| // 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. | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| // ----------------------------------------------------------------------------- | |
| // 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 as detailed below. | |
| // | |
| // 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); | |
| // | |
| // Constructing two `absl::BitGen`s with the same seed sequence in the same | |
| // process will produce the same sequence of variates, but need not do so across | |
| // multiple processes even if they're executing the same binary. | |
| // | |
| // `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. | |
| // | |
| // 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. | |
| // 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, as detailed in the `absl::BitGen` comment. | |
| // | |
| // `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. | |
| // --------------------------------------------------------------------------- | |
| ABSL_NAMESPACE_END | |
| } // namespace absl | |