raw_hash_set.cc
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1 // Copyright 2018 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 
16 
17 #include <atomic>
18 #include <cstddef>
19 
20 #include "absl/base/config.h"
21 
22 namespace absl {
23 namespace container_internal {
24 
25 constexpr size_t Group::kWidth;
26 
27 // Returns "random" seed.
28 inline size_t RandomSeed() {
29 #if ABSL_HAVE_THREAD_LOCAL
30  static thread_local size_t counter = 0;
31  size_t value = ++counter;
32 #else // ABSL_HAVE_THREAD_LOCAL
33  static std::atomic<size_t> counter(0);
34  size_t value = counter.fetch_add(1, std::memory_order_relaxed);
35 #endif // ABSL_HAVE_THREAD_LOCAL
36  return value ^ static_cast<size_t>(reinterpret_cast<uintptr_t>(&counter));
37 }
38 
39 bool ShouldInsertBackwards(size_t hash, ctrl_t* ctrl) {
40  // To avoid problems with weak hashes and single bit tests, we use % 13.
41  // TODO(kfm,sbenza): revisit after we do unconditional mixing
42  return (H1(hash, ctrl) ^ RandomSeed()) % 13 > 6;
43 }
44 
45 } // namespace container_internal
46 } // namespace absl
int * counter
Definition: algorithm.h:29
size_t H1(size_t hash, const ctrl_t *ctrl)
Definition: raw_hash_set.h:304
bool ShouldInsertBackwards(size_t hash, ctrl_t *ctrl)
Definition: raw_hash_set.cc:39
size_t value
hash_default_hash< typename T::first_type > hash


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autogenerated on Tue Jun 18 2019 19:44:37