12bc53e031
-- c99f979ad34f155fbeeea69b88bdc7458d89a21c by Derek Mauro <dmauro@google.com>: Remove a floating point division by zero test. This isn't testing behavior related to the library, and MSVC warns about it in opt mode. PiperOrigin-RevId: 285220804 -- 68b015491f0dbf1ab547994673281abd1f34cd4b by Gennadiy Rozental <rogeeff@google.com>: This CL introduces following changes to the class FlagImpl: * We eliminate the CommandLineFlagLocks struct. Instead callback guard and callback function are combined into a single CallbackData struct, while primary data lock is stored separately. * CallbackData member of class FlagImpl is initially set to be nullptr and is only allocated and initialized when a flag's callback is being set. For most flags we do not pay for the extra space and extra absl::Mutex now. * Primary data guard is stored in data_guard_ data member. This is a properly aligned character buffer of necessary size. During initialization of the flag we construct absl::Mutex in this space using placement new call. * We now avoid extra value copy after successful attempt to parse value out of string. Instead we swap flag's current value with tentative value we just produced. PiperOrigin-RevId: 285132636 -- ed45d118fb818969eb13094cf7827c885dfc562c by Tom Manshreck <shreck@google.com>: Change null-term* (and nul-term*) to NUL-term* in comments PiperOrigin-RevId: 285036610 -- 729619017944db895ce8d6d29c1995aa2e5628a5 by Derek Mauro <dmauro@google.com>: Use the Posix implementation of thread identity on MinGW. Some versions of MinGW suffer from thread_local bugs. PiperOrigin-RevId: 285022920 -- 39a25493503c76885bc3254c28f66a251c5b5bb0 by Greg Falcon <gfalcon@google.com>: Implementation detail change. Add further ABSL_NAMESPACE_BEGIN and _END annotation macros to files in Abseil. PiperOrigin-RevId: 285012012 GitOrigin-RevId: c99f979ad34f155fbeeea69b88bdc7458d89a21c Change-Id: I4c85d3704e45d11a9ac50d562f39640a6adbedc1
110 lines
4.1 KiB
C++
110 lines
4.1 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// File: seed_sequences.h
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// -----------------------------------------------------------------------------
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//
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// This header contains utilities for creating and working with seed sequences
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// conforming to [rand.req.seedseq]. In general, direct construction of seed
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// sequences is discouraged, but use-cases for construction of identical bit
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// generators (using the same seed sequence) may be helpful (e.g. replaying a
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// simulation whose state is derived from variates of a bit generator).
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#ifndef ABSL_RANDOM_SEED_SEQUENCES_H_
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#define ABSL_RANDOM_SEED_SEQUENCES_H_
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#include <iterator>
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#include <random>
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#include "absl/random/internal/salted_seed_seq.h"
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#include "absl/random/internal/seed_material.h"
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#include "absl/random/seed_gen_exception.h"
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#include "absl/types/span.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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// -----------------------------------------------------------------------------
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// absl::SeedSeq
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// -----------------------------------------------------------------------------
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//
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// `absl::SeedSeq` constructs a seed sequence according to [rand.req.seedseq]
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// for use within bit generators. `absl::SeedSeq`, unlike `std::seed_seq`
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// additionally salts the generated seeds with extra implementation-defined
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// entropy. For that reason, you can use `absl::SeedSeq` in combination with
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// standard library bit generators (e.g. `std::mt19937`) to introduce
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// non-determinism in your seeds.
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//
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// Example:
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//
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// absl::SeedSeq my_seed_seq({a, b, c});
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// std::mt19937 my_bitgen(my_seed_seq);
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//
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using SeedSeq = random_internal::SaltedSeedSeq<std::seed_seq>;
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// -----------------------------------------------------------------------------
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// absl::CreateSeedSeqFrom(bitgen*)
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// -----------------------------------------------------------------------------
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//
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// Constructs a seed sequence conforming to [rand.req.seedseq] using variates
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// produced by a provided bit generator.
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//
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// You should generally avoid direct construction of seed sequences, but
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// use-cases for reuse of a seed sequence to construct identical bit generators
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// may be helpful (eg. replaying a simulation whose state is derived from bit
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// generator values).
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//
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// If bitgen == nullptr, then behavior is undefined.
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//
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// Example:
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//
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// absl::BitGen my_bitgen;
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// auto seed_seq = absl::CreateSeedSeqFrom(&my_bitgen);
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// absl::BitGen new_engine(seed_seq); // derived from my_bitgen, but not
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// // correlated.
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//
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template <typename URBG>
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SeedSeq CreateSeedSeqFrom(URBG* urbg) {
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SeedSeq::result_type
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seed_material[random_internal::kEntropyBlocksNeeded];
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if (!random_internal::ReadSeedMaterialFromURBG(
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urbg, absl::MakeSpan(seed_material))) {
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random_internal::ThrowSeedGenException();
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}
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return SeedSeq(std::begin(seed_material), std::end(seed_material));
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}
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// -----------------------------------------------------------------------------
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// absl::MakeSeedSeq()
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// -----------------------------------------------------------------------------
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//
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// Constructs an `absl::SeedSeq` salting the generated values using
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// implementation-defined entropy. The returned sequence can be used to create
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// equivalent bit generators correlated using this sequence.
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//
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// Example:
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//
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// auto my_seed_seq = absl::MakeSeedSeq();
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// std::mt19937 rng1(my_seed_seq);
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// std::mt19937 rng2(my_seed_seq);
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// EXPECT_EQ(rng1(), rng2());
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//
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SeedSeq MakeSeedSeq();
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_SEED_SEQUENCES_H_
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