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Pods/abseil/absl/random/internal/salted_seed_seq.h

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+// 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 {
+ public:
+  using inner_sequence_type = SSeq;
+  using result_type = typename SSeq::result_type;
+
+  SaltedSeedSeq() : seq_(absl::make_unique<SSeq>()) {}
+
+  template <typename Iterator>
+  SaltedSeedSeq(Iterator begin, Iterator end)
+      : seq_(absl::make_unique<SSeq>(begin, end)) {}
+
+  template <typename T>
+  SaltedSeedSeq(std::initializer_list<T> il)
+      : SaltedSeedSeq(il.begin(), il.end()) {}
+
+  SaltedSeedSeq(const SaltedSeedSeq&) = delete;
+  SaltedSeedSeq& operator=(const SaltedSeedSeq&) = delete;
+
+  SaltedSeedSeq(SaltedSeedSeq&&) = default;
+  SaltedSeedSeq& operator=(SaltedSeedSeq&&) = default;
+
+  template <typename RandomAccessIterator>
+  void generate(RandomAccessIterator begin, RandomAccessIterator end) {
+    using U = typename std::iterator_traits<RandomAccessIterator>::value_type;
+
+    // The common case is that generate is called with ContiguousIterators
+    // to uint arrays. Such contiguous memory regions may be optimized,
+    // which we detect here.
+    using TagType = absl::conditional_t<
+        (std::is_same<U, uint32_t>::value &&
+         (std::is_pointer<RandomAccessIterator>::value ||
+          std::is_same<RandomAccessIterator,
+                       typename std::vector<U>::iterator>::value)),
+        ContiguousAndUint32Tag, DefaultTag>;
+    if (begin != end) {
+      generate_impl(TagType{}, begin, end, std::distance(begin, end));
+    }
+  }
+
+  template <typename OutIterator>
+  void param(OutIterator out) const {
+    seq_->param(out);
+  }
+
+  size_t size() const { return seq_->size(); }
+
+ private:
+  struct ContiguousAndUint32Tag {};
+  struct DefaultTag {};
+
+  // Generate which requires the iterators are contiguous pointers to uint32_t.
+  // Fills the initial seed buffer the underlying SSeq::generate() call,
+  // then mixes in the salt material.
+  template <typename Contiguous>
+  void generate_impl(ContiguousAndUint32Tag, Contiguous begin, Contiguous end,
+                     size_t n) {
+    seq_->generate(begin, end);
+    const uint32_t salt = absl::random_internal::GetSaltMaterial().value_or(0);
+    auto span = absl::Span<uint32_t>(&*begin, n);
+    MixIntoSeedMaterial(absl::MakeConstSpan(&salt, 1), span);
+  }
+
+  // The uncommon case for generate is that it is called with iterators over
+  // some other buffer type which is assignable from a 32-bit value. In this
+  // case we allocate a temporary 32-bit buffer and then copy-assign back
+  // to the initial inputs.
+  template <typename RandomAccessIterator>
+  void generate_impl(DefaultTag, RandomAccessIterator begin,
+                     RandomAccessIterator, size_t n) {
+    // Allocates a seed buffer of `n` elements, generates the seed, then
+    // copies the result into the `out` iterator.
+    absl::InlinedVector<uint32_t, 8> data(n, 0);
+    generate_impl(ContiguousAndUint32Tag{}, data.begin(), data.end(), n);
+    std::copy(data.begin(), data.end(), begin);
+  }
+
+  // Because [rand.req.seedseq] is not required to be copy-constructible,
+  // copy-assignable nor movable, we wrap it with unique pointer to be able
+  // to move SaltedSeedSeq.
+  std::unique_ptr<SSeq> seq_;
+};
+
+// 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 {};
+
+template <typename T>
+struct is_salted_seed_seq<
+    T, typename std::enable_if<std::is_same<
+           T, SaltedSeedSeq<typename T::inner_sequence_type>>::value>::type>
+    : public std::true_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) {
+  return SSeq(std::forward<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) {
+  using sseq_type = typename std::decay<SSeq>::type;
+  using result_type = typename sseq_type::result_type;
+
+  absl::InlinedVector<result_type, 8> data;
+  seq.param(std::back_inserter(data));
+  return SaltedSeedSeq<sseq_type>(data.begin(), data.end());
+}
+
+}  // namespace random_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_