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crc32.c
Go to the documentation of this file.
1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010 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
22 #ifdef MAKECRCH
23 # include <stdio.h>
24 # ifndef DYNAMIC_CRC_TABLE
25 # define DYNAMIC_CRC_TABLE
26 # endif /* !DYNAMIC_CRC_TABLE */
27 #endif /* MAKECRCH */
28
29 #include "zutil.h" /* for STDC and FAR definitions */
30
31 #define local static
32
33 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
34 #ifndef NOBYFOUR
35 # ifdef STDC /* need ANSI C limits.h to determine sizes */
36 # include <limits.h>
37 # define BYFOUR
38 # if (UINT_MAX == 0xffffffffUL)
39 typedef unsigned int u4;
40 # else
41 # if (ULONG_MAX == 0xffffffffUL)
42 typedef unsigned long u4;
43 # else
44 # if (USHRT_MAX == 0xffffffffUL)
45 typedef unsigned short u4;
46 # else
47 # undef BYFOUR /* can't find a four-byte integer type! */
48 # endif
49 # endif
50 # endif
51 # endif /* STDC */
52 #endif /* !NOBYFOUR */
53
54 /* Definitions for doing the crc four data bytes at a time. */
55 #ifdef BYFOUR
56 # define REV(w) ((((w)>>24)&0xff)+(((w)>>8)&0xff00)+ \
57 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
58 local unsigned long crc32_little OF((unsigned long,
59 const unsigned char FAR *, unsigned));
60 local unsigned long crc32_big OF((unsigned long,
61 const unsigned char FAR *, unsigned));
62 # define TBLS 8
63 #else
64 # define TBLS 1
65 #endif /* BYFOUR */
66
67 /* Local functions for crc concatenation */
68 local unsigned long gf2_matrix_times OF((unsigned long *mat,
69 unsigned long vec));
70 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
71 local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2);
72
73
74 #ifdef DYNAMIC_CRC_TABLE
75
76 local volatile int crc_table_empty = 1;
77 local unsigned long FAR crc_table[TBLS][256];
78 local void make_crc_table OF((void));
79 #ifdef MAKECRCH
80 local void write_table OF((FILE *, const unsigned long FAR *));
81 #endif /* MAKECRCH */
82 /*
83 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
84 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.
85
86 Polynomials over GF(2) are represented in binary, one bit per coefficient,
87 with the lowest powers in the most significant bit. Then adding polynomials
88 is just exclusive-or, and multiplying a polynomial by x is a right shift by
89 one. If we call the above polynomial p, and represent a byte as the
90 polynomial q, also with the lowest power in the most significant bit (so the
91 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
92 where a mod b means the remainder after dividing a by b.
93
94 This calculation is done using the shift-register method of multiplying and
95 taking the remainder. The register is initialized to zero, and for each
96 incoming bit, x^32 is added mod p to the register if the bit is a one (where
97 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
98 x (which is shifting right by one and adding x^32 mod p if the bit shifted
99 out is a one). We start with the highest power (least significant bit) of
100 q and repeat for all eight bits of q.
101
102 The first table is simply the CRC of all possible eight bit values. This is
103 all the information needed to generate CRCs on data a byte at a time for all
104 combinations of CRC register values and incoming bytes. The remaining tables
105 allow for word-at-a-time CRC calculation for both big-endian and little-
106 endian machines, where a word is four bytes.
107 */
108 local void make_crc_table()
109 {
110 unsigned long c;
111 int n, k;
112 unsigned long poly; /* polynomial exclusive-or pattern */
113 /* terms of polynomial defining this crc (except x^32): */
114 static volatile int first = 1; /* flag to limit concurrent making */
115 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
116
117 /* See if another task is already doing this (not thread-safe, but better
118 than nothing -- significantly reduces duration of vulnerability in
119 case the advice about DYNAMIC_CRC_TABLE is ignored) */
120 if (first) {
121 first = 0;
122
123 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
124 poly = 0UL;
125 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
126 poly |= 1UL << (31 - p[n]);
127
128 /* generate a crc for every 8-bit value */
129 for (n = 0; n < 256; n++) {
130 c = (unsigned long)n;
131 for (k = 0; k < 8; k++)
132 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
133 crc_table[0][n] = c;
134 }
135
136 #ifdef BYFOUR
137 /* generate crc for each value followed by one, two, and three zeros,
138 and then the byte reversal of those as well as the first table */
139 for (n = 0; n < 256; n++) {
140 c = crc_table[0][n];
141 crc_table[4][n] = REV(c);
142 for (k = 1; k < 4; k++) {
143 c = crc_table[0][c & 0xff] ^ (c >> 8);
144 crc_table[k][n] = c;
145 crc_table[k + 4][n] = REV(c);
146 }
147 }
148 #endif /* BYFOUR */
149
150 crc_table_empty = 0;
151 }
152 else { /* not first */
153 /* wait for the other guy to finish (not efficient, but rare) */
154 while (crc_table_empty)
155 ;
156 }
157
158 #ifdef MAKECRCH
159 /* write out CRC tables to crc32.h */
160 {
161 FILE *out;
162
163 out = fopen("crc32.h", "w");
164 if (out == NULL) return;
165 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
166 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
167 fprintf(out, "local const unsigned long FAR ");
168 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
169 write_table(out, crc_table[0]);
170 # ifdef BYFOUR
171 fprintf(out, "#ifdef BYFOUR\n");
172 for (k = 1; k < 8; k++) {
173 fprintf(out, " },\n {\n");
174 write_table(out, crc_table[k]);
175 }
176 fprintf(out, "#endif\n");
177 # endif /* BYFOUR */
178 fprintf(out, " }\n};\n");
179 fclose(out);
180 }
181 #endif /* MAKECRCH */
182 }
183
184 #ifdef MAKECRCH
185 local void write_table(out, table)
186 FILE *out;
187 const unsigned long FAR *table;
188 {
189 int n;
190
191 for (n = 0; n < 256; n++)
192 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
193 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
194 }
195 #endif /* MAKECRCH */
196
197 #else /* !DYNAMIC_CRC_TABLE */
198 /* ========================================================================
199 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
200 */
201 #include "crc32.h"
202 #endif /* DYNAMIC_CRC_TABLE */
203
204 /* =========================================================================
205 * This function can be used by asm versions of crc32()
206 */
207 const unsigned long FAR * ZEXPORT get_crc_table()
208 {
209 #ifdef DYNAMIC_CRC_TABLE
210 if (crc_table_empty)
211 make_crc_table();
212 #endif /* DYNAMIC_CRC_TABLE */
213 return (const unsigned long FAR *)crc_table;
214 }
215
216 /* ========================================================================= */
217 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
218 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
219
220 /* ========================================================================= */
221 unsigned long ZEXPORT crc32(crc, buf, len)
222 unsigned long crc;
223 const unsigned char FAR *buf;
224 uInt len;
225 {
226 if (buf == Z_NULL) return 0UL;
227
228 #ifdef DYNAMIC_CRC_TABLE
229 if (crc_table_empty)
230 make_crc_table();
231 #endif /* DYNAMIC_CRC_TABLE */
232
233 #ifdef BYFOUR
234 if (sizeof(void *) == sizeof(ptrdiff_t)) {
235 u4 endian;
236
237 endian = 1;
238 if (*((unsigned char *)(&endian)))
239 return crc32_little(crc, buf, len);
240 else
241 return crc32_big(crc, buf, len);
242 }
243 #endif /* BYFOUR */
244 crc = crc ^ 0xffffffffUL;
245 while (len >= 8) {
246 DO8;
247 len -= 8;
248 }
249 if (len) do {
250 DO1;
251 } while (--len);
252 return crc ^ 0xffffffffUL;
253 }
254
255 #ifdef BYFOUR
256
257 /* ========================================================================= */
258 #define DOLIT4 c ^= *buf4++; \
259 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
260 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
261 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
262
263 /* ========================================================================= */
264 local unsigned long crc32_little(crc, buf, len)
265 unsigned long crc;
266 const unsigned char FAR *buf;
267 unsigned len;
268 {
269 register u4 c;
270 register const u4 FAR *buf4;
271
272 c = (u4)crc;
273 c = ~c;
274 while (len && ((ptrdiff_t)buf & 3)) {
275 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
276 len--;
277 }
278
279 buf4 = (const u4 FAR *)(const void FAR *)buf;
280 while (len >= 32) {
281 DOLIT32;
282 len -= 32;
283 }
284 while (len >= 4) {
285 DOLIT4;
286 len -= 4;
287 }
288 buf = (const unsigned char FAR *)buf4;
289
290 if (len) do {
291 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
292 } while (--len);
293 c = ~c;
294 return (unsigned long)c;
295 }
296
297 /* ========================================================================= */
298 #define DOBIG4 c ^= *++buf4; \
299 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
300 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
301 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
302
303 /* ========================================================================= */
304 local unsigned long crc32_big(crc, buf, len)
305 unsigned long crc;
306 const unsigned char FAR *buf;
307 unsigned len;
308 {
309 register u4 c;
310 register const u4 FAR *buf4;
311
312 c = REV((u4)crc);
313 c = ~c;
314 while (len && ((ptrdiff_t)buf & 3)) {
315 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
316 len--;
317 }
318
319 buf4 = (const u4 FAR *)(const void FAR *)buf;
320 buf4--;
321 while (len >= 32) {
322 DOBIG32;
323 len -= 32;
324 }
325 while (len >= 4) {
326 DOBIG4;
327 len -= 4;
328 }
329 buf4++;
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)(REV(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 }
gf2_matrix_square
local void gf2_matrix_square(unsigned long *square, unsigned long *mat)
Definition: crc32.c:361
crc32_combine_
local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.c:372
GF2_DIM
#define GF2_DIM
Definition: crc32.c:341
z_off_t
#define z_off_t
Definition: zconf.h:383
z_off64_t
#define z_off64_t
Definition: zconf.h:400
gf2_matrix_times
local unsigned long gf2_matrix_times(unsigned long *mat, unsigned long vec)
Definition: crc32.c:344
uLong
unsigned long uLong
Definition: zconf.h:336
crc32.h
DO1
#define DO1
Definition: crc32.c:217
DO8
#define DO8
Definition: crc32.c:218
get_crc_table
const unsigned long FAR *ZEXPORT get_crc_table()
Definition: crc32.c:207
crc32_combine
uLong ZEXPORT crc32_combine(uLong crc1, uLong crc2, z_off_t len2)
Definition: crc32.c:428
FAR
#define FAR
Definition: jmorecfg.h:215
crc32
unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, uInt len)
Definition: crc32.c:221
crc32_combine64
uLong ZEXPORT crc32_combine64(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.c:436
crc_table
local const unsigned long FAR crc_table[TBLS][256]
Definition: crc32.h:5
local
#define local
Definition: crc32.c:31
Z_NULL
#define Z_NULL
Definition: zlib.h:208
OF
local unsigned long gf2_matrix_times OF((unsigned long *mat, unsigned long vec))
zutil.h
const
#define const
Definition: zconf.h:196
ZEXPORT
#define ZEXPORT
Definition: zconf.h:322
TBLS
#define TBLS
Definition: crc32.c:64
uInt
unsigned int uInt
Definition: zconf.h:335