79 lines
2.4 KiB
C++
79 lines
2.4 KiB
C++
// https://github.com/KoneLinx/small_ECS/blob/master/FastHash.h
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// but slightly modified to abandon ranges
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// Copyright(C) 2021 Kobe Vrijsen <kobevrijsen@posteo.be>
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//
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// A simple ECS example
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//
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// This file is free software and distributed under the terms of the European Union
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// Public Lincense as published by the European Commision; either version 1.2 of the
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// License, or , at your option, any later version.
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/* The MIT License
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Copyright (C) 2012 Zilong Tan (eric.zltan@gmail.com)
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Permission is hereby granted, free of charge, to any person
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obtaining a copy of this software and associated documentation
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files (the "Software"), to deal in the Software without
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restriction, including without limitation the rights to use, copy,
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modify, merge, publish, distribute, sublicense, and/or sell copies
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of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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*/
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// Source: fast-hash https://github.com/ztanml/fast-hash (26 Nov 2021)
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// Changes: General uplift and providing a general constant hash for ranges
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#include <cstdint>
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#pragma once
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// Compression function for Merkle-Damgard construction.
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// This function is generated using the framework provided.
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//#define mix(h) ({
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// (h) ^= (h) >> 23;
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// (h) *= 0x2127599bf4325c37ULL;
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// (h) ^= (h) >> 47; })
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constexpr uint64_t FastHash(const char* str, std::size_t size, uint64_t seed/*, uint64_t back = {}*/)
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{
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auto const mix = [](uint64_t h)
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{
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h ^= h >> 23;
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h *= 0x2127599bf4325c37ULL;
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h ^= h >> 47;
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return h;
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};
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const uint64_t m = 0x880355f21e6d1965ULL;
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uint64_t h = seed ^ (size * m);
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for (std::size_t i = 0; i < size; i++)
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{
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h ^= mix(static_cast<uint64_t>(str[i]));
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h *= m;
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}
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//if (back != uint64_t())
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//{
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// h ^= mix(back);
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// h *= m;
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//}
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return mix(h);
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}
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