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Diffstat (limited to 'absl/random/random.h')
| -rw-r--r-- | absl/random/random.h | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/absl/random/random.h b/absl/random/random.h new file mode 100644 index 000000000000..dc6852f4adf3 --- /dev/null +++ b/absl/random/random.h @@ -0,0 +1,187 @@ +// Copyright 2017 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +// +// ----------------------------------------------------------------------------- +// File: random.h +// ----------------------------------------------------------------------------- +// +// This header defines the recommended Uniform Random Bit Generator (URBG) +// types for use within the Abseil Random library. These types are not +// suitable for security-related use-cases, but should suffice for most other +// uses of generating random values. +// +// The Abseil random library provides the following URBG types: +// +// * BitGen, a good general-purpose bit generator, optimized for generating +// random (but not cryptographically secure) values +// * InsecureBitGen, a slightly faster, though less random, bit generator, for +// cases where the existing BitGen is a drag on performance. + +#ifndef ABSL_RANDOM_RANDOM_H_ +#define ABSL_RANDOM_RANDOM_H_ + +#include <random> + +#include "absl/random/distributions.h" // IWYU pragma: export +#include "absl/random/internal/nonsecure_base.h" // IWYU pragma: export +#include "absl/random/internal/pcg_engine.h" // IWYU pragma: export +#include "absl/random/internal/pool_urbg.h" +#include "absl/random/internal/randen_engine.h" +#include "absl/random/seed_sequences.h" // IWYU pragma: export + +namespace absl { + +// ----------------------------------------------------------------------------- +// absl::BitGen +// ----------------------------------------------------------------------------- +// +// `absl::BitGen` is a general-purpose random bit generator for generating +// random values for use within the Abseil random library. Typically, you use a +// bit generator in combination with a distribution to provide random values. +// +// Example: +// +// // Create an absl::BitGen. There is no need to seed this bit generator. +// absl::BitGen gen; +// +// // Generate an integer value in the closed interval [1,6] +// int die_roll = absl::uniform_int_distribution<int>(1, 6)(gen); +// +// `absl::BitGen` is seeded by default with non-deterministic data to produce +// different sequences of random values across different instances, including +// different binary invocations. This behavior is different than the standard +// library bit generators, which use golden values as their seeds. Default +// construction intentionally provides no stability guarantees, to avoid +// accidental dependence on such a property. +// +// `absl::BitGen` may be constructed with an optional seed sequence type, +// conforming to [rand.req.seed_seq], which will be mixed with additional +// non-deterministic data. +// +// Example: +// +// // Create an absl::BitGen using an std::seed_seq seed sequence +// std::seed_seq seq{1,2,3}; +// absl::BitGen gen_with_seed(seq); +// +// // Generate an integer value in the closed interval [1,6] +// int die_roll2 = absl::uniform_int_distribution<int>(1, 6)(gen_with_seed); +// +// `absl::BitGen` meets the requirements of the Uniform Random Bit Generator +// (URBG) concept as per the C++17 standard [rand.req.urng] though differs +// slightly with [rand.req.eng]. Like its standard library equivalents (e.g. +// `std::mersenne_twister_engine`) `absl::BitGen` is not cryptographically +// secure. +// +// Constructing two `absl::BitGen`s with the same seed sequence in the same +// binary will produce the same sequence of variates within the same binary, but +// need not do so across multiple binary invocations. +// +// This type has been optimized to perform better than Mersenne Twister +// (https://en.wikipedia.org/wiki/Mersenne_Twister) and many other complex URBG +// types on modern x86, ARM, and PPC architectures. +// +// This type is thread-compatible, but not thread-safe. + +// --------------------------------------------------------------------------- +// absl::BitGen member functions +// --------------------------------------------------------------------------- + +// absl::BitGen::operator()() +// +// Calls the BitGen, returning a generated value. + +// absl::BitGen::min() +// +// Returns the smallest possible value from this bit generator. + +// absl::BitGen::max() +// +// Returns the largest possible value from this bit generator., and + +// absl::BitGen::discard(num) +// +// Advances the internal state of this bit generator by `num` times, and +// discards the intermediate results. +// --------------------------------------------------------------------------- + +using BitGen = random_internal::NonsecureURBGBase< + random_internal::randen_engine<uint64_t>>; + +// ----------------------------------------------------------------------------- +// absl::InsecureBitGen +// ----------------------------------------------------------------------------- +// +// `absl::InsecureBitGen` is an efficient random bit generator for generating +// random values, recommended only for performance-sensitive use cases where +// `absl::BitGen` is not satisfactory when compute-bounded by bit generation +// costs. +// +// Example: +// +// // Create an absl::InsecureBitGen +// absl::InsecureBitGen gen; +// for (size_t i = 0; i < 1000000; i++) { +// +// // Generate a bunch of random values from some complex distribution +// auto my_rnd = some_distribution(gen, 1, 1000); +// } +// +// Like `absl::BitGen`, `absl::InsecureBitGen` is seeded by default with +// non-deterministic data to produce different sequences of random values across +// different instances, including different binary invocations. (This behavior +// is different than the standard library bit generators, which use golden +// values as their seeds.) +// +// `absl::InsecureBitGen` may be constructed with an optional seed sequence +// type, conforming to [rand.req.seed_seq], which will be mixed with additional +// non-deterministic data. (See std_seed_seq.h for more information.) +// +// `absl::InsecureBitGen` meets the requirements of the Uniform Random Bit +// Generator (URBG) concept as per the C++17 standard [rand.req.urng] though +// its implementation differs slightly with [rand.req.eng]. Like its standard +// library equivalents (e.g. `std::mersenne_twister_engine`) +// `absl::InsecureBitGen` is not cryptographically secure. +// +// Prefer `absl::BitGen` over `absl::InsecureBitGen` as the general type is +// often fast enough for the vast majority of applications. + +using InsecureBitGen = + random_internal::NonsecureURBGBase<random_internal::pcg64_2018_engine>; + +// --------------------------------------------------------------------------- +// absl::InsecureBitGen member functions +// --------------------------------------------------------------------------- + +// absl::InsecureBitGen::operator()() +// +// Calls the InsecureBitGen, returning a generated value. + +// absl::InsecureBitGen::min() +// +// Returns the smallest possible value from this bit generator. + +// absl::InsecureBitGen::max() +// +// Returns the largest possible value from this bit generator. + +// absl::InsecureBitGen::discard(num) +// +// Advances the internal state of this bit generator by `num` times, and +// discards the intermediate results. +// --------------------------------------------------------------------------- + +} // namespace absl + +#endif // ABSL_RANDOM_RANDOM_H_ |