chromium/third_party/abseil-cpp/absl/random/internal/salted_seed_seq.h

// 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.

#ifndef ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_
#define ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_

#include <cstdint>
#include <cstdlib>
#include <initializer_list>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>

#include "absl/container/inlined_vector.h"
#include "absl/meta/type_traits.h"
#include "absl/random/internal/seed_material.h"
#include "absl/types/optional.h"
#include "absl/types/span.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {

// This class conforms to the C++ Standard "Seed Sequence" concept
// [rand.req.seedseq].
//
// A `SaltedSeedSeq` is meant to wrap an existing seed sequence and modify
// generated sequence by mixing with extra entropy. This entropy may be
// build-dependent or process-dependent. The implementation may change to be
// have either or both kinds of entropy. If salt is not available sequence is
// not modified.
template <typename SSeq>
class SaltedSeedSeq { … };

// is_salted_seed_seq indicates whether the type is a SaltedSeedSeq.
template <typename T, typename = void>
struct is_salted_seed_seq : public std::false_type { … };

is_salted_seed_seq<T, typename std::enable_if<std::is_same<T, SaltedSeedSeq<typename T::inner_sequence_type>>::value>::type>;

// MakeSaltedSeedSeq returns a salted variant of the seed sequence.
// When provided with an existing SaltedSeedSeq, returns the input parameter,
// otherwise constructs a new SaltedSeedSeq which embodies the original
// non-salted seed parameters.
template <
    typename SSeq,  //
    typename EnableIf = absl::enable_if_t<is_salted_seed_seq<SSeq>::value>>
SSeq MakeSaltedSeedSeq(SSeq&& seq) { … }

template <
    typename SSeq,  //
    typename EnableIf = absl::enable_if_t<!is_salted_seed_seq<SSeq>::value>>
SaltedSeedSeq<typename std::decay<SSeq>::type> MakeSaltedSeedSeq(SSeq&& seq) { … }

}  // namespace random_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_