94 lines
2.4 KiB
C++
94 lines
2.4 KiB
C++
/*
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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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* http://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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* Copyright 2015 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef __UTIL_HASH_MURMUR_MURMUR2_HPP
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#define __UTIL_HASH_MURMUR_MURMUR2_HPP
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#include "../../view.hpp"
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#include <cstddef>
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#include <cstdint>
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// Austin Appleby's MumurHash2, and MurmurHash64A. The exhaustive list of
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// variants is deliberately not provided. You can damn well align your data or
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// fix the algorithm.
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namespace util::hash {
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namespace detail::murmur2 {
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template <typename T> struct constants;
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template <>
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struct constants<uint32_t> {
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static const uint32_t m = 0x5bd1e995;
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static const int32_t r = 24;
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};
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template <>
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struct constants<uint64_t> {
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static const uint64_t m = 0xc6a4a7935bd1e995;
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static const int64_t r = 47;
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};
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}
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template <typename DigestT>
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class murmur2 {
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public:
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using digest_t = DigestT;
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using seed_t = DigestT;
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murmur2 (seed_t _seed):
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m_seed (_seed)
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{ ; }
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static constexpr uint32_t mix (uint32_t h, uint32_t k)
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{
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constexpr uint32_t m = detail::murmur2::constants<uint32_t>::m;
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constexpr uint32_t r = detail::murmur2::constants<uint32_t>::r;
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k *= m;
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k ^= k >> r;
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k *= m;
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h *= m;
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h ^= k;
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return h;
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}
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static constexpr uint64_t mix (uint64_t h, uint64_t k)
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{
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constexpr uint64_t m = detail::murmur2::constants<uint64_t>::m;
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constexpr uint64_t r = detail::murmur2::constants<uint64_t>::r;
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k *= m;
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k ^= k >> r;
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k *= m;
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h ^= k;
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h *= m;
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return h;
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}
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digest_t operator() (util::view<const uint8_t*> data) const noexcept;
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private:
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seed_t m_seed;
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};
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}
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#endif
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