mirror of
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95 lines
2.4 KiB
Go
95 lines
2.4 KiB
Go
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Hashing algorithm inspired by
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// xxhash: https://code.google.com/p/xxhash/
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// cityhash: https://code.google.com/p/cityhash/
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// +build amd64 amd64p32 arm64 mips64 mips64le ppc64 ppc64le s390x alpha arm64be ia64 mipso64 mipsn64 mips64p32 mips64p32le sparc64
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package runtime
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import "unsafe"
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// For gccgo, use go:linkname to rename compiler-called functions to
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// themselves, so that the compiler will export them.
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//
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//go:linkname memhash runtime.memhash
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const (
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// Constants for multiplication: four random odd 64-bit numbers.
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m1 = 16877499708836156737
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m2 = 2820277070424839065
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m3 = 9497967016996688599
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m4 = 15839092249703872147
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)
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func memhash(p unsafe.Pointer, seed, s uintptr) uintptr {
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if GOARCH == "amd64" && GOOS != "nacl" && useAeshash {
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return aeshash(p, seed, s)
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}
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h := uint64(seed + s*hashkey[0])
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tail:
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switch {
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case s == 0:
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case s < 4:
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h ^= uint64(*(*byte)(p))
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h ^= uint64(*(*byte)(add(p, s>>1))) << 8
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h ^= uint64(*(*byte)(add(p, s-1))) << 16
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h = rotl_31(h*m1) * m2
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case s <= 8:
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h ^= uint64(readUnaligned32(p))
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h ^= uint64(readUnaligned32(add(p, s-4))) << 32
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h = rotl_31(h*m1) * m2
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case s <= 16:
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h ^= readUnaligned64(p)
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h = rotl_31(h*m1) * m2
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h ^= readUnaligned64(add(p, s-8))
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h = rotl_31(h*m1) * m2
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case s <= 32:
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h ^= readUnaligned64(p)
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h = rotl_31(h*m1) * m2
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h ^= readUnaligned64(add(p, 8))
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h = rotl_31(h*m1) * m2
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h ^= readUnaligned64(add(p, s-16))
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h = rotl_31(h*m1) * m2
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h ^= readUnaligned64(add(p, s-8))
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h = rotl_31(h*m1) * m2
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default:
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v1 := h
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v2 := uint64(seed * hashkey[1])
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v3 := uint64(seed * hashkey[2])
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v4 := uint64(seed * hashkey[3])
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for s >= 32 {
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v1 ^= readUnaligned64(p)
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v1 = rotl_31(v1*m1) * m2
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p = add(p, 8)
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v2 ^= readUnaligned64(p)
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v2 = rotl_31(v2*m2) * m3
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p = add(p, 8)
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v3 ^= readUnaligned64(p)
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v3 = rotl_31(v3*m3) * m4
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p = add(p, 8)
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v4 ^= readUnaligned64(p)
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v4 = rotl_31(v4*m4) * m1
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p = add(p, 8)
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s -= 32
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}
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h = v1 ^ v2 ^ v3 ^ v4
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goto tail
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}
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h ^= h >> 29
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h *= m3
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h ^= h >> 32
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return uintptr(h)
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}
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// Note: in order to get the compiler to issue rotl instructions, we
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// need to constant fold the shift amount by hand.
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// TODO: convince the compiler to issue rotl instructions after inlining.
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func rotl_31(x uint64) uint64 {
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return (x << 31) | (x >> (64 - 31))
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}
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