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c801d85f 1/* crc32.c -- compute the CRC-32 of a data stream
41faf807 2 * Copyright (C) 1995-2005 Mark Adler
e6ebb514 3 * For conditions of distribution and use, see copyright notice in zlib.h
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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
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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.
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10 */
11
12/* @(#) $Id$ */
13
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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
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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 */
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30
31#define local static
32
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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)+(((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
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67/* Local functions for crc concatenation */
68local unsigned long gf2_matrix_times OF((unsigned long *mat,
69 unsigned long vec));
70local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
71
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72#ifdef DYNAMIC_CRC_TABLE
73
ba0052f3 74local volatile int crc_table_empty = 1;
51dbdf87 75local unsigned long FAR crc_table[TBLS][256];
c801d85f 76local void make_crc_table OF((void));
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77#ifdef MAKECRCH
78 local void write_table OF((FILE *, const unsigned long FAR *));
79#endif /* MAKECRCH */
c801d85f 80/*
51dbdf87 81 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
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82 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.
83
84 Polynomials over GF(2) are represented in binary, one bit per coefficient,
85 with the lowest powers in the most significant bit. Then adding polynomials
86 is just exclusive-or, and multiplying a polynomial by x is a right shift by
87 one. If we call the above polynomial p, and represent a byte as the
88 polynomial q, also with the lowest power in the most significant bit (so the
89 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
90 where a mod b means the remainder after dividing a by b.
91
92 This calculation is done using the shift-register method of multiplying and
93 taking the remainder. The register is initialized to zero, and for each
94 incoming bit, x^32 is added mod p to the register if the bit is a one (where
95 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
96 x (which is shifting right by one and adding x^32 mod p if the bit shifted
97 out is a one). We start with the highest power (least significant bit) of
98 q and repeat for all eight bits of q.
99
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100 The first table is simply the CRC of all possible eight bit values. This is
101 all the information needed to generate CRCs on data a byte at a time for all
102 combinations of CRC register values and incoming bytes. The remaining tables
103 allow for word-at-a-time CRC calculation for both big-endian and little-
104 endian machines, where a word is four bytes.
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105*/
106local void make_crc_table()
107{
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108 unsigned long c;
109 int n, k;
ba0052f3 110 unsigned long poly; /* polynomial exclusive-or pattern */
51dbdf87 111 /* terms of polynomial defining this crc (except x^32): */
ba0052f3 112 static volatile int first = 1; /* flag to limit concurrent making */
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113 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
114
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115 /* See if another task is already doing this (not thread-safe, but better
116 than nothing -- significantly reduces duration of vulnerability in
117 case the advice about DYNAMIC_CRC_TABLE is ignored) */
118 if (first) {
119 first = 0;
120
121 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
122 poly = 0UL;
123 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
124 poly |= 1UL << (31 - p[n]);
125
126 /* generate a crc for every 8-bit value */
127 for (n = 0; n < 256; n++) {
128 c = (unsigned long)n;
129 for (k = 0; k < 8; k++)
130 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
131 crc_table[0][n] = c;
132 }
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133
134#ifdef BYFOUR
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135 /* generate crc for each value followed by one, two, and three zeros,
136 and then the byte reversal of those as well as the first table */
137 for (n = 0; n < 256; n++) {
138 c = crc_table[0][n];
139 crc_table[4][n] = REV(c);
140 for (k = 1; k < 4; k++) {
141 c = crc_table[0][c & 0xff] ^ (c >> 8);
142 crc_table[k][n] = c;
143 crc_table[k + 4][n] = REV(c);
144 }
51dbdf87 145 }
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146#endif /* BYFOUR */
147
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148 crc_table_empty = 0;
149 }
150 else { /* not first */
151 /* wait for the other guy to finish (not efficient, but rare) */
152 while (crc_table_empty)
153 ;
154 }
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155
156#ifdef MAKECRCH
157 /* write out CRC tables to crc32.h */
158 {
159 FILE *out;
160
161 out = fopen("crc32.h", "w");
162 if (out == NULL) return;
163 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
164 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
165 fprintf(out, "local const unsigned long FAR ");
166 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
167 write_table(out, crc_table[0]);
168# ifdef BYFOUR
169 fprintf(out, "#ifdef BYFOUR\n");
170 for (k = 1; k < 8; k++) {
171 fprintf(out, " },\n {\n");
172 write_table(out, crc_table[k]);
173 }
174 fprintf(out, "#endif\n");
175# endif /* BYFOUR */
176 fprintf(out, " }\n};\n");
177 fclose(out);
178 }
179#endif /* MAKECRCH */
c801d85f 180}
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181
182#ifdef MAKECRCH
183local void write_table(out, table)
184 FILE *out;
185 const unsigned long FAR *table;
186{
187 int n;
188
189 for (n = 0; n < 256; n++)
190 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
191 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
192}
193#endif /* MAKECRCH */
194
195#else /* !DYNAMIC_CRC_TABLE */
c801d85f 196/* ========================================================================
51dbdf87 197 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
c801d85f 198 */
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199#include "crc32.h"
200#endif /* DYNAMIC_CRC_TABLE */
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201
202/* =========================================================================
203 * This function can be used by asm versions of crc32()
204 */
51dbdf87 205const unsigned long FAR * ZEXPORT get_crc_table()
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206{
207#ifdef DYNAMIC_CRC_TABLE
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208 if (crc_table_empty)
209 make_crc_table();
51dbdf87 210#endif /* DYNAMIC_CRC_TABLE */
ba0052f3 211 return (const unsigned long FAR *)crc_table;
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212}
213
214/* ========================================================================= */
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215#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
216#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
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217
218/* ========================================================================= */
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219unsigned long ZEXPORT crc32(crc, buf, len)
220 unsigned long crc;
221 const unsigned char FAR *buf;
222 unsigned len;
c801d85f 223{
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224 if (buf == Z_NULL) return 0UL;
225
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226#ifdef DYNAMIC_CRC_TABLE
227 if (crc_table_empty)
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228 make_crc_table();
229#endif /* DYNAMIC_CRC_TABLE */
230
231#ifdef BYFOUR
232 if (sizeof(void *) == sizeof(ptrdiff_t)) {
233 u4 endian;
234
235 endian = 1;
236 if (*((unsigned char *)(&endian)))
237 return crc32_little(crc, buf, len);
238 else
239 return crc32_big(crc, buf, len);
240 }
241#endif /* BYFOUR */
242 crc = crc ^ 0xffffffffUL;
243 while (len >= 8) {
244 DO8;
245 len -= 8;
246 }
247 if (len) do {
248 DO1;
249 } while (--len);
250 return crc ^ 0xffffffffUL;
251}
252
253#ifdef BYFOUR
254
255/* ========================================================================= */
256#define DOLIT4 c ^= *buf4++; \
257 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
258 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
259#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
260
261/* ========================================================================= */
262local unsigned long crc32_little(crc, buf, len)
263 unsigned long crc;
264 const unsigned char FAR *buf;
265 unsigned len;
266{
267 register u4 c;
268 register const u4 FAR *buf4;
269
270 c = (u4)crc;
271 c = ~c;
272 while (len && ((ptrdiff_t)buf & 3)) {
273 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
274 len--;
275 }
276
41faf807 277 buf4 = (const u4 FAR *)(const void FAR *)buf;
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278 while (len >= 32) {
279 DOLIT32;
280 len -= 32;
281 }
282 while (len >= 4) {
283 DOLIT4;
284 len -= 4;
285 }
286 buf = (const unsigned char FAR *)buf4;
287
288 if (len) do {
289 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
290 } while (--len);
291 c = ~c;
292 return (unsigned long)c;
293}
294
295/* ========================================================================= */
296#define DOBIG4 c ^= *++buf4; \
297 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
298 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
299#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
300
301/* ========================================================================= */
302local unsigned long crc32_big(crc, buf, len)
303 unsigned long crc;
304 const unsigned char FAR *buf;
305 unsigned len;
306{
307 register u4 c;
308 register const u4 FAR *buf4;
309
310 c = REV((u4)crc);
311 c = ~c;
312 while (len && ((ptrdiff_t)buf & 3)) {
313 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
314 len--;
315 }
316
41faf807 317 buf4 = (const u4 FAR *)(const void FAR *)buf;
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318 buf4--;
319 while (len >= 32) {
320 DOBIG32;
321 len -= 32;
c801d85f 322 }
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323 while (len >= 4) {
324 DOBIG4;
325 len -= 4;
326 }
327 buf4++;
328 buf = (const unsigned char FAR *)buf4;
329
c801d85f 330 if (len) do {
51dbdf87 331 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
c801d85f 332 } while (--len);
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333 c = ~c;
334 return (unsigned long)(REV(c));
c801d85f 335}
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336
337#endif /* BYFOUR */
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338
339#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
340
341/* ========================================================================= */
342local unsigned long gf2_matrix_times(mat, vec)
343 unsigned long *mat;
344 unsigned long vec;
345{
346 unsigned long sum;
347
348 sum = 0;
349 while (vec) {
350 if (vec & 1)
351 sum ^= *mat;
352 vec >>= 1;
353 mat++;
354 }
355 return sum;
356}
357
358/* ========================================================================= */
359local void gf2_matrix_square(square, mat)
360 unsigned long *square;
361 unsigned long *mat;
362{
363 int n;
364
365 for (n = 0; n < GF2_DIM; n++)
366 square[n] = gf2_matrix_times(mat, mat[n]);
367}
368
369/* ========================================================================= */
370uLong ZEXPORT crc32_combine(crc1, crc2, len2)
371 uLong crc1;
372 uLong crc2;
373 z_off_t len2;
374{
375 int n;
376 unsigned long row;
377 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
378 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
379
380 /* degenerate case */
381 if (len2 == 0)
382 return crc1;
383
384 /* put operator for one zero bit in odd */
385 odd[0] = 0xedb88320L; /* CRC-32 polynomial */
386 row = 1;
387 for (n = 1; n < GF2_DIM; n++) {
388 odd[n] = row;
389 row <<= 1;
390 }
391
392 /* put operator for two zero bits in even */
393 gf2_matrix_square(even, odd);
394
395 /* put operator for four zero bits in odd */
396 gf2_matrix_square(odd, even);
397
398 /* apply len2 zeros to crc1 (first square will put the operator for one
399 zero byte, eight zero bits, in even) */
400 do {
401 /* apply zeros operator for this bit of len2 */
402 gf2_matrix_square(even, odd);
403 if (len2 & 1)
404 crc1 = gf2_matrix_times(even, crc1);
405 len2 >>= 1;
406
407 /* if no more bits set, then done */
408 if (len2 == 0)
409 break;
410
411 /* another iteration of the loop with odd and even swapped */
412 gf2_matrix_square(odd, even);
413 if (len2 & 1)
414 crc1 = gf2_matrix_times(odd, crc1);
415 len2 >>= 1;
416
417 /* if no more bits set, then done */
418 } while (len2 != 0);
419
420 /* return combined crc */
421 crc1 ^= crc2;
422 return crc1;
423}