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https://github.com/LadybirdBrowser/ladybird
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1745926fc6
Rework our hash functions a bit for significant better performance: * Rename int_hash to u32_hash to mirror u64_hash. * Make pair_int_hash call u64_hash instead of multiple u32_hash()es. * Implement MurmurHash3's fmix32 and fmix64 for u32_hash and u64_hash. On my machine, this speeds up u32_hash by 20%, u64_hash by ~290%, and pair_int_hash by ~260%. We lose the property that an input of 0 results in something that is not 0. I've experimented with an offset to both hash functions, but it resulted in a measurable performance degradation for u64_hash. If there's a good use case for 0 not to result in 0, we can always add in that offset as a countermeasure in the future.
50 lines
975 B
C++
50 lines
975 B
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <andreas@ladybird.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Types.h>
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// MurmurHash3 32-bit finalizer (fmix32).
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constexpr unsigned u32_hash(u32 key)
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{
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key ^= key >> 16;
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key *= 0x85ebca6bU;
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key ^= key >> 13;
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key *= 0xc2b2ae35U;
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key ^= key >> 16;
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return key;
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}
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// MurmurHash3 64-bit finalizer (fmix64).
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constexpr unsigned u64_hash(u64 key)
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{
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key ^= key >> 33;
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key *= 0xff51afd7ed558ccdULL;
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key ^= key >> 33;
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key *= 0xc4ceb9fe1a85ec53ULL;
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key ^= key >> 33;
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return static_cast<unsigned>(key);
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}
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constexpr unsigned pair_int_hash(u32 key1, u32 key2)
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{
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return u64_hash((static_cast<u64>(key1) << 32) | key2);
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}
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constexpr unsigned ptr_hash(FlatPtr ptr)
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{
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if constexpr (sizeof(ptr) == 8)
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return u64_hash(ptr);
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else
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return u32_hash(ptr);
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}
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inline unsigned ptr_hash(void const* ptr)
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{
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return ptr_hash(FlatPtr(ptr));
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}
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