81 lines
2.0 KiB
C++
81 lines
2.0 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2015 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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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 cruft::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() (cruft::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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} |