1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010 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 /* \param (#) $Id$ */
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
31 #define local static
32
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)&0xff)+(((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
67 /* Local functions for crc concatenation */
68 local unsigned long gf2_matrix_times OF((unsigned long *mat,
69 unsigned long vec));
70 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
71 local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2);
72
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 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
84 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.
85
86 Polynomials over GF(2) are represented in binary, one bit per coefficient,
87 with the lowest powers in the most significant bit. Then adding polynomials
88 is just exclusive-or, and multiplying a polynomial by x is a right shift by
89 one. If we call the above polynomial p, and represent a byte as the
90 polynomial q, also with the lowest power in the most significant bit (so the
91 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
92 where a mod b means the remainder after dividing a by b.
93
94 This calculation is done using the shift-register method of multiplying and
95 taking the remainder. The register is initialized to zero, and for each
96 incoming bit, x^32 is added mod p to the register if the bit is a one (where
97 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
98 x (which is shifting right by one and adding x^32 mod p if the bit shifted
99 out is a one). We start with the highest power (least significant bit) of
100 q and repeat for all eight bits of q.
101
102 The first table is simply the CRC of all possible eight bit values. This is
103 all the information needed to generate CRCs on data a byte at a time for all
104 combinations of CRC register values and incoming bytes. The remaining tables
105 allow for word-at-a-time CRC calculation for both big-endian and little-
106 endian machines, where a word is four bytes.
107 */
make_crc_table()108 local void make_crc_table()
109 {
110 unsigned long c;
111 int n, k;
112 unsigned long poly; /* polynomial exclusive-or pattern */
113 /* terms of polynomial defining this crc (except x^32): */
114 static volatile int first = 1; /* flag to limit concurrent making */
115 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
116
117 /* See if another task is already doing this (not thread-safe, but better
118 than nothing -- significantly reduces duration of vulnerability in
119 case the advice about DYNAMIC_CRC_TABLE is ignored) */
120 if (first) {
121 first = 0;
122
123 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
124 poly = 0UL;
125 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
126 poly |= 1UL << (31 - p[n]);
127
128 /* generate a crc for every 8-bit value */
129 for (n = 0; n < 256; n++) {
130 c = (unsigned long)n;
131 for (k = 0; k < 8; k++)
132 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
133 crc_table[0][n] = c;
134 }
135
136 #ifdef BYFOUR
137 /* generate crc for each value followed by one, two, and three zeros,
138 and then the byte reversal of those as well as the first table */
139 for (n = 0; n < 256; n++) {
140 c = crc_table[0][n];
141 crc_table[4][n] = REV(c);
142 for (k = 1; k < 4; k++) {
143 c = crc_table[0][c & 0xff] ^ (c >> 8);
144 crc_table[k][n] = c;
145 crc_table[k + 4][n] = REV(c);
146 }
147 }
148 #endif /* BYFOUR */
149
150 crc_table_empty = 0;
151 }
152 else { /* not first */
153 /* wait for the other guy to finish (not efficient, but rare) */
154 while (crc_table_empty)
155 ;
156 }
157
158 #ifdef MAKECRCH
159 /* write out CRC tables to crc32.h */
160 {
161 FILE *out;
162
163 out = fopen("crc32.h", "w");
164 if (out == NULL) return;
165 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
166 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
167 fprintf(out, "local const unsigned long FAR ");
168 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
169 write_table(out, crc_table[0]);
170 # ifdef BYFOUR
171 fprintf(out, "#ifdef BYFOUR\n");
172 for (k = 1; k < 8; k++) {
173 fprintf(out, " },\n {\n");
174 write_table(out, crc_table[k]);
175 }
176 fprintf(out, "#endif\n");
177 # endif /* BYFOUR */
178 fprintf(out, " }\n};\n");
179 fclose(out);
180 }
181 #endif /* MAKECRCH */
182 }
183
184 #ifdef MAKECRCH
write_table(out,table)185 local void write_table(out, table)
186 FILE *out;
187 const unsigned long FAR *table;
188 {
189 int n;
190
191 for (n = 0; n < 256; n++)
192 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
193 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
194 }
195 #endif /* MAKECRCH */
196
197 #else /* !DYNAMIC_CRC_TABLE */
198 /* ========================================================================
199 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
200 */
201 #include "crc32.h"
202 #endif /* DYNAMIC_CRC_TABLE */
203
204 /* =========================================================================
205 * This function can be used by asm versions of crc32()
206 */
get_crc_table()207 const unsigned long FAR * ZEXPORT get_crc_table()
208 {
209 #ifdef DYNAMIC_CRC_TABLE
210 if (crc_table_empty)
211 make_crc_table();
212 #endif /* DYNAMIC_CRC_TABLE */
213 return (const unsigned long FAR *)crc_table;
214 }
215
216 /* ========================================================================= */
217 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
218 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
219
220 /* ========================================================================= */
crc32(crc,buf,len)221 unsigned long ZEXPORT crc32(crc, buf, len)
222 unsigned long crc;
223 const unsigned char FAR *buf;
224 uInt len;
225 {
226 if (buf == Z_NULL) return 0UL;
227
228 #ifdef DYNAMIC_CRC_TABLE
229 if (crc_table_empty)
230 make_crc_table();
231 #endif /* DYNAMIC_CRC_TABLE */
232
233 #ifdef BYFOUR
234 if (sizeof(void *) == sizeof(ptrdiff_t)) {
235 u4 endian;
236
237 endian = 1;
238 if (*((unsigned char *)(&endian)))
239 return crc32_little(crc, buf, len);
240 else
241 return crc32_big(crc, buf, len);
242 }
243 #endif /* BYFOUR */
244 crc = crc ^ 0xffffffffUL;
245 while (len >= 8) {
246 DO8;
247 len -= 8;
248 }
249 if (len) do {
250 DO1;
251 } while (--len);
252 return crc ^ 0xffffffffUL;
253 }
254
255 #ifdef BYFOUR
256
257 /* ========================================================================= */
258 #define DOLIT4 c ^= *buf4++; \
259 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
260 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
261 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
262
263 /* ========================================================================= */
crc32_little(crc,buf,len)264 local unsigned long crc32_little(crc, buf, len)
265 unsigned long crc;
266 const unsigned char FAR *buf;
267 unsigned len;
268 {
269 register u4 c;
270 register const u4 FAR *buf4;
271
272 c = (u4)crc;
273 c = ~c;
274 while (len && ((ptrdiff_t)buf & 3)) {
275 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
276 len--;
277 }
278
279 buf4 = (const u4 FAR *)(const void FAR *)buf;
280 while (len >= 32) {
281 DOLIT32;
282 len -= 32;
283 }
284 while (len >= 4) {
285 DOLIT4;
286 len -= 4;
287 }
288 buf = (const unsigned char FAR *)buf4;
289
290 if (len) do {
291 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
292 } while (--len);
293 c = ~c;
294 return (unsigned long)c;
295 }
296
297 /* ========================================================================= */
298 #define DOBIG4 c ^= *buf4++; \
299 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
300 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
301 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
302
303 /* ========================================================================= */
crc32_big(crc,buf,len)304 local unsigned long crc32_big(crc, buf, len)
305 unsigned long crc;
306 const unsigned char FAR *buf;
307 unsigned len;
308 {
309 register u4 c;
310 register const u4 FAR *buf4;
311
312 c = REV((u4)crc);
313 c = ~c;
314 while (len && ((ptrdiff_t)buf & 3)) {
315 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
316 len--;
317 }
318
319 buf4 = (const u4 FAR *)(const void FAR *)buf;
320 while (len >= 32) {
321 DOBIG32;
322 len -= 32;
323 }
324 while (len >= 4) {
325 DOBIG4;
326 len -= 4;
327 }
328 buf = (const unsigned char FAR *)buf4;
329
330 if (len) do {
331 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
332 } while (--len);
333 c = ~c;
334 return (unsigned long)(REV(c));
335 }
336
337 #endif /* BYFOUR */
338
339 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
340
341 /* ========================================================================= */
gf2_matrix_times(mat,vec)342 local 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 /* ========================================================================= */
gf2_matrix_square(square,mat)359 local 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 /* ========================================================================= */
crc32_combine_(crc1,crc2,len2)370 local uLong crc32_combine_(crc1, crc2, len2)
371 uLong crc1;
372 uLong crc2;
373 z_off64_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 (also disallow negative lengths) */
381 if (len2 <= 0)
382 return crc1;
383
384 /* put operator for one zero bit in odd */
385 odd[0] = 0xedb88320UL; /* 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 }
424
425 /* ========================================================================= */
crc32_combine(crc1,crc2,len2)426 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
427 uLong crc1;
428 uLong crc2;
429 z_off_t len2;
430 {
431 return crc32_combine_(crc1, crc2, len2);
432 }
433
crc32_combine64(crc1,crc2,len2)434 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
435 uLong crc1;
436 uLong crc2;
437 z_off64_t len2;
438 {
439 return crc32_combine_(crc1, crc2, len2);
440 }
441