46 lines
1.5 KiB
C++
46 lines
1.5 KiB
C++
// Copyright 2018 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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#include "absl/container/internal/raw_hash_set.h"
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#include <atomic>
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#include <cstddef>
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#include "absl/base/config.h"
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namespace absl {
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namespace container_internal {
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constexpr size_t Group::kWidth;
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// Returns "random" seed.
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inline size_t RandomSeed() {
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#if ABSL_HAVE_THREAD_LOCAL
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static thread_local size_t counter = 0;
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size_t value = ++counter;
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#else // ABSL_HAVE_THREAD_LOCAL
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static std::atomic<size_t> counter(0);
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size_t value = counter.fetch_add(1, std::memory_order_relaxed);
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#endif // ABSL_HAVE_THREAD_LOCAL
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return value ^ static_cast<size_t>(reinterpret_cast<uintptr_t>(&counter));
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}
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bool ShouldInsertBackwards(size_t hash, ctrl_t* ctrl) {
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// To avoid problems with weak hashes and single bit tests, we use % 13.
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// TODO(kfm,sbenza): revisit after we do unconditional mixing
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return (H1(hash, ctrl) ^ RandomSeed()) % 13 > 6;
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}
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} // namespace container_internal
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} // namespace absl
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