| // Copyright 2018 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. |
| |
| #include "absl/container/internal/raw_hash_set.h" |
| |
| #include <atomic> |
| #include <cstddef> |
| |
| #include "absl/base/config.h" |
| |
| namespace absl { |
| ABSL_NAMESPACE_BEGIN |
| namespace container_internal { |
| |
| // A single block of empty control bytes for tables without any slots allocated. |
| // This enables removing a branch in the hot path of find(). |
| alignas(16) ABSL_CONST_INIT ABSL_DLL const ctrl_t kEmptyGroup[16] = { |
| ctrl_t::kSentinel, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, |
| ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, |
| ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, |
| ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty}; |
| |
| constexpr size_t Group::kWidth; |
| |
| // Returns "random" seed. |
| inline size_t RandomSeed() { |
| #ifdef ABSL_HAVE_THREAD_LOCAL |
| static thread_local size_t counter = 0; |
| size_t value = ++counter; |
| #else // ABSL_HAVE_THREAD_LOCAL |
| static std::atomic<size_t> counter(0); |
| size_t value = counter.fetch_add(1, std::memory_order_relaxed); |
| #endif // ABSL_HAVE_THREAD_LOCAL |
| return value ^ static_cast<size_t>(reinterpret_cast<uintptr_t>(&counter)); |
| } |
| |
| bool ShouldInsertBackwards(size_t hash, const ctrl_t* ctrl) { |
| // To avoid problems with weak hashes and single bit tests, we use % 13. |
| // TODO(kfm,sbenza): revisit after we do unconditional mixing |
| return (H1(hash, ctrl) ^ RandomSeed()) % 13 > 6; |
| } |
| |
| void ConvertDeletedToEmptyAndFullToDeleted(ctrl_t* ctrl, size_t capacity) { |
| assert(ctrl[capacity] == ctrl_t::kSentinel); |
| assert(IsValidCapacity(capacity)); |
| for (ctrl_t* pos = ctrl; pos < ctrl + capacity; pos += Group::kWidth) { |
| Group{pos}.ConvertSpecialToEmptyAndFullToDeleted(pos); |
| } |
| // Copy the cloned ctrl bytes. |
| std::memcpy(ctrl + capacity + 1, ctrl, NumClonedBytes()); |
| ctrl[capacity] = ctrl_t::kSentinel; |
| } |
| // Extern template instantiotion for inline function. |
| template FindInfo find_first_non_full(const ctrl_t*, size_t, size_t); |
| |
| } // namespace container_internal |
| ABSL_NAMESPACE_END |
| } // namespace absl |