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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
35typedef 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
76local volatile int crc_table_empty = 1;
77local unsigned long FAR crc_table[TBLS][256];
78local 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*/
109local 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
186local 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 */
208const 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/* ========================================================================= */
222unsigned 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/* ========================================================================= */
265local 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/* ========================================================================= */
305local 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 */