explicit_seed_seq.h (2887B)
1 // Copyright 2017 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef ABSL_RANDOM_INTERNAL_EXPLICIT_SEED_SEQ_H_ 16 #define ABSL_RANDOM_INTERNAL_EXPLICIT_SEED_SEQ_H_ 17 18 #include <algorithm> 19 #include <cstddef> 20 #include <cstdint> 21 #include <initializer_list> 22 #include <iterator> 23 #include <vector> 24 25 #include "absl/base/config.h" 26 #include "absl/base/internal/endian.h" 27 28 namespace absl { 29 ABSL_NAMESPACE_BEGIN 30 namespace random_internal { 31 32 // This class conforms to the C++ Standard "Seed Sequence" concept 33 // [rand.req.seedseq]. 34 // 35 // An "ExplicitSeedSeq" is meant to provide a conformant interface for 36 // forwarding pre-computed seed material to the constructor of a class 37 // conforming to the "Uniform Random Bit Generator" concept. This class makes no 38 // attempt to mutate the state provided by its constructor, and returns it 39 // directly via ExplicitSeedSeq::generate(). 40 // 41 // If this class is asked to generate more seed material than was provided to 42 // the constructor, then the remaining bytes will be filled with deterministic, 43 // nonrandom data. 44 class ExplicitSeedSeq { 45 public: 46 using result_type = uint32_t; 47 48 ExplicitSeedSeq() : state_() {} 49 50 // Copy and move both allowed. 51 ExplicitSeedSeq(const ExplicitSeedSeq& other) = default; 52 ExplicitSeedSeq& operator=(const ExplicitSeedSeq& other) = default; 53 ExplicitSeedSeq(ExplicitSeedSeq&& other) = default; 54 ExplicitSeedSeq& operator=(ExplicitSeedSeq&& other) = default; 55 56 template <typename Iterator> 57 ExplicitSeedSeq(Iterator begin, Iterator end) { 58 for (auto it = begin; it != end; it++) { 59 state_.push_back(*it & 0xffffffff); 60 } 61 } 62 63 template <typename T> 64 ExplicitSeedSeq(std::initializer_list<T> il) 65 : ExplicitSeedSeq(il.begin(), il.end()) {} 66 67 size_t size() const { return state_.size(); } 68 69 template <typename OutIterator> 70 void param(OutIterator out) const { 71 std::copy(std::begin(state_), std::end(state_), out); 72 } 73 74 template <typename OutIterator> 75 void generate(OutIterator begin, OutIterator end) { 76 for (size_t index = 0; begin != end; begin++) { 77 *begin = state_.empty() ? 0 : state_[index++]; 78 if (index >= state_.size()) { 79 index = 0; 80 } 81 } 82 } 83 84 protected: 85 std::vector<uint32_t> state_; 86 }; 87 88 } // namespace random_internal 89 ABSL_NAMESPACE_END 90 } // namespace absl 91 92 #endif // ABSL_RANDOM_INTERNAL_EXPLICIT_SEED_SEQ_H_