43 lines
1.2 KiB
Go
43 lines
1.2 KiB
Go
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//
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// hash.go
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// Copyright (C) 2023 tiglog <me@tiglog.com>
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//
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// Distributed under terms of the MIT license.
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//
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package gcache
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// IHash is responsible for generating unsigned, 64-bit hash of provided string. IHash should minimize collisions
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// (generating same hash for different strings) and while performance is also important fast functions are preferable (i.e.
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// you can use FarmHash family).
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type IHash interface {
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Sum64(string) uint64
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}
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// newDefaultHash returns a new 64-bit FNV-1a IHash which makes no memory allocations.
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// Its Sum64 method will lay the value out in big-endian byte order.
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// See https://en.wikipedia.org/wiki/Fowler–Noll–Vo_hash_function
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func newDefaultHash() IHash {
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return fnv64a{}
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}
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type fnv64a struct{}
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const (
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// offset64 FNVa offset basis. See https://en.wikipedia.org/wiki/Fowler–Noll–Vo_hash_function#FNV-1a_hash
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offset64 = 14695981039346656037
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// prime64 FNVa prime value. See https://en.wikipedia.org/wiki/Fowler–Noll–Vo_hash_function#FNV-1a_hash
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prime64 = 1099511628211
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)
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// Sum64 gets the string and returns its uint64 hash value.
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func (f fnv64a) Sum64(key string) uint64 {
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var hash uint64 = offset64
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for i := 0; i < len(key); i++ {
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hash ^= uint64(key[i])
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hash *= prime64
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}
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return hash
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}
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