1 | /* |
2 | * Copyright (c) 2008-2016 Apple Inc. All rights reserved. |
3 | * |
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5 | * |
6 | * This file contains Original Code and/or Modifications of Original Code |
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8 | * Version 2.0 (the 'License'). You may not use this file except in |
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14 | * |
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17 | * |
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27 | */ |
28 | /* crc32.c -- compute the CRC-32 of a data stream |
29 | * Copyright (C) 1995-2005 Mark Adler |
30 | * For conditions of distribution and use, see copyright notice in zlib.h |
31 | * |
32 | * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster |
33 | * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing |
34 | * tables for updating the shift register in one step with three exclusive-ors |
35 | * instead of four steps with four exclusive-ors. This results in about a |
36 | * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. |
37 | */ |
38 | |
39 | /* @(#) $Id$ */ |
40 | |
41 | /* |
42 | Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore |
43 | protection on the static variables used to control the first-use generation |
44 | of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should |
45 | first call get_crc_table() to initialize the tables before allowing more than |
46 | one thread to use crc32(). |
47 | */ |
48 | |
49 | |
50 | #ifdef MAKECRCH |
51 | # include <stdio.h> |
52 | # ifndef DYNAMIC_CRC_TABLE |
53 | # define DYNAMIC_CRC_TABLE |
54 | # endif /* !DYNAMIC_CRC_TABLE */ |
55 | #endif /* MAKECRCH */ |
56 | |
57 | #include "zutil.h" /* for STDC and FAR definitions */ |
58 | |
59 | #define local static |
60 | |
61 | /* Find a four-byte integer type for crc32_little() and crc32_big(). */ |
62 | #ifndef NOBYFOUR |
63 | # ifdef STDC /* need ANSI C limits.h to determine sizes */ |
64 | # include <machine/limits.h> |
65 | # define BYFOUR |
66 | # if (UINT_MAX == 0xffffffffUL) |
67 | typedef unsigned int u4; |
68 | # else |
69 | # if (ULONG_MAX == 0xffffffffUL) |
70 | typedef unsigned long u4; |
71 | # else |
72 | # if (USHRT_MAX == 0xffffffffUL) |
73 | typedef unsigned short u4; |
74 | # else |
75 | # undef BYFOUR /* can't find a four-byte integer type! */ |
76 | # endif |
77 | # endif |
78 | # endif |
79 | # endif /* STDC */ |
80 | #endif /* !NOBYFOUR */ |
81 | |
82 | /* Definitions for doing the crc four data bytes at a time. */ |
83 | #ifdef BYFOUR |
84 | # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ |
85 | (((w)&0xff00)<<8)+(((w)&0xff)<<24)) |
86 | local unsigned long crc32_little OF((unsigned long, |
87 | const unsigned char FAR *, unsigned)); |
88 | local unsigned long crc32_big OF((unsigned long, |
89 | const unsigned char FAR *, unsigned)); |
90 | # define TBLS 8 |
91 | #else |
92 | # define TBLS 1 |
93 | #endif /* BYFOUR */ |
94 | |
95 | /* Local functions for crc concatenation */ |
96 | local unsigned long gf2_matrix_times OF((unsigned long *mat, |
97 | unsigned long vec)); |
98 | local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); |
99 | |
100 | #ifdef DYNAMIC_CRC_TABLE |
101 | |
102 | local volatile int crc_table_empty = 1; |
103 | local unsigned long FAR crc_table[TBLS][256]; |
104 | local void make_crc_table OF((void)); |
105 | #ifdef MAKECRCH |
106 | local void write_table OF((FILE *, const unsigned long FAR *)); |
107 | #endif /* MAKECRCH */ |
108 | /* |
109 | Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: |
110 | 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. |
111 | |
112 | Polynomials over GF(2) are represented in binary, one bit per coefficient, |
113 | with the lowest powers in the most significant bit. Then adding polynomials |
114 | is just exclusive-or, and multiplying a polynomial by x is a right shift by |
115 | one. If we call the above polynomial p, and represent a byte as the |
116 | polynomial q, also with the lowest power in the most significant bit (so the |
117 | byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, |
118 | where a mod b means the remainder after dividing a by b. |
119 | |
120 | This calculation is done using the shift-register method of multiplying and |
121 | taking the remainder. The register is initialized to zero, and for each |
122 | incoming bit, x^32 is added mod p to the register if the bit is a one (where |
123 | x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by |
124 | x (which is shifting right by one and adding x^32 mod p if the bit shifted |
125 | out is a one). We start with the highest power (least significant bit) of |
126 | q and repeat for all eight bits of q. |
127 | |
128 | The first table is simply the CRC of all possible eight bit values. This is |
129 | all the information needed to generate CRCs on data a byte at a time for all |
130 | combinations of CRC register values and incoming bytes. The remaining tables |
131 | allow for word-at-a-time CRC calculation for both big-endian and little- |
132 | endian machines, where a word is four bytes. |
133 | */ |
134 | local void |
135 | make_crc_table(void) |
136 | { |
137 | unsigned long c; |
138 | int n, k; |
139 | unsigned long poly; /* polynomial exclusive-or pattern */ |
140 | /* terms of polynomial defining this crc (except x^32): */ |
141 | static volatile int first = 1; /* flag to limit concurrent making */ |
142 | static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; |
143 | |
144 | /* See if another task is already doing this (not thread-safe, but better |
145 | than nothing -- significantly reduces duration of vulnerability in |
146 | case the advice about DYNAMIC_CRC_TABLE is ignored) */ |
147 | if (first) { |
148 | first = 0; |
149 | |
150 | /* make exclusive-or pattern from polynomial (0xedb88320UL) */ |
151 | poly = 0UL; |
152 | for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) |
153 | poly |= 1UL << (31 - p[n]); |
154 | |
155 | /* generate a crc for every 8-bit value */ |
156 | for (n = 0; n < 256; n++) { |
157 | c = (unsigned long)n; |
158 | for (k = 0; k < 8; k++) |
159 | c = c & 1 ? poly ^ (c >> 1) : c >> 1; |
160 | crc_table[0][n] = c; |
161 | } |
162 | |
163 | #ifdef BYFOUR |
164 | /* generate crc for each value followed by one, two, and three zeros, |
165 | and then the byte reversal of those as well as the first table */ |
166 | for (n = 0; n < 256; n++) { |
167 | c = crc_table[0][n]; |
168 | crc_table[4][n] = REV(c); |
169 | for (k = 1; k < 4; k++) { |
170 | c = crc_table[0][c & 0xff] ^ (c >> 8); |
171 | crc_table[k][n] = c; |
172 | crc_table[k + 4][n] = REV(c); |
173 | } |
174 | } |
175 | #endif /* BYFOUR */ |
176 | |
177 | crc_table_empty = 0; |
178 | } |
179 | else { /* not first */ |
180 | /* wait for the other guy to finish (not efficient, but rare) */ |
181 | while (crc_table_empty) |
182 | ; |
183 | } |
184 | |
185 | #ifdef MAKECRCH |
186 | /* write out CRC tables to crc32.h */ |
187 | { |
188 | FILE *out; |
189 | |
190 | out = fopen("crc32.h" , "w" ); |
191 | if (out == NULL) return; |
192 | fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n" ); |
193 | fprintf(out, " * Generated automatically by crc32.c\n */\n\n" ); |
194 | fprintf(out, "local const unsigned long FAR " ); |
195 | fprintf(out, "crc_table[TBLS][256] =\n{\n {\n" ); |
196 | write_table(out, crc_table[0]); |
197 | # ifdef BYFOUR |
198 | fprintf(out, "#ifdef BYFOUR\n" ); |
199 | for (k = 1; k < 8; k++) { |
200 | fprintf(out, " },\n {\n" ); |
201 | write_table(out, crc_table[k]); |
202 | } |
203 | fprintf(out, "#endif\n" ); |
204 | # endif /* BYFOUR */ |
205 | fprintf(out, " }\n};\n" ); |
206 | fclose(out); |
207 | } |
208 | #endif /* MAKECRCH */ |
209 | } |
210 | |
211 | #ifdef MAKECRCH |
212 | local void |
213 | write_table(FILE *out, const unsigned long FAR *table) |
214 | { |
215 | int n; |
216 | |
217 | for (n = 0; n < 256; n++) |
218 | fprintf(out, "%s0x%08lxUL%s" , n % 5 ? "" : " " , table[n], |
219 | n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", " )); |
220 | } |
221 | #endif /* MAKECRCH */ |
222 | |
223 | #else /* !DYNAMIC_CRC_TABLE */ |
224 | /* ======================================================================== |
225 | * Tables of CRC-32s of all single-byte values, made by make_crc_table(). |
226 | */ |
227 | #include "crc32.h" |
228 | #endif /* DYNAMIC_CRC_TABLE */ |
229 | |
230 | /* ========================================================================= |
231 | * This function can be used by asm versions of crc32() |
232 | */ |
233 | const unsigned long FAR * ZEXPORT |
234 | get_crc_table(void) |
235 | { |
236 | #ifdef DYNAMIC_CRC_TABLE |
237 | if (crc_table_empty) |
238 | make_crc_table(); |
239 | #endif /* DYNAMIC_CRC_TABLE */ |
240 | return (const unsigned long FAR *)crc_table; |
241 | } |
242 | |
243 | /* ========================================================================= */ |
244 | #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) |
245 | #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 |
246 | |
247 | /* ========================================================================= */ |
248 | unsigned long ZEXPORT |
249 | z_crc32(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
250 | { |
251 | if (buf == Z_NULL) return 0UL; |
252 | |
253 | #ifdef DYNAMIC_CRC_TABLE |
254 | if (crc_table_empty) |
255 | make_crc_table(); |
256 | #endif /* DYNAMIC_CRC_TABLE */ |
257 | |
258 | #ifdef BYFOUR |
259 | if (sizeof(void *) == sizeof(ptrdiff_t)) { |
260 | u4 endian; |
261 | |
262 | endian = 1; |
263 | if (*((unsigned char *)(&endian))) |
264 | return crc32_little(crc, buf, len); |
265 | else |
266 | return crc32_big(crc, buf, len); |
267 | } |
268 | #endif /* BYFOUR */ |
269 | crc = crc ^ 0xffffffffUL; |
270 | while (len >= 8) { |
271 | DO8; |
272 | len -= 8; |
273 | } |
274 | if (len) do { |
275 | DO1; |
276 | } while (--len); |
277 | return crc ^ 0xffffffffUL; |
278 | } |
279 | |
280 | #ifdef BYFOUR |
281 | |
282 | /* ========================================================================= */ |
283 | #define DOLIT4 c ^= *buf4++; \ |
284 | c = (u4)(crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ |
285 | crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]) |
286 | #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 |
287 | |
288 | /* ========================================================================= */ |
289 | local unsigned long |
290 | crc32_little(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
291 | { |
292 | u4 c; |
293 | const u4 FAR *buf4; |
294 | |
295 | c = (u4)crc; |
296 | c = ~c; |
297 | while (len && ((ptrdiff_t)buf & 3)) { |
298 | c = (u4)(crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8)); |
299 | len--; |
300 | } |
301 | |
302 | buf4 = (const u4 FAR *)(const void FAR *)buf; |
303 | while (len >= 32) { |
304 | DOLIT32; |
305 | len -= 32; |
306 | } |
307 | while (len >= 4) { |
308 | DOLIT4; |
309 | len -= 4; |
310 | } |
311 | buf = (const unsigned char FAR *)buf4; |
312 | |
313 | if (len) do { |
314 | c = (u4)(crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8)); |
315 | } while (--len); |
316 | c = ~c; |
317 | return (unsigned long)c; |
318 | } |
319 | |
320 | /* ========================================================================= */ |
321 | #define DOBIG4 c ^= *++buf4; \ |
322 | c = (u4)(crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ |
323 | crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]) |
324 | #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 |
325 | |
326 | /* ========================================================================= */ |
327 | local unsigned long |
328 | crc32_big(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
329 | { |
330 | u4 c; |
331 | const u4 FAR *buf4; |
332 | |
333 | c = REV((u4)crc); |
334 | c = ~c; |
335 | while (len && ((ptrdiff_t)buf & 3)) { |
336 | c = (u4)(crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8)); |
337 | len--; |
338 | } |
339 | |
340 | buf4 = (const u4 FAR *)(const void FAR *)buf; |
341 | buf4--; |
342 | while (len >= 32) { |
343 | DOBIG32; |
344 | len -= 32; |
345 | } |
346 | while (len >= 4) { |
347 | DOBIG4; |
348 | len -= 4; |
349 | } |
350 | buf4++; |
351 | buf = (const unsigned char FAR *)buf4; |
352 | |
353 | if (len) do { |
354 | c = (u4)(crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8)); |
355 | } while (--len); |
356 | c = ~c; |
357 | return (unsigned long)(REV(c)); |
358 | } |
359 | |
360 | #endif /* BYFOUR */ |
361 | |
362 | #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ |
363 | |
364 | /* ========================================================================= */ |
365 | local unsigned long |
366 | gf2_matrix_times(unsigned long *mat, unsigned long vec) |
367 | { |
368 | unsigned long sum; |
369 | |
370 | sum = 0; |
371 | while (vec) { |
372 | if (vec & 1) |
373 | sum ^= *mat; |
374 | vec >>= 1; |
375 | mat++; |
376 | } |
377 | return sum; |
378 | } |
379 | |
380 | /* ========================================================================= */ |
381 | local void |
382 | gf2_matrix_square(unsigned long *square, unsigned long *mat) |
383 | { |
384 | int n; |
385 | |
386 | for (n = 0; n < GF2_DIM; n++) |
387 | square[n] = gf2_matrix_times(mat, vec: mat[n]); |
388 | } |
389 | |
390 | /* ========================================================================= */ |
391 | uLong ZEXPORT |
392 | z_crc32_combine(uLong crc1, uLong crc2, z_off_t len2) |
393 | { |
394 | int n; |
395 | unsigned long row; |
396 | unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ |
397 | unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ |
398 | |
399 | /* degenerate case */ |
400 | if (len2 == 0) |
401 | return crc1; |
402 | |
403 | /* put operator for one zero bit in odd */ |
404 | odd[0] = 0xedb88320L; /* CRC-32 polynomial */ |
405 | row = 1; |
406 | for (n = 1; n < GF2_DIM; n++) { |
407 | odd[n] = row; |
408 | row <<= 1; |
409 | } |
410 | |
411 | /* put operator for two zero bits in even */ |
412 | gf2_matrix_square(square: even, mat: odd); |
413 | |
414 | /* put operator for four zero bits in odd */ |
415 | gf2_matrix_square(square: odd, mat: even); |
416 | |
417 | /* apply len2 zeros to crc1 (first square will put the operator for one |
418 | zero byte, eight zero bits, in even) */ |
419 | do { |
420 | /* apply zeros operator for this bit of len2 */ |
421 | gf2_matrix_square(square: even, mat: odd); |
422 | if (len2 & 1) |
423 | crc1 = gf2_matrix_times(mat: even, vec: crc1); |
424 | len2 >>= 1; |
425 | |
426 | /* if no more bits set, then done */ |
427 | if (len2 == 0) |
428 | break; |
429 | |
430 | /* another iteration of the loop with odd and even swapped */ |
431 | gf2_matrix_square(square: odd, mat: even); |
432 | if (len2 & 1) |
433 | crc1 = gf2_matrix_times(mat: odd, vec: crc1); |
434 | len2 >>= 1; |
435 | |
436 | /* if no more bits set, then done */ |
437 | } while (len2 != 0); |
438 | |
439 | /* return combined crc */ |
440 | crc1 ^= crc2; |
441 | return crc1; |
442 | } |
443 | |