mirror of
https://github.com/SerenityOS/serenity
synced 2024-07-22 10:36:24 +00:00
55a7738837
The previous implementation had some pretty short cycles and two fixed points (1711463637 and 2389024350). If two keys hashed to one of these values insertions and lookups would loop forever. This version is based on a standard xorshift PRNG with period 2**32-1. The all-zero state is usually forbidden, so we insert it into the cycle at an arbitrary location.
60 lines
1.1 KiB
C++
60 lines
1.1 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.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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constexpr unsigned int_hash(u32 key)
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{
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key += ~(key << 15);
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key ^= (key >> 10);
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key += (key << 3);
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key ^= (key >> 6);
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key += ~(key << 11);
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key ^= (key >> 16);
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return key;
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}
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constexpr unsigned double_hash(u32 key)
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{
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const unsigned magic = 0xBA5EDB01;
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if (key == magic)
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return 0u;
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if (key == 0u)
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key = magic;
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key ^= key << 13;
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key ^= key >> 17;
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key ^= key << 5;
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return 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 int_hash((int_hash(key1) * 209) ^ (int_hash(key2 * 413)));
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}
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constexpr unsigned u64_hash(u64 key)
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{
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u32 first = key & 0xFFFFFFFF;
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u32 last = key >> 32;
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return pair_int_hash(first, last);
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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 int_hash(ptr);
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}
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inline unsigned ptr_hash(const void* ptr)
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{
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return ptr_hash(FlatPtr(ptr));
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}
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