeneratorChiSquared);
   FRIEND_TEST_ALL_PREFIXES(RandUtilTest, InsecureRandomGeneratorRandDouble);
   FRIEND_TEST_ALL_PREFIXES(RandUtilPerfTest, InsecureRandomRandUint64);
 };

 class BASE_EXPORT MetricsSubSampler {
  public:
   MetricsSubSampler();
   bool ShouldSample(double probability);

   // Disables subsampling in a scope. Useful for testing.
   class BASE_EXPORT ScopedDisableForTesting {
    public:
     ScopedDisableForTesting();
     ~ScopedDisableForTesting();
   };

  private:
   InsecureRandomGenerator generator_;
 };

 }  // namespace base

 #endif  // BASE_RAND_UTIL_H_
	// Copyright 2012 The Chromium Authors
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#ifndef BASE_RAND_UTIL_H_
	#define BASE_RAND_UTIL_H_

	#include <stddef.h>
	#include <stdint.h>

	#include <algorithm>
	#include <string>

	#include "base/base_export.h"
	#include "base/compiler_specific.h"
	#include "base/gtest_prod_util.h"
	#include "build/build_config.h"

	#if !BUILDFLAG(IS_NACL)
	#include "third_party/boringssl/src/include/openssl/rand.h"
	#endif

	namespace memory_simulator {
	class MemoryHolder;
	}

	namespace base {

	class TimeDelta;

	namespace internal {

	#if BUILDFLAG(IS_ANDROID)
	// Sets the implementation of RandBytes according to the corresponding
	// base::Feature. Thread safe: allows to switch while RandBytes() is in use.
	void ConfigureRandBytesFieldTrial();
	#endif

	#if !BUILDFLAG(IS_NACL)
	void ConfigureBoringSSLBackedRandBytesFieldTrial();
	#endif

	// Returns a random double in range [0, 1). For use in allocator shim to avoid
	// infinite recursion. Thread-safe.
	BASE_EXPORT double RandDoubleAvoidAllocation();

	} // namespace internal

	// Returns a random number in range [0, UINT64_MAX]. Thread-safe.
	BASE_EXPORT uint64_t RandUint64();

	// Returns a random number between min and max (inclusive). Thread-safe.
	//
	// TODO(crbug.com/1488681): Change from fully-closed to half-closed (i.e.
	// exclude `max`) to parallel other APIs here.
	BASE_EXPORT int RandInt(int min, int max);

	// Returns a random number in range [0, range). Thread-safe.
	BASE_EXPORT uint64_t RandGenerator(uint64_t range);

	// Returns a random double in range [0, 1). Thread-safe.
	BASE_EXPORT double RandDouble();

	// Returns a random float in range [0, 1). Thread-safe.
	BASE_EXPORT float RandFloat();

	// Returns a random duration in [`start`, `limit`). Thread-safe.
	//
	// REQUIRES: `start` < `limit`
	BASE_EXPORT TimeDelta RandTimeDelta(TimeDelta start, TimeDelta limit);

	// Returns a random duration in [`TimeDelta()`, `limit`). Thread-safe.
	//
	// REQUIRES: `limit.is_positive()`
	BASE_EXPORT TimeDelta RandTimeDeltaUpTo(TimeDelta limit);

	// Given input \|bits\|, convert with maximum precision to a double in
	// the range [0, 1). Thread-safe.
	BASE_EXPORT double BitsToOpenEndedUnitInterval(uint64_t bits);

	// Given input `bits`, convert with maximum precision to a float in the range
	// [0, 1). Thread-safe.
	BASE_EXPORT float BitsToOpenEndedUnitIntervalF(uint64_t bits);

	// Fills \|output_length\| bytes of \|output\| with random data. Thread-safe.
	//
	// Although implementations are required to use a cryptographically secure
	// random number source, code outside of base/ that relies on this should use
	// crypto::RandBytes instead to ensure the requirement is easily discoverable.
	BASE_EXPORT void RandBytes(void* output, size_t output_length);

	// Fills a string of length \|length\| with random data and returns it.
	// \|length\| should be nonzero. Thread-safe.
	//
	// Note that this is a variation of \|RandBytes\| with a different return type.
	// The returned string is likely not ASCII/UTF-8. Use with care.
	//
	// Although implementations are required to use a cryptographically secure
	// random number source, code outside of base/ that relies on this should use
	// crypto::RandBytes instead to ensure the requirement is easily discoverable.
	BASE_EXPORT std::string RandBytesAsString(size_t length);

	// An STL UniformRandomBitGenerator backed by RandUint64.
	class RandomBitGenerator {
	public:
	using result_type = uint64_t;
	static constexpr result_type min() { return 0; }
	static constexpr result_type max() { return UINT64_MAX; }
	result_type operator()() const { return RandUint64(); }

	RandomBitGenerator() = default;
	~RandomBitGenerator() = default;
	};

	#if !BUILDFLAG(IS_NACL)
	class NonAllocatingRandomBitGenerator {
	public:
	using result_type = uint64_t;
	static constexpr result_type min() { return 0; }
	static constexpr result_type max() { return UINT64_MAX; }
	result_type operator()() const {
	uint64_t result;
	RAND_get_system_entropy_for_custom_prng(reinterpret_cast<uint8_t*>(&result),
	sizeof(result));
	return result;
	}

	NonAllocatingRandomBitGenerator() = default;
	~NonAllocatingRandomBitGenerator() = default;
	};
	#endif

	// Shuffles [first, last) randomly. Thread-safe.
	template <typename Itr>
	void RandomShuffle(Itr first, Itr last) {
	std::shuffle(first, last, RandomBitGenerator());
	}

	#if BUILDFLAG(IS_POSIX)
	BASE_EXPORT int GetUrandomFD();
	#endif

	class MetricsSubSampler;

	// Fast, insecure pseudo-random number generator.
	//
	// WARNING: This is not the generator you are looking for. This has significant
	// caveats:
	// - It is non-cryptographic, so easy to miuse
	// - It is neither fork() nor clone()-safe.
	// - Synchronization is up to the client.
	//
	// Always prefer base::Rand*() above, unless you have a use case where its
	// overhead is too high, or system calls are disallowed.
	//
	// Performance: As of 2021, rough overhead on Linux on a desktop machine of
	// base::RandUint64() is ~800ns per call (it performs a system call). On Windows
	// it is lower. On the same machine, this generator's cost is ~2ns per call,
	// regardless of platform.
	//
	// This is different from \|Rand*()\| above as it is guaranteed to never make a
	// system call to generate a new number, except to seed it. This should never
	// be used for cryptographic applications, and is not thread-safe.
	//
	// It is seeded using base::RandUint64() in the constructor, meaning that it
	// doesn't need to be seeded. It can be re-seeded though, with
	// ReseedForTesting(). Its period is long enough that it should not need to be
	// re-seeded during use.
	//
	// Uses the XorShift128+ generator under the hood.
	class BASE_EXPORT InsecureRandomGenerator {
	public:
	// Never use outside testing, not enough entropy.
	void ReseedForTesting(uint64_t seed);

	uint32_t RandUint32();
	uint64_t RandUint64();
	// In [0, 1).
	double RandDouble();

	private:
	InsecureRandomGenerator();
	// State.
	uint64_t a_ = 0, b_ = 0;

	// Before adding a new friend class, make sure that the overhead of
	// base::Rand*() is too high, using something more representative than a
	// microbenchmark.

	// Uses the generator to fill memory pages with random content to make them
	// hard to compress, in a simulation tool not bundled with Chrome. CPU
	// overhead must be minimized to correctly measure memory effects.
	friend class memory_simulator::MemoryHolder;
	// Uses the generator to sub-sample metrics.
	friend class MetricsSubSampler;

	FRIEND_TEST_ALL_PREFIXES(RandUtilTest,
	InsecureRandomGeneratorProducesBothValuesOfAllBits);
	FRIEND_TEST_ALL_PREFIXES(RandUtilTest, InsecureRandomGeneratorChiSquared);
	FRIEND_TEST_ALL_PREFIXES(RandUtilTest, InsecureRandomGeneratorRandDouble);
	FRIEND_TEST_ALL_PREFIXES(RandUtilPerfTest, InsecureRandomRandUint64);
	};

	class BASE_EXPORT MetricsSubSampler {
	public:
	MetricsSubSampler();
	bool ShouldSample(double probability);

	// Disables subsampling in a scope. Useful for testing.
	class BASE_EXPORT ScopedDisableForTesting {
	public:
	ScopedDisableForTesting();
	~ScopedDisableForTesting();
	};

	private:
	InsecureRandomGenerator generator_;
	};

	} // namespace base

	#endif // BASE_RAND_UTIL_H_