qbit/go
1
0
Fork 0
mirror of https://github.com/golang/go synced 2024-11-26 21:01:31 -07:00
Code Releases Activity

runtime: a better fallback hash

Browse Source 
For arm and powerpc, as well as x86 without aes instructions.
Contains a mixture of ideas from cityhash and xxhash.

Compared to our old fallback on ARM, it's ~no slower on
small objects and up to ~50% faster on large objects.  More
importantly, it is a much better hash function and thus has
less chance of bad behavior.

Fixes #8737

benchmark                         old ns/op     new ns/op     delta
BenchmarkHash5                    173           181           +4.62%
BenchmarkHash16                   252           212           -15.87%
BenchmarkHash64                   575           419           -27.13%
BenchmarkHash1024                 7173          3995          -44.31%
BenchmarkHash65536                516940        313173        -39.42%
BenchmarkHashStringSpeed          300           279           -7.00%
BenchmarkHashBytesSpeed           478           424           -11.30%
BenchmarkHashInt32Speed           217           207           -4.61%
BenchmarkHashInt64Speed           262           231           -11.83%
BenchmarkHashStringArraySpeed     609           631           +3.61%

Change-Id: I0a9335028f32b10ad484966e3019987973afd3eb
Reviewed-on: https://go-review.googlesource.com/1360
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Keith Randall 2014-12-10 17:02:58 -08:00
parent fbc56cf050
commit cda0ea1c0e
7 changed files with 229 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
src/runtime/alg.go
View File

@ -72,8 +72,6 @@ var algarray = [alg_max]typeAlg{
alg_CPLX128: {c128hash, c128equal},
}
const nacl = GOOS == "nacl"
var useAeshash bool
// in asm_*.s
@ -82,22 +80,9 @@ func aeshash32(p unsafe.Pointer, s, h uintptr) uintptr
func aeshash64(p unsafe.Pointer, s, h uintptr) uintptr
func aeshashstr(p unsafe.Pointer, s, h uintptr) uintptr
func memhash(p unsafe.Pointer, s, h uintptr) uintptr {
if !nacl && useAeshash {
return aeshash(p, s, h)
}
h ^= c0
for s > 0 {
h = (h ^ uintptr(*(*byte)(p))) * c1
p = add(p, 1)
s--
}
return h
}
func strhash(a unsafe.Pointer, s, h uintptr) uintptr {
return memhash((*stringStruct)(a).str, uintptr(len(*(*string)(a))), h)
x := (*stringStruct)(a)
return memhash(x.str, uintptr(x.len), h)
}
// NOTE: Because NaN != NaN, a map can contain any
@ -267,10 +252,6 @@ func ifaceeq(p, q interface {
}
// Testing adapters for hash quality tests (see hash_test.go)
func haveGoodHash() bool {
return useAeshash
}
func stringHash(s string, seed uintptr) uintptr {
return algarray[alg_STRING].hash(noescape(unsafe.Pointer(&s)), unsafe.Sizeof(s), seed)
}
@ -315,7 +296,7 @@ const hashRandomBytes = ptrSize / 4 * 64
var aeskeysched [hashRandomBytes]byte
func init() {
if theGoos == "nacl" {
if GOOS == "nacl" {
return
}

1
src/runtime/export_test.go
View File

@ -103,7 +103,6 @@ func RunSchedLocalQueueStealTest() {
systemstack(testSchedLocalQueueSteal)
}
var HaveGoodHash = haveGoodHash
var StringHash = stringHash
var BytesHash = bytesHash
var Int32Hash = int32Hash

93
src/runtime/hash32.go Normal file
View File

@ -0,0 +1,93 @@
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Hashing algorithm inspired by
// xxhash: https://code.google.com/p/xxhash/
// cityhash: https://code.google.com/p/cityhash/
// +build 386 arm
package runtime
import "unsafe"
const (
// Constants for multiplication: four random odd 32-bit numbers.
m1 = 3168982561
m2 = 3339683297
m3 = 832293441
m4 = 2336365089
)
func memhash(p unsafe.Pointer, s, seed uintptr) uintptr {
if GOARCH == "386" && GOOS != "nacl" && useAeshash {
return aeshash(p, s, seed)
}
h := uint32(seed + s)
tail:
switch {
case s == 0:
case s < 4:
w := uint32(*(*byte)(p))
w += uint32(*(*byte)(add(p, s>>1))) << 8
w += uint32(*(*byte)(add(p, s-1))) << 16
h ^= w * m1
case s == 4:
h ^= readUnaligned32(p) * m1
case s <= 8:
h ^= readUnaligned32(p) * m1
h = rotl_15(h) * m2
h = rotl_11(h)
h ^= readUnaligned32(add(p, s-4)) * m1
case s <= 16:
h ^= readUnaligned32(p) * m1
h = rotl_15(h) * m2
h = rotl_11(h)
h ^= readUnaligned32(add(p, 4)) * m1
h = rotl_15(h) * m2
h = rotl_11(h)
h ^= readUnaligned32(add(p, s-8)) * m1
h = rotl_15(h) * m2
h = rotl_11(h)
h ^= readUnaligned32(add(p, s-4)) * m1
default:
v1 := h
v2 := h + m1
v3 := h + m2
v4 := h + m3
for s >= 16 {
v1 ^= readUnaligned32(p) * m1
v1 = rotl_15(v1) * m2
p = add(p, 4)
v2 ^= readUnaligned32(p) * m1
v2 = rotl_15(v2) * m2
p = add(p, 4)
v3 ^= readUnaligned32(p) * m1
v3 = rotl_15(v3) * m2
p = add(p, 4)
v4 ^= readUnaligned32(p) * m1
v4 = rotl_15(v4) * m2
p = add(p, 4)
s -= 16
}
h = rotl_11(v1)*m1 + rotl_11(v2)*m2 + rotl_11(v3)*m3 + rotl_11(v4)*m4
goto tail
}
h ^= h >> 17
h *= m3
h ^= h >> 13
h *= m4
h ^= h >> 16
return uintptr(h)
}
// Note: in order to get the compiler to issue rotl instructions, we
// need to constant fold the shift amount by hand.
// TODO: convince the compiler to issue rotl instructions after inlining.
func rotl_15(x uint32) uint32 {
return (x << 15) | (x >> (32 - 15))
}
func rotl_11(x uint32) uint32 {
return (x << 11) | (x >> (32 - 11))
}

96
src/runtime/hash64.go Normal file
View File

@ -0,0 +1,96 @@
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Hashing algorithm inspired by
// xxhash: https://code.google.com/p/xxhash/
// cityhash: https://code.google.com/p/cityhash/
// +build amd64 amd64p32 ppc64 ppc64le
package runtime
import "unsafe"
const (
// Constants for multiplication: four random odd 64-bit numbers.
m1 = 16877499708836156737
m2 = 2820277070424839065
m3 = 9497967016996688599
m4 = 15839092249703872147
)
func memhash(p unsafe.Pointer, s, seed uintptr) uintptr {
if GOARCH == "amd64" && GOOS != "nacl" && useAeshash {
return aeshash(p, s, seed)
}
h := uint64(seed + s)
tail:
switch {
case s == 0:
case s < 4:
w := uint64(*(*byte)(p))
w += uint64(*(*byte)(add(p, s>>1))) << 8
w += uint64(*(*byte)(add(p, s-1))) << 16
h ^= w * m1
case s <= 8:
w := uint64(readUnaligned32(p))
w += uint64(readUnaligned32(add(p, s-4))) << 32
h ^= w * m1
case s <= 16:
h ^= readUnaligned64(p) * m1
h = rotl_31(h) * m2
h = rotl_27(h)
h ^= readUnaligned64(add(p, s-8)) * m1
case s <= 32:
h ^= readUnaligned64(p) * m1
h = rotl_31(h) * m2
h = rotl_27(h)
h ^= readUnaligned64(add(p, 8)) * m1
h = rotl_31(h) * m2
h = rotl_27(h)
h ^= readUnaligned64(add(p, s-16)) * m1
h = rotl_31(h) * m2
h = rotl_27(h)
h ^= readUnaligned64(add(p, s-8)) * m1
default:
v1 := h
v2 := h + m1
v3 := h + m2
v4 := h + m3
for s >= 32 {
v1 ^= readUnaligned64(p) * m1
v1 = rotl_31(v1) * m2
p = add(p, 8)
v2 ^= readUnaligned64(p) * m1
v2 = rotl_31(v2) * m2
p = add(p, 8)
v3 ^= readUnaligned64(p) * m1
v3 = rotl_31(v3) * m2
p = add(p, 8)
v4 ^= readUnaligned64(p) * m1
v4 = rotl_31(v4) * m2
p = add(p, 8)
s -= 32
}
h = rotl_27(v1)*m1 + rotl_27(v2)*m2 + rotl_27(v3)*m3 + rotl_27(v4)*m4
goto tail
}
h ^= h >> 33
h *= m2
h ^= h >> 29
h *= m3
h ^= h >> 32
return uintptr(h)
}
// Note: in order to get the compiler to issue rotl instructions, we
// need to constant fold the shift amount by hand.
// TODO: convince the compiler to issue rotl instructions after inlining.
func rotl_31(x uint64) uint64 {
return (x << 31) | (x >> (64 - 31))
}
func rotl_27(x uint64) uint64 {
return (x << 27) | (x >> (64 - 27))
}

9
src/runtime/hash_test.go
View File

@ -171,9 +171,6 @@ func TestSmhasherCyclic(t *testing.T) {
if testing.Short() {
t.Skip("Skipping in short mode")
}
if !HaveGoodHash() {
t.Skip("fallback hash not good enough for this test")
}
r := rand.New(rand.NewSource(1234))
const REPEAT = 8
const N = 1000000
@ -235,9 +232,6 @@ func TestSmhasherPermutation(t *testing.T) {
if testing.Short() {
t.Skip("Skipping in short mode")
}
if !HaveGoodHash() {
t.Skip("fallback hash not good enough for this test")
}
permutation(t, []uint32{0, 1, 2, 3, 4, 5, 6, 7}, 8)
permutation(t, []uint32{0, 1 << 29, 2 << 29, 3 << 29, 4 << 29, 5 << 29, 6 << 29, 7 << 29}, 8)
permutation(t, []uint32{0, 1}, 20)
@ -404,9 +398,6 @@ func (k *IfaceKey) name() string {
// Flipping a single bit of a key should flip each output bit with 50% probability.
func TestSmhasherAvalanche(t *testing.T) {
if !HaveGoodHash() {
t.Skip("fallback hash not good enough for this test")
}
if testing.Short() {
t.Skip("Skipping in short mode")
}

17
src/runtime/unaligned1.go Normal file
View File

@ -0,0 +1,17 @@
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build 386 amd64 amd64p32
package runtime
import "unsafe"
func readUnaligned32(p unsafe.Pointer) uint32 {
return *(*uint32)(p)
}
func readUnaligned64(p unsafe.Pointer) uint64 {
return *(*uint64)(p)
}

20
src/runtime/unaligned2.go Normal file
View File

@ -0,0 +1,20 @@
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build arm ppc64 ppc64le
package runtime
import "unsafe"
// Note: These routines perform the read with an unspecified endianness.
func readUnaligned32(p unsafe.Pointer) uint32 {
q := (*[4]byte)(p)
return uint32(q[0]) + uint32(q[1])<<8 + uint32(q[2])<<16 + uint32(q[3])<<24
}
func readUnaligned64(p unsafe.Pointer) uint64 {
q := (*[8]byte)(p)
return uint64(q[0]) + uint64(q[1])<<8 + uint64(q[2])<<16 + uint64(q[3])<<24 + uint64(q[4])<<32 + uint64(q[5])<<40 + uint64(q[6])<<48 + uint64(q[7])<<56
}