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crc32.c
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1/* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010, 2011, 2012, 2016 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 *
5 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
6 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
7 * tables for updating the shift register in one step with three exclusive-ors
8 * instead of four steps with four exclusive-ors. This results in about a
9 * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
10 */
11
12/* @(#) $Id$ */
13
14/*
15 Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
16 protection on the static variables used to control the first-use generation
17 of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
18 first call get_crc_table() to initialize the tables before allowing more than
19 one thread to use crc32().
20
21 DYNAMIC_CRC_TABLE and MAKECRCH can be #defined to write out crc32.h.
22 */
23
24#ifdef MAKECRCH
25# include <stdio.h>
26# ifndef DYNAMIC_CRC_TABLE
27# define DYNAMIC_CRC_TABLE
28# endif /* !DYNAMIC_CRC_TABLE */
29#endif /* MAKECRCH */
30
31#include "zutil.h" /* for STDC and FAR definitions */
32
33/* Definitions for doing the crc four data bytes at a time. */
34#if !defined(NOBYFOUR) && defined(Z_U4)
35# define BYFOUR
36#endif
37#ifdef BYFOUR
38 local unsigned long crc32_little OF((unsigned long,
39 const unsigned char FAR *, z_size_t));
40 local unsigned long crc32_big OF((unsigned long,
41 const unsigned char FAR *, z_size_t));
42# define TBLS 8
43#else
44# define TBLS 1
45#endif /* BYFOUR */
46
47/* Local functions for crc concatenation */
48 local unsigned long gf2_matrix_times OF((unsigned long *mat,
49 unsigned long vec));
50 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
51 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
52
53
54#ifdef DYNAMIC_CRC_TABLE
55
56 local volatile int crc_table_empty = 1;
57 local z_crc_t FAR crc_table[TBLS][256];
58 local void make_crc_table OF((void));
59#ifdef MAKECRCH
60 local void write_table OF((FILE *, const z_crc_t FAR *));
61#endif /* MAKECRCH */
62/*
63 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
64 x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
65
66 Polynomials over GF(2) are represented in binary, one bit per coefficient,
67 with the lowest powers in the most significant bit. Then adding polynomials
68 is just exclusive-or, and multiplying a polynomial by x is a right shift by
69 one. If we call the above polynomial p, and represent a byte as the
70 polynomial q, also with the lowest power in the most significant bit (so the
71 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
72 where a mod b means the remainder after dividing a by b.
73
74 This calculation is done using the shift-register method of multiplying and
75 taking the remainder. The register is initialized to zero, and for each
76 incoming bit, x^32 is added mod p to the register if the bit is a one (where
77 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
78 x (which is shifting right by one and adding x^32 mod p if the bit shifted
79 out is a one). We start with the highest power (least significant bit) of
80 q and repeat for all eight bits of q.
81
82 The first table is simply the CRC of all possible eight bit values. This is
83 all the information needed to generate CRCs on data a byte at a time for all
84 combinations of CRC register values and incoming bytes. The remaining tables
85 allow for word-at-a-time CRC calculation for both big-endian and little-
86 endian machines, where a word is four bytes.
87*/
88 local void make_crc_table()
89{
90 z_crc_t c;
91 int n, k;
92 z_crc_t poly; /* polynomial exclusive-or pattern */
93 /* terms of polynomial defining this crc (except x^32): */
94 static volatile int first = 1; /* flag to limit concurrent making */
95 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
96
97 /* See if another task is already doing this (not thread-safe, but better
98 than nothing -- significantly reduces duration of vulnerability in
99 case the advice about DYNAMIC_CRC_TABLE is ignored) */
100 if (first) {
101 first = 0;
102
103 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
104 poly = 0;
105 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
106 poly |= (z_crc_t)1 << (31 - p[n]);
107
108 /* generate a crc for every 8-bit value */
109 for (n = 0; n < 256; n++) {
110 c = (z_crc_t)n;
111 for (k = 0; k < 8; k++)
112 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
113 crc_table[0][n] = c;
114 }
115
116#ifdef BYFOUR
117 /* generate crc for each value followed by one, two, and three zeros,
118 and then the byte reversal of those as well as the first table */
119 for (n = 0; n < 256; n++) {
120 c = crc_table[0][n];
121 crc_table[4][n] = ZSWAP32(c);
122 for (k = 1; k < 4; k++) {
123 c = crc_table[0][c & 0xff] ^ (c >> 8);
124 crc_table[k][n] = c;
125 crc_table[k + 4][n] = ZSWAP32(c);
126 }
127 }
128#endif /* BYFOUR */
129
130 crc_table_empty = 0;
131 }
132 else { /* not first */
133 /* wait for the other guy to finish (not efficient, but rare) */
134 while (crc_table_empty)
135 ;
136 }
137
138#ifdef MAKECRCH
139 /* write out CRC tables to crc32.h */
140 {
141 FILE *out;
142
143 out = fopen("crc32.h", "w");
144 if (out == NULL) return;
145 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
146 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
147 fprintf(out, "local const z_crc_t FAR ");
148 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
149 write_table(out, crc_table[0]);
150# ifdef BYFOUR
151 fprintf(out, "#ifdef BYFOUR\n");
152 for (k = 1; k < 8; k++) {
153 fprintf(out, " },\n {\n");
154 write_table(out, crc_table[k]);
155 }
156 fprintf(out, "#endif\n");
157# endif /* BYFOUR */
158 fprintf(out, " }\n};\n");
159 fclose(out);
160 }
161#endif /* MAKECRCH */
162}
163
164#ifdef MAKECRCH
165 local void write_table(out, table)
166 FILE *out;
167 const z_crc_t FAR *table;
168{
169 int n;
170
171 for (n = 0; n < 256; n++)
172 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
173 (unsigned long)(table[n]),
174 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
175}
176#endif /* MAKECRCH */
177
178#else /* !DYNAMIC_CRC_TABLE */
179/* ========================================================================
180 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
181 */
182#include "crc32.h"
183#endif /* DYNAMIC_CRC_TABLE */
184
185/* =========================================================================
186 * This function can be used by asm versions of crc32()
187 */
188 const z_crc_t FAR * ZEXPORT get_crc_table()
189{
190#ifdef DYNAMIC_CRC_TABLE
191 if (crc_table_empty)
192 make_crc_table();
193#endif /* DYNAMIC_CRC_TABLE */
194 return (const z_crc_t FAR *)crc_table;
195}
196
197/* ========================================================================= */
198#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
199#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
200
201/* ========================================================================= */
202 unsigned long ZEXPORT crc32_z(crc, buf, len)
203 unsigned long crc;
204 const unsigned char FAR *buf;
205 z_size_t len;
206{
207 if (buf == Z_NULL) return 0UL;
208
209#ifdef DYNAMIC_CRC_TABLE
210 if (crc_table_empty)
211 make_crc_table();
212#endif /* DYNAMIC_CRC_TABLE */
213
214#ifdef BYFOUR
215 if (sizeof(void *) == sizeof(ptrdiff_t)) {
216 z_crc_t endian;
217
218 endian = 1;
219 if (*((unsigned char *)(&endian)))
220 return crc32_little(crc, buf, len);
221 else
222 return crc32_big(crc, buf, len);
223 }
224#endif /* BYFOUR */
225 crc = crc ^ 0xffffffffUL;
226 while (len >= 8) {
227 DO8;
228 len -= 8;
229 }
230 if (len) do {
231 DO1;
232 } while (--len);
233 return crc ^ 0xffffffffUL;
234}
235
236/* ========================================================================= */
237 unsigned long ZEXPORT crc32(crc, buf, len)
238 unsigned long crc;
239 const unsigned char FAR *buf;
240 uInt len;
241{
242 return crc32_z(crc, buf, len);
243}
244
245#ifdef BYFOUR
246
247/*
248 This BYFOUR code accesses the passed unsigned char * buffer with a 32-bit
249 integer pointer type. This violates the strict aliasing rule, where a
250 compiler can assume, for optimization purposes, that two pointers to
251 fundamentally different types won't ever point to the same memory. This can
252 manifest as a problem only if one of the pointers is written to. This code
253 only reads from those pointers. So long as this code remains isolated in
254 this compilation unit, there won't be a problem. For this reason, this code
255 should not be copied and pasted into a compilation unit in which other code
256 writes to the buffer that is passed to these routines.
257 */
258
259/* ========================================================================= */
260#define DOLIT4 c ^= *buf4++; \
261 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
262 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
263#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
264
265/* ========================================================================= */
266 local unsigned long crc32_little(crc, buf, len)
267 unsigned long crc;
268 const unsigned char FAR *buf;
269 z_size_t len;
270{
271 register z_crc_t c;
272 register const z_crc_t FAR *buf4;
273
274 c = (z_crc_t)crc;
275 c = ~c;
276 while (len && ((ptrdiff_t)buf & 3)) {
277 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
278 len--;
279 }
280
281 buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
282 while (len >= 32) {
283 DOLIT32;
284 len -= 32;
285 }
286 while (len >= 4) {
287 DOLIT4;
288 len -= 4;
289 }
290 buf = (const unsigned char FAR *)buf4;
291
292 if (len) do {
293 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
294 } while (--len);
295 c = ~c;
296 return (unsigned long)c;
297}
298
299/* ========================================================================= */
300#define DOBIG4 c ^= *buf4++; \
301 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
302 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
303#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
304
305/* ========================================================================= */
306 local unsigned long crc32_big(crc, buf, len)
307 unsigned long crc;
308 const unsigned char FAR *buf;
309 z_size_t len;
310{
311 register z_crc_t c;
312 register const z_crc_t FAR *buf4;
313
314 c = ZSWAP32((z_crc_t)crc);
315 c = ~c;
316 while (len && ((ptrdiff_t)buf & 3)) {
317 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
318 len--;
319 }
320
321 buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
322 while (len >= 32) {
323 DOBIG32;
324 len -= 32;
325 }
326 while (len >= 4) {
327 DOBIG4;
328 len -= 4;
329 }
330 buf = (const unsigned char FAR *)buf4;
331
332 if (len) do {
333 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
334 } while (--len);
335 c = ~c;
336 return (unsigned long)(ZSWAP32(c));
337}
338
339#endif /* BYFOUR */
340
341#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
342
343/* ========================================================================= */
344 local unsigned long gf2_matrix_times(mat, vec)
345 unsigned long *mat;
346 unsigned long vec;
347{
348 unsigned long sum;
349
350 sum = 0;
351 while (vec) {
352 if (vec & 1)
353 sum ^= *mat;
354 vec >>= 1;
355 mat++;
356 }
357 return sum;
358}
359
360/* ========================================================================= */
361 local void gf2_matrix_square(square, mat)
362 unsigned long *square;
363 unsigned long *mat;
364{
365 int n;
366
367 for (n = 0; n < GF2_DIM; n++)
368 square[n] = gf2_matrix_times(mat, mat[n]);
369}
370
371/* ========================================================================= */
372 local uLong crc32_combine_(crc1, crc2, len2)
373 uLong crc1;
374 uLong crc2;
375 z_off64_t len2;
376{
377 int n;
378 unsigned long row;
379 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
380 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
381
382 /* degenerate case (also disallow negative lengths) */
383 if (len2 <= 0)
384 return crc1;
385
386 /* put operator for one zero bit in odd */
387 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
388 row = 1;
389 for (n = 1; n < GF2_DIM; n++) {
390 odd[n] = row;
391 row <<= 1;
392 }
393
394 /* put operator for two zero bits in even */
395 gf2_matrix_square(even, odd);
396
397 /* put operator for four zero bits in odd */
398 gf2_matrix_square(odd, even);
399
400 /* apply len2 zeros to crc1 (first square will put the operator for one
401 zero byte, eight zero bits, in even) */
402 do {
403 /* apply zeros operator for this bit of len2 */
404 gf2_matrix_square(even, odd);
405 if (len2 & 1)
406 crc1 = gf2_matrix_times(even, crc1);
407 len2 >>= 1;
408
409 /* if no more bits set, then done */
410 if (len2 == 0)
411 break;
412
413 /* another iteration of the loop with odd and even swapped */
414 gf2_matrix_square(odd, even);
415 if (len2 & 1)
416 crc1 = gf2_matrix_times(odd, crc1);
417 len2 >>= 1;
418
419 /* if no more bits set, then done */
420 } while (len2 != 0);
421
422 /* return combined crc */
423 crc1 ^= crc2;
424 return crc1;
425}
426
427/* ========================================================================= */
428 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
429 uLong crc1;
430 uLong crc2;
431 z_off_t len2;
432{
433 return crc32_combine_(crc1, crc2, len2);
434}
435
436 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
437 uLong crc1;
438 uLong crc2;
439 z_off64_t len2;
440{
441 return crc32_combine_(crc1, crc2, len2);
442}
TBLS
#define TBLS
Definition: crc32.c:44
get_crc_table
const z_crc_t FAR *ZEXPORT get_crc_table()
Definition: crc32.c:188
GF2_DIM
#define GF2_DIM
Definition: crc32.c:341
crc32_z
unsigned long ZEXPORT crc32_z(unsigned long crc, const unsigned char FAR *buf, z_size_t len)
Definition: crc32.c:202
gf2_matrix_times
unsigned long gf2_matrix_times(unsigned long *mat, unsigned long vec)
Definition: crc32.c:344
OF
unsigned long gf2_matrix_times OF((unsigned long *mat, unsigned long vec))
crc32_combine
uLong ZEXPORT crc32_combine(uLong crc1, uLong crc2, z_off_t len2)
Definition: crc32.c:428
crc32_combine64
uLong ZEXPORT crc32_combine64(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.c:436
crc32_combine_
uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.c:372
DO8
#define DO8
Definition: crc32.c:199
crc32
unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, uInt len)
Definition: crc32.c:237
gf2_matrix_square
void gf2_matrix_square(unsigned long *square, unsigned long *mat)
Definition: crc32.c:361
DO1
#define DO1
Definition: crc32.c:198
crc32.h
crc_table
const z_crc_t FAR crc_table[TBLS][256]
Definition: crc32.h:5
local
#define local
Definition: gzguts.h:114
ZEXPORT
#define ZEXPORT
Definition: zconf.h:380
z_crc_t
unsigned long z_crc_t
Definition: zconf.h:431
uInt
unsigned int uInt
Definition: zconf.h:393
z_off_t
#define z_off_t
Definition: zconf.h:504
z_off64_t
#define z_off64_t
Definition: zconf.h:513
z_size_t
unsigned long z_size_t
Definition: zconf.h:250
uLong
unsigned long uLong
Definition: zconf.h:394
FAR
#define FAR
Definition: zconf.h:387
Z_NULL
#define Z_NULL
Definition: zlib.h:212
zutil.h
ZSWAP32
#define ZSWAP32(q)
Definition: zutil.h:268