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// 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_