mirror of
https://github.com/golang/go
synced 2024-11-19 14:54:43 -07:00
94 lines
2.1 KiB
Go
94 lines
2.1 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 386 arm
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package runtime
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import "unsafe"
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const (
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// Constants for multiplication: four random odd 32-bit numbers.
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m1 = 3168982561
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m2 = 3339683297
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m3 = 832293441
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m4 = 2336365089
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)
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func memhash(p unsafe.Pointer, s, seed uintptr) uintptr {
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if GOARCH == "386" && GOOS != "nacl" && useAeshash {
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return aeshash(p, s, seed)
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}
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h := uint32(seed + s)
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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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w := uint32(*(*byte)(p))
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w += uint32(*(*byte)(add(p, s>>1))) << 8
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w += uint32(*(*byte)(add(p, s-1))) << 16
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h ^= w * m1
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case s == 4:
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h ^= readUnaligned32(p) * m1
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case s <= 8:
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h ^= readUnaligned32(p) * m1
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h = rotl_15(h) * m2
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h = rotl_11(h)
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h ^= readUnaligned32(add(p, s-4)) * m1
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case s <= 16:
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h ^= readUnaligned32(p) * m1
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h = rotl_15(h) * m2
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h = rotl_11(h)
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h ^= readUnaligned32(add(p, 4)) * m1
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h = rotl_15(h) * m2
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h = rotl_11(h)
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h ^= readUnaligned32(add(p, s-8)) * m1
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h = rotl_15(h) * m2
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h = rotl_11(h)
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h ^= readUnaligned32(add(p, s-4)) * m1
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default:
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v1 := h
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v2 := h + m1
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v3 := h + m2
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v4 := h + m3
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for s >= 16 {
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v1 ^= readUnaligned32(p) * m1
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v1 = rotl_15(v1) * m2
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p = add(p, 4)
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v2 ^= readUnaligned32(p) * m1
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v2 = rotl_15(v2) * m2
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p = add(p, 4)
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v3 ^= readUnaligned32(p) * m1
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v3 = rotl_15(v3) * m2
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p = add(p, 4)
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v4 ^= readUnaligned32(p) * m1
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v4 = rotl_15(v4) * m2
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p = add(p, 4)
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s -= 16
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}
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h = rotl_11(v1)*m1 + rotl_11(v2)*m2 + rotl_11(v3)*m3 + rotl_11(v4)*m4
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goto tail
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}
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h ^= h >> 17
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h *= m3
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h ^= h >> 13
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h *= m4
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h ^= h >> 16
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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_15(x uint32) uint32 {
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return (x << 15) | (x >> (32 - 15))
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}
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func rotl_11(x uint32) uint32 {
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return (x << 11) | (x >> (32 - 11))
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}
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