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source: vbox/trunk/src/libs/zlib-1.2.6/crc32.c@ 51892

最後變更 在這個檔案從51892是 40354,由 vboxsync 提交於 13 年 前

libs/zlib-1.2.6: fix OSE
  • 屬性 svn:eol-style 設為 native
  • 屬性 svn:keywords 設為 Author Date Id Revision
檔案大小: 13.5 KB
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1/* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010, 2011 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 *
5 * Thanks to Rodney Brown <[email protected]> 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: crc32.c 40354 2012-03-05 13:39:00Z vboxsync $ */
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/* Find a four-byte integer type for crc32_little() and crc32_big(). */
36#ifndef NOBYFOUR
37# ifdef STDC /* need ANSI C limits.h to determine sizes */
38# include <limits.h>
39# define BYFOUR
40# if (UINT_MAX == 0xffffffffUL)
41 typedef unsigned int u4;
42# else
43# if (ULONG_MAX == 0xffffffffUL)
44 typedef unsigned long u4;
45# else
46# if (USHRT_MAX == 0xffffffffUL)
47 typedef unsigned short u4;
48# else
49# undef BYFOUR /* can't find a four-byte integer type! */
50# endif
51# endif
52# endif
53# endif /* STDC */
54#endif /* !NOBYFOUR */
55
56/* Definitions for doing the crc four data bytes at a time. */
57#ifdef BYFOUR
58 typedef u4 crc_table_t;
59# define REV(w) ((((w)>>24)&0xff)+(((w)>>8)&0xff00)+ \
60 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
61 local unsigned long crc32_little OF((unsigned long,
62 const unsigned char FAR *, unsigned));
63 local unsigned long crc32_big OF((unsigned long,
64 const unsigned char FAR *, unsigned));
65# define TBLS 8
66#else
67 typedef unsigned long crc_table_t;
68# define TBLS 1
69#endif /* BYFOUR */
70
71/* Local functions for crc concatenation */
72local unsigned long gf2_matrix_times OF((unsigned long *mat,
73 unsigned long vec));
74local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
75local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
76
77
78#ifdef DYNAMIC_CRC_TABLE
79
80local volatile int crc_table_empty = 1;
81local crc_table_t FAR crc_table[TBLS][256];
82local void make_crc_table OF((void));
83#ifdef MAKECRCH
84 local void write_table OF((FILE *, const crc_table_t FAR *));
85#endif /* MAKECRCH */
86/*
87 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
88 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.
89
90 Polynomials over GF(2) are represented in binary, one bit per coefficient,
91 with the lowest powers in the most significant bit. Then adding polynomials
92 is just exclusive-or, and multiplying a polynomial by x is a right shift by
93 one. If we call the above polynomial p, and represent a byte as the
94 polynomial q, also with the lowest power in the most significant bit (so the
95 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
96 where a mod b means the remainder after dividing a by b.
97
98 This calculation is done using the shift-register method of multiplying and
99 taking the remainder. The register is initialized to zero, and for each
100 incoming bit, x^32 is added mod p to the register if the bit is a one (where
101 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
102 x (which is shifting right by one and adding x^32 mod p if the bit shifted
103 out is a one). We start with the highest power (least significant bit) of
104 q and repeat for all eight bits of q.
105
106 The first table is simply the CRC of all possible eight bit values. This is
107 all the information needed to generate CRCs on data a byte at a time for all
108 combinations of CRC register values and incoming bytes. The remaining tables
109 allow for word-at-a-time CRC calculation for both big-endian and little-
110 endian machines, where a word is four bytes.
111*/
112local void make_crc_table()
113{
114 crc_table_t c;
115 int n, k;
116 crc_table_t poly; /* polynomial exclusive-or pattern */
117 /* terms of polynomial defining this crc (except x^32): */
118 static volatile int first = 1; /* flag to limit concurrent making */
119 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
120
121 /* See if another task is already doing this (not thread-safe, but better
122 than nothing -- significantly reduces duration of vulnerability in
123 case the advice about DYNAMIC_CRC_TABLE is ignored) */
124 if (first) {
125 first = 0;
126
127 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
128 poly = 0;
129 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
130 poly |= (crc_table_t)1 << (31 - p[n]);
131
132 /* generate a crc for every 8-bit value */
133 for (n = 0; n < 256; n++) {
134 c = (crc_table_t)n;
135 for (k = 0; k < 8; k++)
136 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
137 crc_table[0][n] = c;
138 }
139
140#ifdef BYFOUR
141 /* generate crc for each value followed by one, two, and three zeros,
142 and then the byte reversal of those as well as the first table */
143 for (n = 0; n < 256; n++) {
144 c = crc_table[0][n];
145 crc_table[4][n] = REV(c);
146 for (k = 1; k < 4; k++) {
147 c = crc_table[0][c & 0xff] ^ (c >> 8);
148 crc_table[k][n] = c;
149 crc_table[k + 4][n] = REV(c);
150 }
151 }
152#endif /* BYFOUR */
153
154 crc_table_empty = 0;
155 }
156 else { /* not first */
157 /* wait for the other guy to finish (not efficient, but rare) */
158 while (crc_table_empty)
159 ;
160 }
161
162#ifdef MAKECRCH
163 /* write out CRC tables to crc32.h */
164 {
165 FILE *out;
166
167 out = fopen("crc32.h", "w");
168 if (out == NULL) return;
169 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
170 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
171 fprintf(out, "local const crc_table_t FAR ");
172 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
173 write_table(out, crc_table[0]);
174# ifdef BYFOUR
175 fprintf(out, "#ifdef BYFOUR\n");
176 for (k = 1; k < 8; k++) {
177 fprintf(out, " },\n {\n");
178 write_table(out, crc_table[k]);
179 }
180 fprintf(out, "#endif\n");
181# endif /* BYFOUR */
182 fprintf(out, " }\n};\n");
183 fclose(out);
184 }
185#endif /* MAKECRCH */
186}
187
188#ifdef MAKECRCH
189local void write_table(out, table)
190 FILE *out;
191 const crc_table_t FAR *table;
192{
193 int n;
194
195 for (n = 0; n < 256; n++)
196 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
197 (unsigned long)(table[n]),
198 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
199}
200#endif /* MAKECRCH */
201
202#else /* !DYNAMIC_CRC_TABLE */
203/* ========================================================================
204 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
205 */
206#include "crc32.h"
207#endif /* DYNAMIC_CRC_TABLE */
208
209/* =========================================================================
210 * This function can be used by asm versions of crc32()
211 */
212const unsigned long FAR * ZEXPORT get_crc_table()
213{
214#ifdef DYNAMIC_CRC_TABLE
215 if (crc_table_empty)
216 make_crc_table();
217#endif /* DYNAMIC_CRC_TABLE */
218 return (const unsigned long FAR *)crc_table;
219}
220
221/* ========================================================================= */
222#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
223#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
224
225/* ========================================================================= */
226unsigned long ZEXPORT crc32(crc, buf, len)
227 unsigned long crc;
228 const unsigned char FAR *buf;
229 uInt len;
230{
231 if (buf == Z_NULL) return 0UL;
232
233#ifdef DYNAMIC_CRC_TABLE
234 if (crc_table_empty)
235 make_crc_table();
236#endif /* DYNAMIC_CRC_TABLE */
237
238#ifdef BYFOUR
239 if (sizeof(void *) == sizeof(ptrdiff_t)) {
240 u4 endian;
241
242 endian = 1;
243 if (*((unsigned char *)(&endian)))
244 return crc32_little(crc, buf, len);
245 else
246 return crc32_big(crc, buf, len);
247 }
248#endif /* BYFOUR */
249 crc = crc ^ 0xffffffffUL;
250 while (len >= 8) {
251 DO8;
252 len -= 8;
253 }
254 if (len) do {
255 DO1;
256 } while (--len);
257 return crc ^ 0xffffffffUL;
258}
259
260#ifdef BYFOUR
261
262/* ========================================================================= */
263#define DOLIT4 c ^= *buf4++; \
264 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
265 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
266#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
267
268/* ========================================================================= */
269local unsigned long crc32_little(crc, buf, len)
270 unsigned long crc;
271 const unsigned char FAR *buf;
272 unsigned len;
273{
274 register u4 c;
275 register const u4 FAR *buf4;
276
277 c = (u4)crc;
278 c = ~c;
279 while (len && ((ptrdiff_t)buf & 3)) {
280 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
281 len--;
282 }
283
284 buf4 = (const u4 FAR *)(const void FAR *)buf;
285 while (len >= 32) {
286 DOLIT32;
287 len -= 32;
288 }
289 while (len >= 4) {
290 DOLIT4;
291 len -= 4;
292 }
293 buf = (const unsigned char FAR *)buf4;
294
295 if (len) do {
296 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
297 } while (--len);
298 c = ~c;
299 return (unsigned long)c;
300}
301
302/* ========================================================================= */
303#define DOBIG4 c ^= *++buf4; \
304 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
305 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
306#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
307
308/* ========================================================================= */
309local unsigned long crc32_big(crc, buf, len)
310 unsigned long crc;
311 const unsigned char FAR *buf;
312 unsigned len;
313{
314 register u4 c;
315 register const u4 FAR *buf4;
316
317 c = REV((u4)crc);
318 c = ~c;
319 while (len && ((ptrdiff_t)buf & 3)) {
320 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
321 len--;
322 }
323
324 buf4 = (const u4 FAR *)(const void FAR *)buf;
325 buf4--;
326 while (len >= 32) {
327 DOBIG32;
328 len -= 32;
329 }
330 while (len >= 4) {
331 DOBIG4;
332 len -= 4;
333 }
334 buf4++;
335 buf = (const unsigned char FAR *)buf4;
336
337 if (len) do {
338 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
339 } while (--len);
340 c = ~c;
341 return (unsigned long)(REV(c));
342}
343
344#endif /* BYFOUR */
345
346#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
347
348/* ========================================================================= */
349local unsigned long gf2_matrix_times(mat, vec)
350 unsigned long *mat;
351 unsigned long vec;
352{
353 unsigned long sum;
354
355 sum = 0;
356 while (vec) {
357 if (vec & 1)
358 sum ^= *mat;
359 vec >>= 1;
360 mat++;
361 }
362 return sum;
363}
364
365/* ========================================================================= */
366local void gf2_matrix_square(square, mat)
367 unsigned long *square;
368 unsigned long *mat;
369{
370 int n;
371
372 for (n = 0; n < GF2_DIM; n++)
373 square[n] = gf2_matrix_times(mat, mat[n]);
374}
375
376/* ========================================================================= */
377local uLong crc32_combine_(crc1, crc2, len2)
378 uLong crc1;
379 uLong crc2;
380 z_off64_t len2;
381{
382 int n;
383 unsigned long row;
384 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
385 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
386
387 /* degenerate case (also disallow negative lengths) */
388 if (len2 <= 0)
389 return crc1;
390
391 /* put operator for one zero bit in odd */
392 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
393 row = 1;
394 for (n = 1; n < GF2_DIM; n++) {
395 odd[n] = row;
396 row <<= 1;
397 }
398
399 /* put operator for two zero bits in even */
400 gf2_matrix_square(even, odd);
401
402 /* put operator for four zero bits in odd */
403 gf2_matrix_square(odd, even);
404
405 /* apply len2 zeros to crc1 (first square will put the operator for one
406 zero byte, eight zero bits, in even) */
407 do {
408 /* apply zeros operator for this bit of len2 */
409 gf2_matrix_square(even, odd);
410 if (len2 & 1)
411 crc1 = gf2_matrix_times(even, crc1);
412 len2 >>= 1;
413
414 /* if no more bits set, then done */
415 if (len2 == 0)
416 break;
417
418 /* another iteration of the loop with odd and even swapped */
419 gf2_matrix_square(odd, even);
420 if (len2 & 1)
421 crc1 = gf2_matrix_times(odd, crc1);
422 len2 >>= 1;
423
424 /* if no more bits set, then done */
425 } while (len2 != 0);
426
427 /* return combined crc */
428 crc1 ^= crc2;
429 return crc1;
430}
431
432/* ========================================================================= */
433uLong ZEXPORT crc32_combine(crc1, crc2, len2)
434 uLong crc1;
435 uLong crc2;
436 z_off_t len2;
437{
438 return crc32_combine_(crc1, crc2, len2);
439}
440
441uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
442 uLong crc1;
443 uLong crc2;
444 z_off64_t len2;
445{
446 return crc32_combine_(crc1, crc2, len2);
447}
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