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Diffstat (limited to 'third_party/abseil_cpp/absl/random/internal/randen_engine.h')
-rw-r--r-- | third_party/abseil_cpp/absl/random/internal/randen_engine.h | 230 |
1 files changed, 0 insertions, 230 deletions
diff --git a/third_party/abseil_cpp/absl/random/internal/randen_engine.h b/third_party/abseil_cpp/absl/random/internal/randen_engine.h deleted file mode 100644 index 6b33731336e7..000000000000 --- a/third_party/abseil_cpp/absl/random/internal/randen_engine.h +++ /dev/null @@ -1,230 +0,0 @@ -// 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_RANDEN_ENGINE_H_ -#define ABSL_RANDOM_INTERNAL_RANDEN_ENGINE_H_ - -#include <algorithm> -#include <cinttypes> -#include <cstdlib> -#include <iostream> -#include <iterator> -#include <limits> -#include <type_traits> - -#include "absl/meta/type_traits.h" -#include "absl/random/internal/iostream_state_saver.h" -#include "absl/random/internal/randen.h" - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace random_internal { - -// Deterministic pseudorandom byte generator with backtracking resistance -// (leaking the state does not compromise prior outputs). Based on Reverie -// (see "A Robust and Sponge-Like PRNG with Improved Efficiency") instantiated -// with an improved Simpira-like permutation. -// Returns values of type "T" (must be a built-in unsigned integer type). -// -// RANDen = RANDom generator or beetroots in Swiss High German. -// 'Strong' (well-distributed, unpredictable, backtracking-resistant) random -// generator, faster in some benchmarks than std::mt19937_64 and pcg64_c32. -template <typename T> -class alignas(16) randen_engine { - public: - // C++11 URBG interface: - using result_type = T; - static_assert(std::is_unsigned<result_type>::value, - "randen_engine template argument must be a built-in unsigned " - "integer type"); - - static constexpr result_type(min)() { - return (std::numeric_limits<result_type>::min)(); - } - - static constexpr result_type(max)() { - return (std::numeric_limits<result_type>::max)(); - } - - explicit randen_engine(result_type seed_value = 0) { seed(seed_value); } - - template <class SeedSequence, - typename = typename absl::enable_if_t< - !std::is_same<SeedSequence, randen_engine>::value>> - explicit randen_engine(SeedSequence&& seq) { - seed(seq); - } - - randen_engine(const randen_engine&) = default; - - // Returns random bits from the buffer in units of result_type. - result_type operator()() { - // Refill the buffer if needed (unlikely). - if (next_ >= kStateSizeT) { - next_ = kCapacityT; - impl_.Generate(state_); - } - - return state_[next_++]; - } - - template <class SeedSequence> - typename absl::enable_if_t< - !std::is_convertible<SeedSequence, result_type>::value> - seed(SeedSequence&& seq) { - // Zeroes the state. - seed(); - reseed(seq); - } - - void seed(result_type seed_value = 0) { - next_ = kStateSizeT; - // Zeroes the inner state and fills the outer state with seed_value to - // mimics behaviour of reseed - std::fill(std::begin(state_), std::begin(state_) + kCapacityT, 0); - std::fill(std::begin(state_) + kCapacityT, std::end(state_), seed_value); - } - - // Inserts entropy into (part of) the state. Calling this periodically with - // sufficient entropy ensures prediction resistance (attackers cannot predict - // future outputs even if state is compromised). - template <class SeedSequence> - void reseed(SeedSequence& seq) { - using sequence_result_type = typename SeedSequence::result_type; - static_assert(sizeof(sequence_result_type) == 4, - "SeedSequence::result_type must be 32-bit"); - - constexpr size_t kBufferSize = - Randen::kSeedBytes / sizeof(sequence_result_type); - alignas(16) sequence_result_type buffer[kBufferSize]; - - // Randen::Absorb XORs the seed into state, which is then mixed by a call - // to Randen::Generate. Seeding with only the provided entropy is preferred - // to using an arbitrary generate() call, so use [rand.req.seed_seq] - // size as a proxy for the number of entropy units that can be generated - // without relying on seed sequence mixing... - const size_t entropy_size = seq.size(); - if (entropy_size < kBufferSize) { - // ... and only request that many values, or 256-bits, when unspecified. - const size_t requested_entropy = (entropy_size == 0) ? 8u : entropy_size; - std::fill(std::begin(buffer) + requested_entropy, std::end(buffer), 0); - seq.generate(std::begin(buffer), std::begin(buffer) + requested_entropy); - // The Randen paper suggests preferentially initializing even-numbered - // 128-bit vectors of the randen state (there are 16 such vectors). - // The seed data is merged into the state offset by 128-bits, which - // implies prefering seed bytes [16..31, ..., 208..223]. Since the - // buffer is 32-bit values, we swap the corresponding buffer positions in - // 128-bit chunks. - size_t dst = kBufferSize; - while (dst > 7) { - // leave the odd bucket as-is. - dst -= 4; - size_t src = dst >> 1; - // swap 128-bits into the even bucket - std::swap(buffer[--dst], buffer[--src]); - std::swap(buffer[--dst], buffer[--src]); - std::swap(buffer[--dst], buffer[--src]); - std::swap(buffer[--dst], buffer[--src]); - } - } else { - seq.generate(std::begin(buffer), std::end(buffer)); - } - impl_.Absorb(buffer, state_); - - // Generate will be called when operator() is called - next_ = kStateSizeT; - } - - void discard(uint64_t count) { - uint64_t step = std::min<uint64_t>(kStateSizeT - next_, count); - count -= step; - - constexpr uint64_t kRateT = kStateSizeT - kCapacityT; - while (count > 0) { - next_ = kCapacityT; - impl_.Generate(state_); - step = std::min<uint64_t>(kRateT, count); - count -= step; - } - next_ += step; - } - - bool operator==(const randen_engine& other) const { - return next_ == other.next_ && - std::equal(std::begin(state_), std::end(state_), - std::begin(other.state_)); - } - - bool operator!=(const randen_engine& other) const { - return !(*this == other); - } - - template <class CharT, class Traits> - friend std::basic_ostream<CharT, Traits>& operator<<( - std::basic_ostream<CharT, Traits>& os, // NOLINT(runtime/references) - const randen_engine<T>& engine) { // NOLINT(runtime/references) - using numeric_type = - typename random_internal::stream_format_type<result_type>::type; - auto saver = random_internal::make_ostream_state_saver(os); - for (const auto& elem : engine.state_) { - // In the case that `elem` is `uint8_t`, it must be cast to something - // larger so that it prints as an integer rather than a character. For - // simplicity, apply the cast all circumstances. - os << static_cast<numeric_type>(elem) << os.fill(); - } - os << engine.next_; - return os; - } - - template <class CharT, class Traits> - friend std::basic_istream<CharT, Traits>& operator>>( - std::basic_istream<CharT, Traits>& is, // NOLINT(runtime/references) - randen_engine<T>& engine) { // NOLINT(runtime/references) - using numeric_type = - typename random_internal::stream_format_type<result_type>::type; - result_type state[kStateSizeT]; - size_t next; - for (auto& elem : state) { - // It is not possible to read uint8_t from wide streams, so it is - // necessary to read a wider type and then cast it to uint8_t. - numeric_type value; - is >> value; - elem = static_cast<result_type>(value); - } - is >> next; - if (is.fail()) { - return is; - } - std::memcpy(engine.state_, state, sizeof(engine.state_)); - engine.next_ = next; - return is; - } - - private: - static constexpr size_t kStateSizeT = - Randen::kStateBytes / sizeof(result_type); - static constexpr size_t kCapacityT = - Randen::kCapacityBytes / sizeof(result_type); - - // First kCapacityT are `inner', the others are accessible random bits. - alignas(16) result_type state_[kStateSizeT]; - size_t next_; // index within state_ - Randen impl_; -}; - -} // namespace random_internal -ABSL_NAMESPACE_END -} // namespace absl - -#endif // ABSL_RANDOM_INTERNAL_RANDEN_ENGINE_H_ |