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https://github.com/golang/go
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91059de095
Improve the aeshash implementation to make it harder to engineer collisions. 1) Scramble the seed before xoring with the input string. This makes it harder to cancel known portions of the seed (like the size) because it mixes the per-table seed into those other parts. 2) Use table-dependent seeds for all stripes when hashing >16 byte strings. For small strings this change uses 4 aesenc ops instead of 3, so it is somewhat slower. The first two can run in parallel, though, so it isn't 33% slower. benchmark old ns/op new ns/op delta BenchmarkHash64-12 10.2 11.2 +9.80% BenchmarkHash16-12 5.71 6.13 +7.36% BenchmarkHash5-12 6.64 7.01 +5.57% BenchmarkHashBytesSpeed-12 30.3 31.9 +5.28% BenchmarkHash65536-12 2785 2882 +3.48% BenchmarkHash1024-12 53.6 55.4 +3.36% BenchmarkHashStringArraySpeed-12 54.9 56.5 +2.91% BenchmarkHashStringSpeed-12 18.7 19.2 +2.67% BenchmarkHashInt32Speed-12 14.8 15.1 +2.03% BenchmarkHashInt64Speed-12 14.5 14.5 +0.00% Change-Id: I59ea124b5cb92b1c7e8584008257347f9049996c Reviewed-on: https://go-review.googlesource.com/14124 Reviewed-by: jcd . <jcd@golang.org> Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
90 lines
2.1 KiB
Go
90 lines
2.1 KiB
Go
// 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, seed, s uintptr) uintptr {
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if GOARCH == "386" && GOOS != "nacl" && useAeshash {
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return aeshash(p, seed, s)
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}
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h := uint32(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 ^= uint32(*(*byte)(p))
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h ^= uint32(*(*byte)(add(p, s>>1))) << 8
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h ^= uint32(*(*byte)(add(p, s-1))) << 16
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h = rotl_15(h*m1) * m2
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case s == 4:
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h ^= readUnaligned32(p)
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h = rotl_15(h*m1) * m2
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case s <= 8:
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h ^= readUnaligned32(p)
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h = rotl_15(h*m1) * m2
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h ^= readUnaligned32(add(p, s-4))
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h = rotl_15(h*m1) * m2
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case s <= 16:
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h ^= readUnaligned32(p)
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h = rotl_15(h*m1) * m2
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h ^= readUnaligned32(add(p, 4))
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h = rotl_15(h*m1) * m2
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h ^= readUnaligned32(add(p, s-8))
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h = rotl_15(h*m1) * m2
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h ^= readUnaligned32(add(p, s-4))
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h = rotl_15(h*m1) * m2
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default:
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v1 := h
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v2 := uint32(seed * hashkey[1])
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v3 := uint32(seed * hashkey[2])
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v4 := uint32(seed * hashkey[3])
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for s >= 16 {
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v1 ^= readUnaligned32(p)
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v1 = rotl_15(v1*m1) * m2
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p = add(p, 4)
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v2 ^= readUnaligned32(p)
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v2 = rotl_15(v2*m2) * m3
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p = add(p, 4)
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v3 ^= readUnaligned32(p)
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v3 = rotl_15(v3*m3) * m4
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p = add(p, 4)
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v4 ^= readUnaligned32(p)
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v4 = rotl_15(v4*m4) * m1
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p = add(p, 4)
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s -= 16
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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 >> 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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