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
|
/* crc32_braid.c -- compute the CRC-32 of a data stream
* Copyright (C) 1995-2022 Mark Adler
* For conditions of distribution and use, see copyright notice in zlib.h
*
* This interleaved implementation of a CRC makes use of pipelined multiple
* arithmetic-logic units, commonly found in modern CPU cores. It is due to
* Kadatch and Jenkins (2010). See doc/crc-doc.1.0.pdf in this distribution.
*/
#include "zbuild.h"
#include "crc32_braid_p.h"
#include "crc32_braid_tbl.h"
/*
A CRC of a message is computed on N braids of words in the message, where
each word consists of W bytes (4 or 8). If N is 3, for example, then three
running sparse CRCs are calculated respectively on each braid, at these
indices in the array of words: 0, 3, 6, ..., 1, 4, 7, ..., and 2, 5, 8, ...
This is done starting at a word boundary, and continues until as many blocks
of N * W bytes as are available have been processed. The results are combined
into a single CRC at the end. For this code, N must be in the range 1..6 and
W must be 4 or 8. The upper limit on N can be increased if desired by adding
more #if blocks, extending the patterns apparent in the code. In addition,
crc32 tables would need to be regenerated, if the maximum N value is increased.
N and W are chosen empirically by benchmarking the execution time on a given
processor. The choices for N and W below were based on testing on Intel Kaby
Lake i7, AMD Ryzen 7, ARM Cortex-A57, Sparc64-VII, PowerPC POWER9, and MIPS64
Octeon II processors. The Intel, AMD, and ARM processors were all fastest
with N=5, W=8. The Sparc, PowerPC, and MIPS64 were all fastest at N=5, W=4.
They were all tested with either gcc or clang, all using the -O3 optimization
level. Your mileage may vary.
*/
/* ========================================================================= */
#ifdef W
/*
Return the CRC of the W bytes in the word_t data, taking the
least-significant byte of the word as the first byte of data, without any pre
or post conditioning. This is used to combine the CRCs of each braid.
*/
#if BYTE_ORDER == LITTLE_ENDIAN
static uint32_t crc_word(z_word_t data) {
int k;
for (k = 0; k < W; k++)
data = (data >> 8) ^ crc_table[data & 0xff];
return (uint32_t)data;
}
#elif BYTE_ORDER == BIG_ENDIAN
static z_word_t crc_word(z_word_t data) {
int k;
for (k = 0; k < W; k++)
data = (data << 8) ^
crc_big_table[(data >> ((W - 1) << 3)) & 0xff];
return data;
}
#endif /* BYTE_ORDER */
#endif /* W */
/* ========================================================================= */
Z_INTERNAL uint32_t PREFIX(crc32_braid)(uint32_t crc, const uint8_t *buf, size_t len) {
uint32_t c;
/* Pre-condition the CRC */
c = (~crc) & 0xffffffff;
#ifdef W
/* If provided enough bytes, do a braided CRC calculation. */
if (len >= N * W + W - 1) {
size_t blks;
z_word_t const *words;
int k;
/* Compute the CRC up to a z_word_t boundary. */
while (len && ((uintptr_t)buf & (W - 1)) != 0) {
len--;
DO1;
}
/* Compute the CRC on as many N z_word_t blocks as are available. */
blks = len / (N * W);
len -= blks * N * W;
words = (z_word_t const *)buf;
z_word_t crc0, word0, comb;
#if N > 1
z_word_t crc1, word1;
#if N > 2
z_word_t crc2, word2;
#if N > 3
z_word_t crc3, word3;
#if N > 4
z_word_t crc4, word4;
#if N > 5
z_word_t crc5, word5;
#endif
#endif
#endif
#endif
#endif
/* Initialize the CRC for each braid. */
crc0 = ZSWAPWORD(c);
#if N > 1
crc1 = 0;
#if N > 2
crc2 = 0;
#if N > 3
crc3 = 0;
#if N > 4
crc4 = 0;
#if N > 5
crc5 = 0;
#endif
#endif
#endif
#endif
#endif
/* Process the first blks-1 blocks, computing the CRCs on each braid independently. */
while (--blks) {
/* Load the word for each braid into registers. */
word0 = crc0 ^ words[0];
#if N > 1
word1 = crc1 ^ words[1];
#if N > 2
word2 = crc2 ^ words[2];
#if N > 3
word3 = crc3 ^ words[3];
#if N > 4
word4 = crc4 ^ words[4];
#if N > 5
word5 = crc5 ^ words[5];
#endif
#endif
#endif
#endif
#endif
words += N;
/* Compute and update the CRC for each word. The loop should get unrolled. */
crc0 = BRAID_TABLE[0][word0 & 0xff];
#if N > 1
crc1 = BRAID_TABLE[0][word1 & 0xff];
#if N > 2
crc2 = BRAID_TABLE[0][word2 & 0xff];
#if N > 3
crc3 = BRAID_TABLE[0][word3 & 0xff];
#if N > 4
crc4 = BRAID_TABLE[0][word4 & 0xff];
#if N > 5
crc5 = BRAID_TABLE[0][word5 & 0xff];
#endif
#endif
#endif
#endif
#endif
for (k = 1; k < W; k++) {
crc0 ^= BRAID_TABLE[k][(word0 >> (k << 3)) & 0xff];
#if N > 1
crc1 ^= BRAID_TABLE[k][(word1 >> (k << 3)) & 0xff];
#if N > 2
crc2 ^= BRAID_TABLE[k][(word2 >> (k << 3)) & 0xff];
#if N > 3
crc3 ^= BRAID_TABLE[k][(word3 >> (k << 3)) & 0xff];
#if N > 4
crc4 ^= BRAID_TABLE[k][(word4 >> (k << 3)) & 0xff];
#if N > 5
crc5 ^= BRAID_TABLE[k][(word5 >> (k << 3)) & 0xff];
#endif
#endif
#endif
#endif
#endif
}
}
/* Process the last block, combining the CRCs of the N braids at the same time. */
comb = crc_word(crc0 ^ words[0]);
#if N > 1
comb = crc_word(crc1 ^ words[1] ^ comb);
#if N > 2
comb = crc_word(crc2 ^ words[2] ^ comb);
#if N > 3
comb = crc_word(crc3 ^ words[3] ^ comb);
#if N > 4
comb = crc_word(crc4 ^ words[4] ^ comb);
#if N > 5
comb = crc_word(crc5 ^ words[5] ^ comb);
#endif
#endif
#endif
#endif
#endif
words += N;
Assert(comb <= UINT32_MAX, "comb should fit in uint32_t");
c = (uint32_t)ZSWAPWORD(comb);
/* Update the pointer to the remaining bytes to process. */
buf = (const unsigned char *)words;
}
#endif /* W */
/* Complete the computation of the CRC on any remaining bytes. */
while (len >= 8) {
len -= 8;
DO8;
}
while (len) {
len--;
DO1;
}
/* Return the CRC, post-conditioned. */
return c ^ 0xffffffff;
}
|
