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 27 namespace absl { 28 ABSL_NAMESPACE_BEGIN 29 namespace random_internal { 30 31 // This class conforms to the C++ Standard "Seed Sequence" concept 32 // [rand.req.seedseq]. 33 // 34 // An "ExplicitSeedSeq" is meant to provide a conformant interface for 35 // forwarding pre-computed seed material to the constructor of a class 36 // conforming to the "Uniform Random Bit Generator" concept. This class makes no 37 // attempt to mutate the state provided by its constructor, and returns it 38 // directly via ExplicitSeedSeq::generate(). 39 // 40 // If this class is asked to generate more seed material than was provided to 41 // the constructor, then the remaining bytes will be filled with deterministic, 42 // nonrandom data. 43 class ExplicitSeedSeq { 44 public: 45 using result_type = uint32_t; 46 ExplicitSeedSeq()47 ExplicitSeedSeq() : state_() {} 48 49 // Copy and move both allowed. 50 ExplicitSeedSeq(const ExplicitSeedSeq& other) = default; 51 ExplicitSeedSeq& operator=(const ExplicitSeedSeq& other) = default; 52 ExplicitSeedSeq(ExplicitSeedSeq&& other) = default; 53 ExplicitSeedSeq& operator=(ExplicitSeedSeq&& other) = default; 54 55 template <typename Iterator> ExplicitSeedSeq(Iterator begin,Iterator end)56 ExplicitSeedSeq(Iterator begin, Iterator end) { 57 for (auto it = begin; it != end; it++) { 58 state_.push_back(*it & 0xffffffff); 59 } 60 } 61 62 template <typename T> ExplicitSeedSeq(std::initializer_list<T> il)63 ExplicitSeedSeq(std::initializer_list<T> il) 64 : ExplicitSeedSeq(il.begin(), il.end()) {} 65 size()66 size_t size() const { return state_.size(); } 67 68 template <typename OutIterator> param(OutIterator out)69 void param(OutIterator out) const { 70 std::copy(std::begin(state_), std::end(state_), out); 71 } 72 73 template <typename OutIterator> generate(OutIterator begin,OutIterator end)74 void generate(OutIterator begin, OutIterator end) { 75 for (size_t index = 0; begin != end; begin++) { 76 *begin = state_.empty() ? 0 : state_[index++]; 77 if (index >= state_.size()) { 78 index = 0; 79 } 80 } 81 } 82 83 protected: 84 std::vector<uint32_t> state_; 85 }; 86 87 } // namespace random_internal 88 ABSL_NAMESPACE_END 89 } // namespace absl 90 91 #endif // ABSL_RANDOM_INTERNAL_EXPLICIT_SEED_SEQ_H_ 92