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Diffstat (limited to 'absl/random/uniform_real_distribution.h')
| -rw-r--r-- | absl/random/uniform_real_distribution.h | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/absl/random/uniform_real_distribution.h b/absl/random/uniform_real_distribution.h new file mode 100644 index 000000000000..600f915b67af --- /dev/null +++ b/absl/random/uniform_real_distribution.h @@ -0,0 +1,193 @@ +// 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: uniform_real_distribution.h +// ----------------------------------------------------------------------------- +// +// This header defines a class for representing a uniform floating-point +// distribution over a half-open interval [a,b). You use this distribution in +// combination with an Abseil random bit generator to produce random values +// according to the rules of the distribution. +// +// `absl::uniform_real_distribution` is a drop-in replacement for the C++11 +// `std::uniform_real_distribution` [rand.dist.uni.real] but is considerably +// faster than the libstdc++ implementation. +// +// Note: the standard-library version may occasionally return `1.0` when +// default-initialized. See https://bugs.llvm.org//show_bug.cgi?id=18767 +// `absl::uniform_real_distribution` does not exhibit this behavior. + +#ifndef ABSL_RANDOM_UNIFORM_REAL_DISTRIBUTION_H_ +#define ABSL_RANDOM_UNIFORM_REAL_DISTRIBUTION_H_ + +#include <cassert> +#include <cmath> +#include <cstdint> +#include <istream> +#include <limits> +#include <type_traits> + +#include "absl/random/internal/distribution_impl.h" +#include "absl/random/internal/fast_uniform_bits.h" +#include "absl/random/internal/iostream_state_saver.h" + +namespace absl { + +// absl::uniform_real_distribution<T> +// +// This distribution produces random floating-point values uniformly distributed +// over the half-open interval [a, b). +// +// Example: +// +// absl::BitGen gen; +// +// // Use the distribution to produce a value between 0.0 (inclusive) +// // and 1.0 (exclusive). +// int value = absl::uniform_real_distribution<double>(0, 1)(gen); +// +template <typename RealType = double> +class uniform_real_distribution { + public: + using result_type = RealType; + + class param_type { + public: + using distribution_type = uniform_real_distribution; + + explicit param_type(result_type lo = 0, result_type hi = 1) + : lo_(lo), hi_(hi), range_(hi - lo) { + // [rand.dist.uni.real] preconditions 2 & 3 + assert(lo <= hi); + // NOTE: For integral types, we can promote the range to an unsigned type, + // which gives full width of the range. However for real (fp) types, this + // is not possible, so value generation cannot use the full range of the + // real type. + assert(range_ <= (std::numeric_limits<result_type>::max)()); + } + + result_type a() const { return lo_; } + result_type b() const { return hi_; } + + friend bool operator==(const param_type& a, const param_type& b) { + return a.lo_ == b.lo_ && a.hi_ == b.hi_; + } + + friend bool operator!=(const param_type& a, const param_type& b) { + return !(a == b); + } + + private: + friend class uniform_real_distribution; + result_type lo_, hi_, range_; + + static_assert(std::is_floating_point<RealType>::value, + "Class-template absl::uniform_real_distribution<> must be " + "parameterized using a floating-point type."); + }; + + uniform_real_distribution() : uniform_real_distribution(0) {} + + explicit uniform_real_distribution(result_type lo, result_type hi = 1) + : param_(lo, hi) {} + + explicit uniform_real_distribution(const param_type& param) : param_(param) {} + + // uniform_real_distribution<T>::reset() + // + // Resets the uniform real distribution. Note that this function has no effect + // because the distribution already produces independent values. + void reset() {} + + template <typename URBG> + result_type operator()(URBG& gen) { // NOLINT(runtime/references) + return operator()(gen, param_); + } + + template <typename URBG> + result_type operator()(URBG& gen, // NOLINT(runtime/references) + const param_type& p); + + result_type a() const { return param_.a(); } + result_type b() const { return param_.b(); } + + param_type param() const { return param_; } + void param(const param_type& params) { param_ = params; } + + result_type(min)() const { return a(); } + result_type(max)() const { return b(); } + + friend bool operator==(const uniform_real_distribution& a, + const uniform_real_distribution& b) { + return a.param_ == b.param_; + } + friend bool operator!=(const uniform_real_distribution& a, + const uniform_real_distribution& b) { + return a.param_ != b.param_; + } + + private: + param_type param_; + random_internal::FastUniformBits<uint64_t> fast_u64_; +}; + +// ----------------------------------------------------------------------------- +// Implementation details follow +// ----------------------------------------------------------------------------- +template <typename RealType> +template <typename URBG> +typename uniform_real_distribution<RealType>::result_type +uniform_real_distribution<RealType>::operator()( + URBG& gen, const param_type& p) { // NOLINT(runtime/references) + using random_internal::PositiveValueT; + while (true) { + const result_type sample = random_internal::RandU64ToReal< + result_type>::template Value<PositiveValueT, true>(fast_u64_(gen)); + const result_type res = p.a() + (sample * p.range_); + if (res < p.b() || p.range_ <= 0 || !std::isfinite(p.range_)) { + return res; + } + // else sample rejected, try again. + } +} + +template <typename CharT, typename Traits, typename RealType> +std::basic_ostream<CharT, Traits>& operator<<( + std::basic_ostream<CharT, Traits>& os, // NOLINT(runtime/references) + const uniform_real_distribution<RealType>& x) { + auto saver = random_internal::make_ostream_state_saver(os); + os.precision(random_internal::stream_precision_helper<RealType>::kPrecision); + os << x.a() << os.fill() << x.b(); + return os; +} + +template <typename CharT, typename Traits, typename RealType> +std::basic_istream<CharT, Traits>& operator>>( + std::basic_istream<CharT, Traits>& is, // NOLINT(runtime/references) + uniform_real_distribution<RealType>& x) { // NOLINT(runtime/references) + using param_type = typename uniform_real_distribution<RealType>::param_type; + using result_type = typename uniform_real_distribution<RealType>::result_type; + auto saver = random_internal::make_istream_state_saver(is); + auto a = random_internal::read_floating_point<result_type>(is); + if (is.fail()) return is; + auto b = random_internal::read_floating_point<result_type>(is); + if (!is.fail()) { + x.param(param_type(a, b)); + } + return is; +} +} // namespace absl + +#endif // ABSL_RANDOM_UNIFORM_REAL_DISTRIBUTION_H_ |