Abseil Common Libraries (C++) (grcp 依赖)
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82 lines
3.5 KiB
82 lines
3.5 KiB
// Copyright 2019 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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#ifndef ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_ |
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#define ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_ |
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#include <type_traits> |
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#include "absl/meta/type_traits.h" |
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#include "absl/random/internal/distribution_caller.h" |
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#include "absl/random/internal/traits.h" |
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#include "absl/random/internal/uniform_helper.h" |
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namespace absl { |
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namespace random_internal { |
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template <typename D> |
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struct DistributionFormatTraits; |
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// UniformImpl implements the core logic of the Uniform<T> call, which is to |
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// select the correct distribution type, compute the bounds based on the |
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// interval tag, and then generate a value. |
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template <typename NumType, typename TagType, typename URBG> |
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NumType UniformImpl(TagType tag, |
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URBG& urbg, // NOLINT(runtime/references) |
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NumType lo, NumType hi) { |
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static_assert( |
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std::is_arithmetic<NumType>::value, |
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"absl::Uniform<T>() must use an integer or real parameter type."); |
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using distribution_t = |
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typename std::conditional<std::is_integral<NumType>::value, |
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absl::uniform_int_distribution<NumType>, |
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absl::uniform_real_distribution<NumType>>::type; |
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using format_t = random_internal::DistributionFormatTraits<distribution_t>; |
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auto a = random_internal::uniform_lower_bound<NumType>(tag, lo, hi); |
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auto b = random_internal::uniform_upper_bound<NumType>(tag, lo, hi); |
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// TODO(lar): it doesn't make a lot of sense to ask for a random number in an |
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// empty range. Right now we just return a boundary--even though that |
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// boundary is not an acceptable value! Is there something better we can do |
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// here? |
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using gen_t = absl::decay_t<URBG>; |
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if (a > b) return a; |
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return DistributionCaller<gen_t>::template Call<distribution_t, format_t>( |
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&urbg, a, b); |
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} |
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// In the absence of an explicitly provided return-type, the template |
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// "uniform_inferred_return_t<A, B>" is used to derive a suitable type, based on |
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// the data-types of the endpoint-arguments {A lo, B hi}. |
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// |
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// Given endpoints {A lo, B hi}, one of {A, B} will be chosen as the |
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// return-type, if one type can be implicitly converted into the other, in a |
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// lossless way. The template "is_widening_convertible" implements the |
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// compile-time logic for deciding if such a conversion is possible. |
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// |
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// If no such conversion between {A, B} exists, then the overload for |
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// absl::Uniform() will be discarded, and the call will be ill-formed. |
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// Return-type for absl::Uniform() when the return-type is inferred. |
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template <typename A, typename B> |
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using uniform_inferred_return_t = |
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absl::enable_if_t<absl::disjunction<is_widening_convertible<A, B>, |
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is_widening_convertible<B, A>>::value, |
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typename std::conditional< |
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is_widening_convertible<A, B>::value, B, A>::type>; |
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} // namespace random_internal |
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} // namespace absl |
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#endif // ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_
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