mirror of
https://github.com/tinygo-org/tinygo.git
synced 2026-08-04 19:17:47 +00:00
Damian Gryski
72 lines
1.8 KiB
Go
72 lines
1.8 KiB
Go
//go:build runtime_memhash_leveldb || (wasip1 && !runtime_memhash_fnv && !runtime_memhash_tsip)
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// This is the default for WASI, but can also be used on other targets with the
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// right build tag.
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// This is the hash function from Google's leveldb key-value storage system. It
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// processes 4 bytes at a time making it faster than the FNV hash for buffer
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// lengths > 16 bytes.
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// https://github.com/google/leveldb
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// https://en.wikipedia.org/wiki/LevelDB
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package runtime
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import (
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"unsafe"
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)
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// leveldb hash
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func hash32(ptr unsafe.Pointer, n, seed uintptr) uint32 {
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const (
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lseed = 0xbc9f1d34
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m = 0xc6a4a793
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)
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b := unsafe.Slice((*byte)(ptr), n)
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h := uint32(lseed^seed) ^ uint32(uint(len(b))*uint(m))
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for ; len(b) >= 4; b = b[4:] {
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h += uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
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h *= m
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h ^= h >> 16
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}
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switch len(b) {
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case 3:
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h += uint32(b[2]) << 16
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fallthrough
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case 2:
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h += uint32(b[1]) << 8
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fallthrough
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case 1:
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h += uint32(b[0])
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h *= m
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h ^= h >> 24
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}
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return h
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}
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// hash64finalizer is a 64-bit integer mixing function from
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// https://web.archive.org/web/20120720045250/http://www.cris.com/~Ttwang/tech/inthash.htm
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func hash64finalizer(key uint64) uint64 {
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key = ^key + (key << 21) // key = (key << 21) - key - 1;
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key = key ^ (key >> 24)
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key = (key + (key << 3)) + (key << 8) // key * 265
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key = key ^ (key >> 14)
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key = (key + (key << 2)) + (key << 4) // key * 21
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key = key ^ (key >> 28)
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key = key + (key << 31)
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return key
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}
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// hash64 turns hash32 into a 64-bit hash, by use hash64finalizer to
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// mix the result of hash32 function combined with an xorshifted version of
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// the seed.
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func hash64(ptr unsafe.Pointer, n, seed uintptr) uint64 {
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h32 := hash32(ptr, n, seed)
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return hash64finalizer((uint64(h32^xorshift32(uint32(seed))) << 32) | uint64(h32))
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}
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