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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_DISTRIBUTIONS_H_
#define ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_
#include <type_traits>
#include "absl/meta/type_traits.h"
#include "absl/random/internal/distribution_caller.h"
#include "absl/random/internal/traits.h"
#include "absl/random/internal/uniform_helper.h"
namespace absl {
inline namespace lts_2019_08_08 {
namespace random_internal {
template <typename D>
struct DistributionFormatTraits;
// UniformImpl implements the core logic of the Uniform<T> call, which is to
// select the correct distribution type, compute the bounds based on the
// interval tag, and then generate a value.
template <typename NumType, typename TagType, typename URBG>
NumType UniformImpl(TagType tag,
URBG& urbg, // NOLINT(runtime/references)
NumType lo, NumType hi) {
static_assert(
std::is_arithmetic<NumType>::value,
"absl::Uniform<T>() must use an integer or real parameter type.");
using distribution_t =
typename std::conditional<std::is_integral<NumType>::value,
absl::uniform_int_distribution<NumType>,
absl::uniform_real_distribution<NumType>>::type;
using format_t = random_internal::DistributionFormatTraits<distribution_t>;
auto a = random_internal::uniform_lower_bound<NumType>(tag, lo, hi);
auto b = random_internal::uniform_upper_bound<NumType>(tag, lo, hi);
// TODO(lar): it doesn't make a lot of sense to ask for a random number in an
// empty range. Right now we just return a boundary--even though that
// boundary is not an acceptable value! Is there something better we can do
// here?
using gen_t = absl::decay_t<URBG>;
if (a > b) return a;
return DistributionCaller<gen_t>::template Call<distribution_t, format_t>(
&urbg, a, b);
}
// In the absence of an explicitly provided return-type, the template
// "uniform_inferred_return_t<A, B>" is used to derive a suitable type, based on
// the data-types of the endpoint-arguments {A lo, B hi}.
//
// Given endpoints {A lo, B hi}, one of {A, B} will be chosen as the
// return-type, if one type can be implicitly converted into the other, in a
// lossless way. The template "is_widening_convertible" implements the
// compile-time logic for deciding if such a conversion is possible.
//
// If no such conversion between {A, B} exists, then the overload for
// absl::Uniform() will be discarded, and the call will be ill-formed.
// Return-type for absl::Uniform() when the return-type is inferred.
template <typename A, typename B>
using uniform_inferred_return_t =
absl::enable_if_t<absl::disjunction<is_widening_convertible<A, B>,
is_widening_convertible<B, A>>::value,
typename std::conditional<
is_widening_convertible<A, B>::value, B, A>::type>;
} // namespace random_internal
} // inline namespace lts_2019_08_08
} // namespace absl
#endif // ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_
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