mirror of
https://github.com/greg7mdp/parallel-hashmap.git
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greg
84 lines
2.3 KiB
C++
Vendored
84 lines
2.3 KiB
C++
Vendored
#if !defined(phmap_utils_h_guard_)
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#define phmap_utils_h_guard_
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// ---------------------------------------------------------------------------
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// Copyright (c) 2019, Gregory Popovitch - greg7mdp@gmail.com
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//
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// minimal header providing phmap::hash_combine
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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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#if defined(__APPLE__)
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// forward declaration of std::hash does not work on mac. It is not really supposed
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// to work, I know, but it is nice to reduce the amount of headers included.
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#include <functional>
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#else
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#include <cstddef> // for size_t
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namespace std
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{
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template<class Key> struct hash;
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}
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#endif
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namespace phmap
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{
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template <class H, int sz> struct Combiner
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{
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H operator()(H seed, size_t value);
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};
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template <class H> struct Combiner<H, 4>
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{
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H operator()(H seed, size_t value)
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{
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return seed ^ (value + 0x9e3779b9 + (seed << 6) + (seed >> 2));
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}
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};
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template <class H> struct Combiner<H, 8>
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{
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H operator()(H seed, size_t value)
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{
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return seed ^ (value + size_t(0xc6a4a7935bd1e995) + (seed << 6) + (seed >> 2));
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}
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};
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// -----------------------------------------------------------------------------
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template <typename H>
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class HashStateBase {
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public:
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template <typename T, typename... Ts>
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static H combine(H state, const T& value, const Ts&... values);
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static H combine(H state) { return state; }
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};
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template <typename H>
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template <typename T, typename... Ts>
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H HashStateBase<H>::combine(H seed, const T& v, const Ts&... vs)
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{
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return HashStateBase<H>::combine(Combiner<H, sizeof(H)>()(
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seed, std::hash<T>()(v)), vs...);
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}
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using HashState = HashStateBase<size_t>;
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} // namespace phmap
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#endif // phmap_utils_h_guard_
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