1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
|
// Copyright 2011 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.
// AMD64-specific hardware-assisted CRC32 algorithms. See crc32.go for a
// description of the interface that each architecture-specific file
// implements.
package crc32
import (
"internal/cpu"
"unsafe"
)
// This file contains the code to call the SSE 4.2 version of the Castagnoli
// and IEEE CRC.
// castagnoliSSE42 is defined in crc32_amd64.s and uses the SSE 4.2 CRC32
// instruction.
//go:noescape
func castagnoliSSE42(crc uint32, p []byte) uint32
// castagnoliSSE42Triple is defined in crc32_amd64.s and uses the SSE 4.2 CRC32
// instruction.
//go:noescape
func castagnoliSSE42Triple(
crcA, crcB, crcC uint32,
a, b, c []byte,
rounds uint32,
) (retA uint32, retB uint32, retC uint32)
// ieeeCLMUL is defined in crc_amd64.s and uses the PCLMULQDQ
// instruction as well as SSE 4.1.
//go:noescape
func ieeeCLMUL(crc uint32, p []byte) uint32
const castagnoliK1 = 168
const castagnoliK2 = 1344
type sse42Table [4]Table
var castagnoliSSE42TableK1 *sse42Table
var castagnoliSSE42TableK2 *sse42Table
func archAvailableCastagnoli() bool {
return cpu.X86.HasSSE42
}
func archInitCastagnoli() {
if !cpu.X86.HasSSE42 {
panic("arch-specific Castagnoli not available")
}
castagnoliSSE42TableK1 = new(sse42Table)
castagnoliSSE42TableK2 = new(sse42Table)
// See description in updateCastagnoli.
// t[0][i] = CRC(i000, O)
// t[1][i] = CRC(0i00, O)
// t[2][i] = CRC(00i0, O)
// t[3][i] = CRC(000i, O)
// where O is a sequence of K zeros.
var tmp [castagnoliK2]byte
for b := 0; b < 4; b++ {
for i := 0; i < 256; i++ {
val := uint32(i) << uint32(b*8)
castagnoliSSE42TableK1[b][i] = castagnoliSSE42(val, tmp[:castagnoliK1])
castagnoliSSE42TableK2[b][i] = castagnoliSSE42(val, tmp[:])
}
}
}
// castagnoliShift computes the CRC32-C of K1 or K2 zeroes (depending on the
// table given) with the given initial crc value. This corresponds to
// CRC(crc, O) in the description in updateCastagnoli.
func castagnoliShift(table *sse42Table, crc uint32) uint32 {
return table[3][crc>>24] ^
table[2][(crc>>16)&0xFF] ^
table[1][(crc>>8)&0xFF] ^
table[0][crc&0xFF]
}
func archUpdateCastagnoli(crc uint32, p []byte) uint32 {
if !cpu.X86.HasSSE42 {
panic("not available")
}
// This method is inspired from the algorithm in Intel's white paper:
// "Fast CRC Computation for iSCSI Polynomial Using CRC32 Instruction"
// The same strategy of splitting the buffer in three is used but the
// combining calculation is different; the complete derivation is explained
// below.
//
// -- The basic idea --
//
// The CRC32 instruction (available in SSE4.2) can process 8 bytes at a
// time. In recent Intel architectures the instruction takes 3 cycles;
// however the processor can pipeline up to three instructions if they
// don't depend on each other.
//
// Roughly this means that we can process three buffers in about the same
// time we can process one buffer.
//
// The idea is then to split the buffer in three, CRC the three pieces
// separately and then combine the results.
//
// Combining the results requires precomputed tables, so we must choose a
// fixed buffer length to optimize. The longer the length, the faster; but
// only buffers longer than this length will use the optimization. We choose
// two cutoffs and compute tables for both:
// - one around 512: 168*3=504
// - one around 4KB: 1344*3=4032
//
// -- The nitty gritty --
//
// Let CRC(I, X) be the non-inverted CRC32-C of the sequence X (with
// initial non-inverted CRC I). This function has the following properties:
// (a) CRC(I, AB) = CRC(CRC(I, A), B)
// (b) CRC(I, A xor B) = CRC(I, A) xor CRC(0, B)
//
// Say we want to compute CRC(I, ABC) where A, B, C are three sequences of
// K bytes each, where K is a fixed constant. Let O be the sequence of K zero
// bytes.
//
// CRC(I, ABC) = CRC(I, ABO xor C)
// = CRC(I, ABO) xor CRC(0, C)
// = CRC(CRC(I, AB), O) xor CRC(0, C)
// = CRC(CRC(I, AO xor B), O) xor CRC(0, C)
// = CRC(CRC(I, AO) xor CRC(0, B), O) xor CRC(0, C)
// = CRC(CRC(CRC(I, A), O) xor CRC(0, B), O) xor CRC(0, C)
//
// The castagnoliSSE42Triple function can compute CRC(I, A), CRC(0, B),
// and CRC(0, C) efficiently. We just need to find a way to quickly compute
// CRC(uvwx, O) given a 4-byte initial value uvwx. We can precompute these
// values; since we can't have a 32-bit table, we break it up into four
// 8-bit tables:
//
// CRC(uvwx, O) = CRC(u000, O) xor
// CRC(0v00, O) xor
// CRC(00w0, O) xor
// CRC(000x, O)
//
// We can compute tables corresponding to the four terms for all 8-bit
// values.
crc = ^crc
// If a buffer is long enough to use the optimization, process the first few
// bytes to align the buffer to an 8 byte boundary (if necessary).
if len(p) >= castagnoliK1*3 {
delta := int(uintptr(unsafe.Pointer(&p[0])) & 7)
if delta != 0 {
delta = 8 - delta
crc = castagnoliSSE42(crc, p[:delta])
p = p[delta:]
}
}
// Process 3*K2 at a time.
for len(p) >= castagnoliK2*3 {
// Compute CRC(I, A), CRC(0, B), and CRC(0, C).
crcA, crcB, crcC := castagnoliSSE42Triple(
crc, 0, 0,
p, p[castagnoliK2:], p[castagnoliK2*2:],
castagnoliK2/24)
// CRC(I, AB) = CRC(CRC(I, A), O) xor CRC(0, B)
crcAB := castagnoliShift(castagnoliSSE42TableK2, crcA) ^ crcB
// CRC(I, ABC) = CRC(CRC(I, AB), O) xor CRC(0, C)
crc = castagnoliShift(castagnoliSSE42TableK2, crcAB) ^ crcC
p = p[castagnoliK2*3:]
}
// Process 3*K1 at a time.
for len(p) >= castagnoliK1*3 {
// Compute CRC(I, A), CRC(0, B), and CRC(0, C).
crcA, crcB, crcC := castagnoliSSE42Triple(
crc, 0, 0,
p, p[castagnoliK1:], p[castagnoliK1*2:],
castagnoliK1/24)
// CRC(I, AB) = CRC(CRC(I, A), O) xor CRC(0, B)
crcAB := castagnoliShift(castagnoliSSE42TableK1, crcA) ^ crcB
// CRC(I, ABC) = CRC(CRC(I, AB), O) xor CRC(0, C)
crc = castagnoliShift(castagnoliSSE42TableK1, crcAB) ^ crcC
p = p[castagnoliK1*3:]
}
// Use the simple implementation for what's left.
crc = castagnoliSSE42(crc, p)
return ^crc
}
func archAvailableIEEE() bool {
return cpu.X86.HasPCLMULQDQ && cpu.X86.HasSSE41
}
var archIeeeTable8 *slicing8Table
func archInitIEEE() {
if !cpu.X86.HasPCLMULQDQ || !cpu.X86.HasSSE41 {
panic("not available")
}
// We still use slicing-by-8 for small buffers.
archIeeeTable8 = slicingMakeTable(IEEE)
}
func archUpdateIEEE(crc uint32, p []byte) uint32 {
if !cpu.X86.HasPCLMULQDQ || !cpu.X86.HasSSE41 {
panic("not available")
}
if len(p) >= 64 {
left := len(p) & 15
do := len(p) - left
crc = ^ieeeCLMUL(^crc, p[:do])
p = p[do:]
}
if len(p) == 0 {
return crc
}
return slicingUpdate(crc, archIeeeTable8, p)
}
|
