245 lines
9.0 KiB
C++
245 lines
9.0 KiB
C++
// 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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//
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#ifndef ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_
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#define ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_
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#include <cmath>
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#include <limits>
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#include <type_traits>
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#include "absl/base/config.h"
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#include "absl/meta/type_traits.h"
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#include "absl/random/internal/traits.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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template <typename IntType>
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class uniform_int_distribution;
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template <typename RealType>
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class uniform_real_distribution;
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// Interval tag types which specify whether the interval is open or closed
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// on either boundary.
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namespace random_internal {
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template <typename T>
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struct TagTypeCompare {};
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template <typename T>
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constexpr bool operator==(TagTypeCompare<T>, TagTypeCompare<T>) {
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// Tags are mono-states. They always compare equal.
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return true;
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}
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template <typename T>
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constexpr bool operator!=(TagTypeCompare<T>, TagTypeCompare<T>) {
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return false;
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}
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} // namespace random_internal
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struct IntervalClosedClosedTag
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: public random_internal::TagTypeCompare<IntervalClosedClosedTag> {};
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struct IntervalClosedOpenTag
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: public random_internal::TagTypeCompare<IntervalClosedOpenTag> {};
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struct IntervalOpenClosedTag
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: public random_internal::TagTypeCompare<IntervalOpenClosedTag> {};
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struct IntervalOpenOpenTag
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: public random_internal::TagTypeCompare<IntervalOpenOpenTag> {};
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namespace random_internal {
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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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// The functions
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// uniform_lower_bound(tag, a, b)
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// and
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// uniform_upper_bound(tag, a, b)
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// are used as implementation-details for absl::Uniform().
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//
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// Conceptually,
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// [a, b] == [uniform_lower_bound(IntervalClosedClosed, a, b),
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// uniform_upper_bound(IntervalClosedClosed, a, b)]
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// (a, b) == [uniform_lower_bound(IntervalOpenOpen, a, b),
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// uniform_upper_bound(IntervalOpenOpen, a, b)]
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// [a, b) == [uniform_lower_bound(IntervalClosedOpen, a, b),
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// uniform_upper_bound(IntervalClosedOpen, a, b)]
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// (a, b] == [uniform_lower_bound(IntervalOpenClosed, a, b),
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// uniform_upper_bound(IntervalOpenClosed, a, b)]
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//
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template <typename IntType, typename Tag>
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typename absl::enable_if_t<
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absl::conjunction<
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std::is_integral<IntType>,
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absl::disjunction<std::is_same<Tag, IntervalOpenClosedTag>,
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std::is_same<Tag, IntervalOpenOpenTag>>>::value,
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IntType>
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uniform_lower_bound(Tag, IntType a, IntType) {
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return a < (std::numeric_limits<IntType>::max)() ? (a + 1) : a;
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}
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template <typename FloatType, typename Tag>
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typename absl::enable_if_t<
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absl::conjunction<
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std::is_floating_point<FloatType>,
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absl::disjunction<std::is_same<Tag, IntervalOpenClosedTag>,
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std::is_same<Tag, IntervalOpenOpenTag>>>::value,
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FloatType>
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uniform_lower_bound(Tag, FloatType a, FloatType b) {
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return std::nextafter(a, b);
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}
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template <typename NumType, typename Tag>
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typename absl::enable_if_t<
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absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
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std::is_same<Tag, IntervalClosedOpenTag>>::value,
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NumType>
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uniform_lower_bound(Tag, NumType a, NumType) {
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return a;
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}
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template <typename IntType, typename Tag>
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typename absl::enable_if_t<
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absl::conjunction<
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std::is_integral<IntType>,
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absl::disjunction<std::is_same<Tag, IntervalClosedOpenTag>,
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std::is_same<Tag, IntervalOpenOpenTag>>>::value,
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IntType>
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uniform_upper_bound(Tag, IntType, IntType b) {
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return b > (std::numeric_limits<IntType>::min)() ? (b - 1) : b;
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}
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template <typename FloatType, typename Tag>
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typename absl::enable_if_t<
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absl::conjunction<
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std::is_floating_point<FloatType>,
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absl::disjunction<std::is_same<Tag, IntervalClosedOpenTag>,
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std::is_same<Tag, IntervalOpenOpenTag>>>::value,
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FloatType>
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uniform_upper_bound(Tag, FloatType, FloatType b) {
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return b;
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}
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template <typename IntType, typename Tag>
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typename absl::enable_if_t<
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absl::conjunction<
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std::is_integral<IntType>,
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absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
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std::is_same<Tag, IntervalOpenClosedTag>>>::value,
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IntType>
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uniform_upper_bound(Tag, IntType, IntType b) {
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return b;
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}
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template <typename FloatType, typename Tag>
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typename absl::enable_if_t<
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absl::conjunction<
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std::is_floating_point<FloatType>,
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absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
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std::is_same<Tag, IntervalOpenClosedTag>>>::value,
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FloatType>
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uniform_upper_bound(Tag, FloatType, FloatType b) {
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return std::nextafter(b, (std::numeric_limits<FloatType>::max)());
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}
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// Returns whether the bounds are valid for the underlying distribution.
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// Inputs must have already been resolved via uniform_*_bound calls.
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//
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// The c++ standard constraints in [rand.dist.uni.int] are listed as:
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// requires: lo <= hi.
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//
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// In the uniform_int_distrubtion, {lo, hi} are closed, closed. Thus:
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// [0, 0] is legal.
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// [0, 0) is not legal, but [0, 1) is, which translates to [0, 0].
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// (0, 1) is not legal, but (0, 2) is, which translates to [1, 1].
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// (0, 0] is not legal, but (0, 1] is, which translates to [1, 1].
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//
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// The c++ standard constraints in [rand.dist.uni.real] are listed as:
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// requires: lo <= hi.
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// requires: (hi - lo) <= numeric_limits<T>::max()
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//
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// In the uniform_real_distribution, {lo, hi} are closed, open, Thus:
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// [0, 0] is legal, which is [0, 0+epsilon).
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// [0, 0) is legal.
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// (0, 0) is not legal, but (0-epsilon, 0+epsilon) is.
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// (0, 0] is not legal, but (0, 0+epsilon] is.
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//
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template <typename FloatType>
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absl::enable_if_t<std::is_floating_point<FloatType>::value, bool>
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is_uniform_range_valid(FloatType a, FloatType b) {
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return a <= b && std::isfinite(b - a);
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}
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template <typename IntType>
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absl::enable_if_t<std::is_integral<IntType>::value, bool>
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is_uniform_range_valid(IntType a, IntType b) {
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return a <= b;
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}
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// UniformDistribution selects either absl::uniform_int_distribution
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// or absl::uniform_real_distribution depending on the NumType parameter.
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template <typename NumType>
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using UniformDistribution =
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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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// UniformDistributionWrapper is used as the underlying distribution type
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// by the absl::Uniform template function. It selects the proper Abseil
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// uniform distribution and provides constructor overloads that match the
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// expected parameter order as well as adjusting distribtuion bounds based
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// on the tag.
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template <typename NumType>
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struct UniformDistributionWrapper : public UniformDistribution<NumType> {
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template <typename TagType>
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explicit UniformDistributionWrapper(TagType, NumType lo, NumType hi)
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: UniformDistribution<NumType>(
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uniform_lower_bound<NumType>(TagType{}, lo, hi),
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uniform_upper_bound<NumType>(TagType{}, lo, hi)) {}
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explicit UniformDistributionWrapper(NumType lo, NumType hi)
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: UniformDistribution<NumType>(
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uniform_lower_bound<NumType>(IntervalClosedOpenTag(), lo, hi),
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uniform_upper_bound<NumType>(IntervalClosedOpenTag(), lo, hi)) {}
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explicit UniformDistributionWrapper()
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: UniformDistribution<NumType>(std::numeric_limits<NumType>::lowest(),
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(std::numeric_limits<NumType>::max)()) {}
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};
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} // namespace random_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_
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