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// Copyright 2019 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.
//
#ifndef ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_
#define ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_
#include <cmath>
#include <limits>
#include <type_traits>
#include "absl/meta/type_traits.h"
namespace absl {
template <typename IntType>
class uniform_int_distribution;
template <typename RealType>
class uniform_real_distribution;
// Interval tag types which specify whether the interval is open or closed
// on either boundary.
namespace random_internal {
template <typename T>
struct TagTypeCompare {};
template <typename T>
constexpr bool operator==(TagTypeCompare<T>, TagTypeCompare<T>) {
// Tags are mono-states. They always compare equal.
return true;
}
template <typename T>
constexpr bool operator!=(TagTypeCompare<T>, TagTypeCompare<T>) {
return false;
}
} // namespace random_internal
struct IntervalClosedClosedTag
: public random_internal::TagTypeCompare<IntervalClosedClosedTag> {};
struct IntervalClosedOpenTag
: public random_internal::TagTypeCompare<IntervalClosedOpenTag> {};
struct IntervalOpenClosedTag
: public random_internal::TagTypeCompare<IntervalOpenClosedTag> {};
struct IntervalOpenOpenTag
: public random_internal::TagTypeCompare<IntervalOpenOpenTag> {};
namespace random_internal {
// The functions
// uniform_lower_bound(tag, a, b)
// and
// uniform_upper_bound(tag, a, b)
// are used as implementation-details for absl::Uniform().
//
// Conceptually,
// [a, b] == [uniform_lower_bound(IntervalClosedClosed, a, b),
// uniform_upper_bound(IntervalClosedClosed, a, b)]
// (a, b) == [uniform_lower_bound(IntervalOpenOpen, a, b),
// uniform_upper_bound(IntervalOpenOpen, a, b)]
// [a, b) == [uniform_lower_bound(IntervalClosedOpen, a, b),
// uniform_upper_bound(IntervalClosedOpen, a, b)]
// (a, b] == [uniform_lower_bound(IntervalOpenClosed, a, b),
// uniform_upper_bound(IntervalOpenClosed, a, b)]
//
template <typename IntType, typename Tag>
typename absl::enable_if_t<
absl::conjunction<
std::is_integral<IntType>,
absl::disjunction<std::is_same<Tag, IntervalOpenClosedTag>,
std::is_same<Tag, IntervalOpenOpenTag>>>::value,
IntType>
uniform_lower_bound(Tag, IntType a, IntType) {
return a + 1;
}
template <typename FloatType, typename Tag>
typename absl::enable_if_t<
absl::conjunction<
std::is_floating_point<FloatType>,
absl::disjunction<std::is_same<Tag, IntervalOpenClosedTag>,
std::is_same<Tag, IntervalOpenOpenTag>>>::value,
FloatType>
uniform_lower_bound(Tag, FloatType a, FloatType b) {
return std::nextafter(a, b);
}
template <typename NumType, typename Tag>
typename absl::enable_if_t<
absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
std::is_same<Tag, IntervalClosedOpenTag>>::value,
NumType>
uniform_lower_bound(Tag, NumType a, NumType) {
return a;
}
template <typename IntType, typename Tag>
typename absl::enable_if_t<
absl::conjunction<
std::is_integral<IntType>,
absl::disjunction<std::is_same<Tag, IntervalClosedOpenTag>,
std::is_same<Tag, IntervalOpenOpenTag>>>::value,
IntType>
uniform_upper_bound(Tag, IntType, IntType b) {
return b - 1;
}
template <typename FloatType, typename Tag>
typename absl::enable_if_t<
absl::conjunction<
std::is_floating_point<FloatType>,
absl::disjunction<std::is_same<Tag, IntervalClosedOpenTag>,
std::is_same<Tag, IntervalOpenOpenTag>>>::value,
FloatType>
uniform_upper_bound(Tag, FloatType, FloatType b) {
return b;
}
template <typename IntType, typename Tag>
typename absl::enable_if_t<
absl::conjunction<
std::is_integral<IntType>,
absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
std::is_same<Tag, IntervalOpenClosedTag>>>::value,
IntType>
uniform_upper_bound(Tag, IntType, IntType b) {
return b;
}
template <typename FloatType, typename Tag>
typename absl::enable_if_t<
absl::conjunction<
std::is_floating_point<FloatType>,
absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
std::is_same<Tag, IntervalOpenClosedTag>>>::value,
FloatType>
uniform_upper_bound(Tag, FloatType, FloatType b) {
return std::nextafter(b, (std::numeric_limits<FloatType>::max)());
}
template <typename NumType>
using UniformDistribution =
typename std::conditional<std::is_integral<NumType>::value,
absl::uniform_int_distribution<NumType>,
absl::uniform_real_distribution<NumType>>::type;
template <typename TagType, typename NumType>
struct UniformDistributionWrapper : public UniformDistribution<NumType> {
explicit UniformDistributionWrapper(TagType, NumType lo, NumType hi)
: UniformDistribution<NumType>(
uniform_lower_bound<NumType>(TagType{}, lo, hi),
uniform_upper_bound<NumType>(TagType{}, lo, hi)) {}
};
} // namespace random_internal
} // namespace absl
#endif // ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_
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