source: Vago/zlib-1.2.8/crc32.c@ 1049

Last change on this file since 1049 was 1049, checked in by s10k, 8 years ago
File size: 12.9 KB
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1/* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010, 2011, 2012 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#define local static
34
35/* Definitions for doing the crc four data bytes at a time. */
36#if !defined(NOBYFOUR) && defined(Z_U4)
37# define BYFOUR
38#endif
39#ifdef BYFOUR
40 local unsigned long crc32_little OF((unsigned long,
41 const unsigned char FAR *, unsigned));
42 local unsigned long crc32_big OF((unsigned long,
43 const unsigned char FAR *, unsigned));
44# define TBLS 8
45#else
46# define TBLS 1
47#endif /* BYFOUR */
48
49/* Local functions for crc concatenation */
50local unsigned long gf2_matrix_times OF((unsigned long *mat,
51 unsigned long vec));
52local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
53local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
54
55
56#ifdef DYNAMIC_CRC_TABLE
57
58local volatile int crc_table_empty = 1;
59local z_crc_t FAR crc_table[TBLS][256];
60local void make_crc_table OF((void));
61#ifdef MAKECRCH
62 local void write_table OF((FILE *, const z_crc_t FAR *));
63#endif /* MAKECRCH */
64/*
65 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
66 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.
67
68 Polynomials over GF(2) are represented in binary, one bit per coefficient,
69 with the lowest powers in the most significant bit. Then adding polynomials
70 is just exclusive-or, and multiplying a polynomial by x is a right shift by
71 one. If we call the above polynomial p, and represent a byte as the
72 polynomial q, also with the lowest power in the most significant bit (so the
73 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
74 where a mod b means the remainder after dividing a by b.
75
76 This calculation is done using the shift-register method of multiplying and
77 taking the remainder. The register is initialized to zero, and for each
78 incoming bit, x^32 is added mod p to the register if the bit is a one (where
79 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
80 x (which is shifting right by one and adding x^32 mod p if the bit shifted
81 out is a one). We start with the highest power (least significant bit) of
82 q and repeat for all eight bits of q.
83
84 The first table is simply the CRC of all possible eight bit values. This is
85 all the information needed to generate CRCs on data a byte at a time for all
86 combinations of CRC register values and incoming bytes. The remaining tables
87 allow for word-at-a-time CRC calculation for both big-endian and little-
88 endian machines, where a word is four bytes.
89*/
90local void make_crc_table()
91{
92 z_crc_t c;
93 int n, k;
94 z_crc_t poly; /* polynomial exclusive-or pattern */
95 /* terms of polynomial defining this crc (except x^32): */
96 static volatile int first = 1; /* flag to limit concurrent making */
97 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
98
99 /* See if another task is already doing this (not thread-safe, but better
100 than nothing -- significantly reduces duration of vulnerability in
101 case the advice about DYNAMIC_CRC_TABLE is ignored) */
102 if (first) {
103 first = 0;
104
105 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
106 poly = 0;
107 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
108 poly |= (z_crc_t)1 << (31 - p[n]);
109
110 /* generate a crc for every 8-bit value */
111 for (n = 0; n < 256; n++) {
112 c = (z_crc_t)n;
113 for (k = 0; k < 8; k++)
114 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
115 crc_table[0][n] = c;
116 }
117
118#ifdef BYFOUR
119 /* generate crc for each value followed by one, two, and three zeros,
120 and then the byte reversal of those as well as the first table */
121 for (n = 0; n < 256; n++) {
122 c = crc_table[0][n];
123 crc_table[4][n] = ZSWAP32(c);
124 for (k = 1; k < 4; k++) {
125 c = crc_table[0][c & 0xff] ^ (c >> 8);
126 crc_table[k][n] = c;
127 crc_table[k + 4][n] = ZSWAP32(c);
128 }
129 }
130#endif /* BYFOUR */
131
132 crc_table_empty = 0;
133 }
134 else { /* not first */
135 /* wait for the other guy to finish (not efficient, but rare) */
136 while (crc_table_empty)
137 ;
138 }
139
140#ifdef MAKECRCH
141 /* write out CRC tables to crc32.h */
142 {
143 FILE *out;
144
145 out = fopen("crc32.h", "w");
146 if (out == NULL) return;
147 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
148 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
149 fprintf(out, "local const z_crc_t FAR ");
150 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
151 write_table(out, crc_table[0]);
152# ifdef BYFOUR
153 fprintf(out, "#ifdef BYFOUR\n");
154 for (k = 1; k < 8; k++) {
155 fprintf(out, " },\n {\n");
156 write_table(out, crc_table[k]);
157 }
158 fprintf(out, "#endif\n");
159# endif /* BYFOUR */
160 fprintf(out, " }\n};\n");
161 fclose(out);
162 }
163#endif /* MAKECRCH */
164}
165
166#ifdef MAKECRCH
167local void write_table(out, table)
168 FILE *out;
169 const z_crc_t FAR *table;
170{
171 int n;
172
173 for (n = 0; n < 256; n++)
174 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
175 (unsigned long)(table[n]),
176 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
177}
178#endif /* MAKECRCH */
179
180#else /* !DYNAMIC_CRC_TABLE */
181/* ========================================================================
182 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
183 */
184#include "crc32.h"
185#endif /* DYNAMIC_CRC_TABLE */
186
187/* =========================================================================
188 * This function can be used by asm versions of crc32()
189 */
190const z_crc_t FAR * ZEXPORT get_crc_table()
191{
192#ifdef DYNAMIC_CRC_TABLE
193 if (crc_table_empty)
194 make_crc_table();
195#endif /* DYNAMIC_CRC_TABLE */
196 return (const z_crc_t FAR *)crc_table;
197}
198
199/* ========================================================================= */
200#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
201#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
202
203/* ========================================================================= */
204unsigned long ZEXPORT crc32(crc, buf, len)
205 unsigned long crc;
206 const unsigned char FAR *buf;
207 uInt len;
208{
209 if (buf == Z_NULL) return 0UL;
210
211#ifdef DYNAMIC_CRC_TABLE
212 if (crc_table_empty)
213 make_crc_table();
214#endif /* DYNAMIC_CRC_TABLE */
215
216#ifdef BYFOUR
217 if (sizeof(void *) == sizeof(ptrdiff_t)) {
218 z_crc_t endian;
219
220 endian = 1;
221 if (*((unsigned char *)(&endian)))
222 return crc32_little(crc, buf, len);
223 else
224 return crc32_big(crc, buf, len);
225 }
226#endif /* BYFOUR */
227 crc = crc ^ 0xffffffffUL;
228 while (len >= 8) {
229 DO8;
230 len -= 8;
231 }
232 if (len) do {
233 DO1;
234 } while (--len);
235 return crc ^ 0xffffffffUL;
236}
237
238#ifdef BYFOUR
239
240/* ========================================================================= */
241#define DOLIT4 c ^= *buf4++; \
242 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
243 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
244#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
245
246/* ========================================================================= */
247local unsigned long crc32_little(crc, buf, len)
248 unsigned long crc;
249 const unsigned char FAR *buf;
250 unsigned len;
251{
252 register z_crc_t c;
253 register const z_crc_t FAR *buf4;
254
255 c = (z_crc_t)crc;
256 c = ~c;
257 while (len && ((ptrdiff_t)buf & 3)) {
258 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
259 len--;
260 }
261
262 buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
263 while (len >= 32) {
264 DOLIT32;
265 len -= 32;
266 }
267 while (len >= 4) {
268 DOLIT4;
269 len -= 4;
270 }
271 buf = (const unsigned char FAR *)buf4;
272
273 if (len) do {
274 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
275 } while (--len);
276 c = ~c;
277 return (unsigned long)c;
278}
279
280/* ========================================================================= */
281#define DOBIG4 c ^= *++buf4; \
282 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
283 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
284#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
285
286/* ========================================================================= */
287local unsigned long crc32_big(crc, buf, len)
288 unsigned long crc;
289 const unsigned char FAR *buf;
290 unsigned len;
291{
292 register z_crc_t c;
293 register const z_crc_t FAR *buf4;
294
295 c = ZSWAP32((z_crc_t)crc);
296 c = ~c;
297 while (len && ((ptrdiff_t)buf & 3)) {
298 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
299 len--;
300 }
301
302 buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
303 buf4--;
304 while (len >= 32) {
305 DOBIG32;
306 len -= 32;
307 }
308 while (len >= 4) {
309 DOBIG4;
310 len -= 4;
311 }
312 buf4++;
313 buf = (const unsigned char FAR *)buf4;
314
315 if (len) do {
316 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
317 } while (--len);
318 c = ~c;
319 return (unsigned long)(ZSWAP32(c));
320}
321
322#endif /* BYFOUR */
323
324#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
325
326/* ========================================================================= */
327local unsigned long gf2_matrix_times(mat, vec)
328 unsigned long *mat;
329 unsigned long vec;
330{
331 unsigned long sum;
332
333 sum = 0;
334 while (vec) {
335 if (vec & 1)
336 sum ^= *mat;
337 vec >>= 1;
338 mat++;
339 }
340 return sum;
341}
342
343/* ========================================================================= */
344local void gf2_matrix_square(square, mat)
345 unsigned long *square;
346 unsigned long *mat;
347{
348 int n;
349
350 for (n = 0; n < GF2_DIM; n++)
351 square[n] = gf2_matrix_times(mat, mat[n]);
352}
353
354/* ========================================================================= */
355local uLong crc32_combine_(crc1, crc2, len2)
356 uLong crc1;
357 uLong crc2;
358 z_off64_t len2;
359{
360 int n;
361 unsigned long row;
362 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
363 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
364
365 /* degenerate case (also disallow negative lengths) */
366 if (len2 <= 0)
367 return crc1;
368
369 /* put operator for one zero bit in odd */
370 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
371 row = 1;
372 for (n = 1; n < GF2_DIM; n++) {
373 odd[n] = row;
374 row <<= 1;
375 }
376
377 /* put operator for two zero bits in even */
378 gf2_matrix_square(even, odd);
379
380 /* put operator for four zero bits in odd */
381 gf2_matrix_square(odd, even);
382
383 /* apply len2 zeros to crc1 (first square will put the operator for one
384 zero byte, eight zero bits, in even) */
385 do {
386 /* apply zeros operator for this bit of len2 */
387 gf2_matrix_square(even, odd);
388 if (len2 & 1)
389 crc1 = gf2_matrix_times(even, crc1);
390 len2 >>= 1;
391
392 /* if no more bits set, then done */
393 if (len2 == 0)
394 break;
395
396 /* another iteration of the loop with odd and even swapped */
397 gf2_matrix_square(odd, even);
398 if (len2 & 1)
399 crc1 = gf2_matrix_times(odd, crc1);
400 len2 >>= 1;
401
402 /* if no more bits set, then done */
403 } while (len2 != 0);
404
405 /* return combined crc */
406 crc1 ^= crc2;
407 return crc1;
408}
409
410/* ========================================================================= */
411uLong ZEXPORT crc32_combine(crc1, crc2, len2)
412 uLong crc1;
413 uLong crc2;
414 z_off_t len2;
415{
416 return crc32_combine_(crc1, crc2, len2);
417}
418
419uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
420 uLong crc1;
421 uLong crc2;
422 z_off64_t len2;
423{
424 return crc32_combine_(crc1, crc2, len2);
425}
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