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1 | /* crc32.c -- compute the CRC-32 of a data stream |
2 | * Copyright (C) 1995-2003 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 about a factor | |
9 | * 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 | #define STDC | |
31 | #define FAR | |
32 | #define Z_NULL ((void*)0) | |
33 | #define OF(X) X | |
34 | #define ZEXPORT | |
35 | typedef long ptrdiff_t; | |
36 | #define NOBYFOUR | |
37 | ||
38 | #define local static | |
39 | ||
40 | /* Find a four-byte integer type for crc32_little() and crc32_big(). */ | |
41 | #ifndef NOBYFOUR | |
42 | # ifdef STDC /* need ANSI C limits.h to determine sizes */ | |
43 | # include <limits.h> | |
44 | # define BYFOUR | |
45 | # if (UINT_MAX == 0xffffffffUL) | |
46 | typedef unsigned int u4; | |
47 | # else | |
48 | # if (ULONG_MAX == 0xffffffffUL) | |
49 | typedef unsigned long u4; | |
50 | # else | |
51 | # if (USHRT_MAX == 0xffffffffUL) | |
52 | typedef unsigned short u4; | |
53 | # else | |
54 | # undef BYFOUR /* can't find a four-byte integer type! */ | |
55 | # endif | |
56 | # endif | |
57 | # endif | |
58 | # endif /* STDC */ | |
59 | #endif /* !NOBYFOUR */ | |
60 | ||
61 | /* Definitions for doing the crc four data bytes at a time. */ | |
62 | #ifdef BYFOUR | |
63 | # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ | |
64 | (((w)&0xff00)<<8)+(((w)&0xff)<<24)) | |
65 | local unsigned long crc32_little OF((unsigned long, | |
66 | const unsigned char FAR *, unsigned)); | |
67 | local unsigned long crc32_big OF((unsigned long, | |
68 | const unsigned char FAR *, unsigned)); | |
69 | # define TBLS 8 | |
70 | #else | |
71 | # define TBLS 1 | |
72 | #endif /* BYFOUR */ | |
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 | /* | |
84 | Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: | |
85 | 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. | |
86 | ||
87 | Polynomials over GF(2) are represented in binary, one bit per coefficient, | |
88 | with the lowest powers in the most significant bit. Then adding polynomials | |
89 | is just exclusive-or, and multiplying a polynomial by x is a right shift by | |
90 | one. If we call the above polynomial p, and represent a byte as the | |
91 | polynomial q, also with the lowest power in the most significant bit (so the | |
92 | byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, | |
93 | where a mod b means the remainder after dividing a by b. | |
94 | ||
95 | This calculation is done using the shift-register method of multiplying and | |
96 | taking the remainder. The register is initialized to zero, and for each | |
97 | incoming bit, x^32 is added mod p to the register if the bit is a one (where | |
98 | x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by | |
99 | x (which is shifting right by one and adding x^32 mod p if the bit shifted | |
100 | out is a one). We start with the highest power (least significant bit) of | |
101 | q and repeat for all eight bits of q. | |
102 | ||
103 | The first table is simply the CRC of all possible eight bit values. This is | |
104 | all the information needed to generate CRCs on data a byte at a time for all | |
105 | combinations of CRC register values and incoming bytes. The remaining tables | |
106 | allow for word-at-a-time CRC calculation for both big-endian and little- | |
107 | endian machines, where a word is four bytes. | |
108 | */ | |
109 | local void make_crc_table() | |
110 | { | |
111 | unsigned long c; | |
112 | int n, k; | |
113 | unsigned long poly; /* polynomial exclusive-or pattern */ | |
114 | /* terms of polynomial defining this crc (except x^32): */ | |
115 | static volatile int first = 1; /* flag to limit concurrent making */ | |
116 | static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; | |
117 | ||
118 | /* See if another task is already doing this (not thread-safe, but better | |
119 | than nothing -- significantly reduces duration of vulnerability in | |
120 | case the advice about DYNAMIC_CRC_TABLE is ignored) */ | |
121 | if (first) { | |
122 | first = 0; | |
123 | ||
124 | /* make exclusive-or pattern from polynomial (0xedb88320UL) */ | |
125 | poly = 0UL; | |
126 | for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) | |
127 | poly |= 1UL << (31 - p[n]); | |
128 | ||
129 | /* generate a crc for every 8-bit value */ | |
130 | for (n = 0; n < 256; n++) { | |
131 | c = (unsigned long)n; | |
132 | for (k = 0; k < 8; k++) | |
133 | c = c & 1 ? poly ^ (c >> 1) : c >> 1; | |
134 | crc_table[0][n] = c; | |
135 | } | |
136 | ||
137 | #ifdef BYFOUR | |
138 | /* generate crc for each value followed by one, two, and three zeros, | |
139 | and then the byte reversal of those as well as the first table */ | |
140 | for (n = 0; n < 256; n++) { | |
141 | c = crc_table[0][n]; | |
142 | crc_table[4][n] = REV(c); | |
143 | for (k = 1; k < 4; k++) { | |
144 | c = crc_table[0][c & 0xff] ^ (c >> 8); | |
145 | crc_table[k][n] = c; | |
146 | crc_table[k + 4][n] = REV(c); | |
147 | } | |
148 | } | |
149 | #endif /* BYFOUR */ | |
150 | ||
151 | crc_table_empty = 0; | |
152 | } | |
153 | else { /* not first */ | |
154 | /* wait for the other guy to finish (not efficient, but rare) */ | |
155 | while (crc_table_empty) | |
156 | ; | |
157 | } | |
158 | ||
159 | #ifdef MAKECRCH | |
160 | /* write out CRC tables to crc32.h */ | |
161 | { | |
162 | FILE *out; | |
163 | ||
164 | out = fopen("crc32.h", "w"); | |
165 | if (out == NULL) return; | |
166 | fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); | |
167 | fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); | |
168 | fprintf(out, "local const unsigned long FAR "); | |
169 | fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); | |
170 | write_table(out, crc_table[0]); | |
171 | # ifdef BYFOUR | |
172 | fprintf(out, "#ifdef BYFOUR\n"); | |
173 | for (k = 1; k < 8; k++) { | |
174 | fprintf(out, " },\n {\n"); | |
175 | write_table(out, crc_table[k]); | |
176 | } | |
177 | fprintf(out, "#endif\n"); | |
178 | # endif /* BYFOUR */ | |
179 | fprintf(out, " }\n};\n"); | |
180 | fclose(out); | |
181 | } | |
182 | #endif /* MAKECRCH */ | |
183 | } | |
184 | ||
185 | #ifdef MAKECRCH | |
186 | local void write_table(out, table) | |
187 | FILE *out; | |
188 | const unsigned long FAR *table; | |
189 | { | |
190 | int n; | |
191 | ||
192 | for (n = 0; n < 256; n++) | |
193 | fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n], | |
194 | n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); | |
195 | } | |
196 | #endif /* MAKECRCH */ | |
197 | ||
198 | #else /* !DYNAMIC_CRC_TABLE */ | |
199 | /* ======================================================================== | |
200 | * Tables of CRC-32s of all single-byte values, made by make_crc_table(). | |
201 | */ | |
202 | #include "crc32.h" | |
203 | #endif /* DYNAMIC_CRC_TABLE */ | |
204 | ||
205 | /* ========================================================================= | |
206 | * This function can be used by asm versions of crc32() | |
207 | */ | |
208 | const unsigned long FAR * ZEXPORT get_crc_table(void) | |
209 | { | |
210 | #ifdef DYNAMIC_CRC_TABLE | |
211 | if (crc_table_empty) | |
212 | make_crc_table(); | |
213 | #endif /* DYNAMIC_CRC_TABLE */ | |
214 | return (const unsigned long FAR *)crc_table; | |
215 | } | |
216 | ||
217 | /* ========================================================================= */ | |
218 | #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) | |
219 | #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 | |
220 | ||
221 | /* ========================================================================= */ | |
222 | unsigned long ZEXPORT crc32( | |
223 | unsigned long crc, | |
224 | const unsigned char FAR *buf, | |
225 | unsigned len) | |
226 | { | |
227 | if (buf == Z_NULL) return 0UL; | |
228 | ||
229 | #ifdef DYNAMIC_CRC_TABLE | |
230 | if (crc_table_empty) | |
231 | make_crc_table(); | |
232 | #endif /* DYNAMIC_CRC_TABLE */ | |
233 | ||
234 | #ifdef BYFOUR | |
235 | if (sizeof(void *) == sizeof(ptrdiff_t)) { | |
236 | u4 endian; | |
237 | ||
238 | endian = 1; | |
239 | if (*((unsigned char *)(&endian))) | |
240 | return crc32_little(crc, buf, len); | |
241 | else | |
242 | return crc32_big(crc, buf, len); | |
243 | } | |
244 | #endif /* BYFOUR */ | |
245 | /* crc = crc ^ 0xffffffffUL;*/ | |
246 | while (len >= 8) { | |
247 | DO8; | |
248 | len -= 8; | |
249 | } | |
250 | if (len) do { | |
251 | DO1; | |
252 | } while (--len); | |
253 | return crc /* ^ 0xffffffffUL*/; | |
254 | } | |
255 | ||
256 | #ifdef BYFOUR | |
257 | ||
258 | /* ========================================================================= */ | |
259 | #define DOLIT4 c ^= *buf4++; \ | |
260 | c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ | |
261 | crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] | |
262 | #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 | |
263 | ||
264 | /* ========================================================================= */ | |
265 | local unsigned long crc32_little(crc, buf, len) | |
266 | unsigned long crc; | |
267 | const unsigned char FAR *buf; | |
268 | unsigned len; | |
269 | { | |
270 | register u4 c; | |
271 | register const u4 FAR *buf4; | |
272 | ||
273 | c = (u4)crc; | |
274 | c = ~c; | |
275 | while (len && ((ptrdiff_t)buf & 3)) { | |
276 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); | |
277 | len--; | |
278 | } | |
279 | ||
280 | buf4 = (const u4 FAR *)buf; | |
281 | while (len >= 32) { | |
282 | DOLIT32; | |
283 | len -= 32; | |
284 | } | |
285 | while (len >= 4) { | |
286 | DOLIT4; | |
287 | len -= 4; | |
288 | } | |
289 | buf = (const unsigned char FAR *)buf4; | |
290 | ||
291 | if (len) do { | |
292 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); | |
293 | } while (--len); | |
294 | c = ~c; | |
295 | return (unsigned long)c; | |
296 | } | |
297 | ||
298 | /* ========================================================================= */ | |
299 | #define DOBIG4 c ^= *++buf4; \ | |
300 | c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ | |
301 | crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] | |
302 | #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 | |
303 | ||
304 | /* ========================================================================= */ | |
305 | local unsigned long crc32_big(crc, buf, len) | |
306 | unsigned long crc; | |
307 | const unsigned char FAR *buf; | |
308 | unsigned len; | |
309 | { | |
310 | register u4 c; | |
311 | register const u4 FAR *buf4; | |
312 | ||
313 | c = REV((u4)crc); | |
314 | c = ~c; | |
315 | while (len && ((ptrdiff_t)buf & 3)) { | |
316 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); | |
317 | len--; | |
318 | } | |
319 | ||
320 | buf4 = (const u4 FAR *)buf; | |
321 | buf4--; | |
322 | while (len >= 32) { | |
323 | DOBIG32; | |
324 | len -= 32; | |
325 | } | |
326 | while (len >= 4) { | |
327 | DOBIG4; | |
328 | len -= 4; | |
329 | } | |
330 | buf4++; | |
331 | buf = (const unsigned char FAR *)buf4; | |
332 | ||
333 | if (len) do { | |
334 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); | |
335 | } while (--len); | |
336 | c = ~c; | |
337 | return (unsigned long)(REV(c)); | |
338 | } | |
339 | ||
340 | #endif /* BYFOUR */ |