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crc32.cc
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1 /* crc32.c -- compute the CRC-32 of a data stream
2  * Copyright (C) 1995-2006, 2010, 2011, 2012 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 in about a
9  * factor 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  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 /* Definitions for doing the crc four data bytes at a time. */
36 #if !defined(NOBYFOUR) && defined(Z_U4)
37 # define BYFOUR
38 #endif
39 #ifdef BYFOUR
40  local unsigned long crc32_little OF((unsigned long,
41  const unsigned char FAR *, unsigned));
42  local unsigned long crc32_big OF((unsigned long,
43  const unsigned char FAR *, unsigned));
44 # define TBLS 8
45 #else
46 # define TBLS 1
47 #endif /* BYFOUR */
48 
49 /* Local functions for crc concatenation */
50 local unsigned long gf2_matrix_times OF((unsigned long *mat,
51  unsigned long vec));
52 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
53 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
54 
55 
56 #ifdef DYNAMIC_CRC_TABLE
57 
58 local volatile int crc_table_empty = 1;
59 local z_crc_t FAR crc_table[TBLS][256];
60 local void make_crc_table OF((void));
61 #ifdef MAKECRCH
62  local void write_table OF((FILE *, const z_crc_t FAR *));
63 #endif /* MAKECRCH */
64 /*
65  Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
66  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.
67 
68  Polynomials over GF(2) are represented in binary, one bit per coefficient,
69  with the lowest powers in the most significant bit. Then adding polynomials
70  is just exclusive-or, and multiplying a polynomial by x is a right shift by
71  one. If we call the above polynomial p, and represent a byte as the
72  polynomial q, also with the lowest power in the most significant bit (so the
73  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
74  where a mod b means the remainder after dividing a by b.
75 
76  This calculation is done using the shift-register method of multiplying and
77  taking the remainder. The register is initialized to zero, and for each
78  incoming bit, x^32 is added mod p to the register if the bit is a one (where
79  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
80  x (which is shifting right by one and adding x^32 mod p if the bit shifted
81  out is a one). We start with the highest power (least significant bit) of
82  q and repeat for all eight bits of q.
83 
84  The first table is simply the CRC of all possible eight bit values. This is
85  all the information needed to generate CRCs on data a byte at a time for all
86  combinations of CRC register values and incoming bytes. The remaining tables
87  allow for word-at-a-time CRC calculation for both big-endian and little-
88  endian machines, where a word is four bytes.
89 */
90 local void make_crc_table()
91 {
92  z_crc_t c;
93  int n, k;
94  z_crc_t poly; /* polynomial exclusive-or pattern */
95  /* terms of polynomial defining this crc (except x^32): */
96  static volatile int first = 1; /* flag to limit concurrent making */
97  static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
98 
99  /* See if another task is already doing this (not thread-safe, but better
100  than nothing -- significantly reduces duration of vulnerability in
101  case the advice about DYNAMIC_CRC_TABLE is ignored) */
102  if (first) {
103  first = 0;
104 
105  /* make exclusive-or pattern from polynomial (0xedb88320UL) */
106  poly = 0;
107  for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
108  poly |= (z_crc_t)1 << (31 - p[n]);
109 
110  /* generate a crc for every 8-bit value */
111  for (n = 0; n < 256; n++) {
112  c = (z_crc_t)n;
113  for (k = 0; k < 8; k++)
114  c = c & 1 ? poly ^ (c >> 1) : c >> 1;
115  crc_table[0][n] = c;
116  }
117 
118 #ifdef BYFOUR
119  /* generate crc for each value followed by one, two, and three zeros,
120  and then the byte reversal of those as well as the first table */
121  for (n = 0; n < 256; n++) {
122  c = crc_table[0][n];
123  crc_table[4][n] = ZSWAP32(c);
124  for (k = 1; k < 4; k++) {
125  c = crc_table[0][c & 0xff] ^ (c >> 8);
126  crc_table[k][n] = c;
127  crc_table[k + 4][n] = ZSWAP32(c);
128  }
129  }
130 #endif /* BYFOUR */
131 
132  crc_table_empty = 0;
133  }
134  else { /* not first */
135  /* wait for the other guy to finish (not efficient, but rare) */
136  while (crc_table_empty)
137  ;
138  }
139 
140 #ifdef MAKECRCH
141  /* write out CRC tables to crc32.h */
142  {
143  FILE *out;
144 
145  out = fopen("crc32.h", "w");
146  if (out == NULL) return;
147  fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
148  fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
149  fprintf(out, "local const z_crc_t FAR ");
150  fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
151  write_table(out, crc_table[0]);
152 # ifdef BYFOUR
153  fprintf(out, "#ifdef BYFOUR\n");
154  for (k = 1; k < 8; k++) {
155  fprintf(out, " },\n {\n");
156  write_table(out, crc_table[k]);
157  }
158  fprintf(out, "#endif\n");
159 # endif /* BYFOUR */
160  fprintf(out, " }\n};\n");
161  fclose(out);
162  }
163 #endif /* MAKECRCH */
164 }
165 
166 #ifdef MAKECRCH
167 local void write_table(FILE *out,const z_crc_t FAR * table)
168 {
169  int n;
170 
171  for (n = 0; n < 256; n++)
172  fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
173  (unsigned long)(table[n]),
174  n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
175 }
176 #endif /* MAKECRCH */
177 
178 #else /* !DYNAMIC_CRC_TABLE */
179 /* ========================================================================
180  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
181  */
182 #include "crc32.h"
183 #endif /* DYNAMIC_CRC_TABLE */
184 
185 /* =========================================================================
186  * This function can be used by asm versions of crc32()
187  */
188 const z_crc_t FAR * ZEXPORT get_crc_table()
189 {
190 #ifdef DYNAMIC_CRC_TABLE
191  if (crc_table_empty)
192  make_crc_table();
193 #endif /* DYNAMIC_CRC_TABLE */
194  return (const z_crc_t FAR *)crc_table;
195 }
196 
197 /* ========================================================================= */
198 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
199 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
200 
201 /* ========================================================================= */
202 unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, uInt len)
203 {
204  if (buf == Z_NULL) return 0UL;
205 
206 #ifdef DYNAMIC_CRC_TABLE
207  if (crc_table_empty)
208  make_crc_table();
209 #endif /* DYNAMIC_CRC_TABLE */
210 
211 #ifdef BYFOUR
212  if (sizeof(void *) == sizeof(ptrdiff_t)) {
213  z_crc_t endian;
214 
215  endian = 1;
216  if (*((unsigned char *)(&endian)))
217  return crc32_little(crc, buf, len);
218  else
219  return crc32_big(crc, buf, len);
220  }
221 #endif /* BYFOUR */
222  crc = crc ^ 0xffffffffUL;
223  while (len >= 8) {
224  DO8;
225  len -= 8;
226  }
227  if (len) do {
228  DO1;
229  } while (--len);
230  return crc ^ 0xffffffffUL;
231 }
232 
233 #ifdef BYFOUR
234 
235 /* ========================================================================= */
236 #define DOLIT4 c ^= *buf4++; \
237  c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
238  crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
239 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
240 
241 /* ========================================================================= */
242 local unsigned long crc32_little(unsigned long crc, const unsigned char FAR *buf, unsigned len)
243 {
244  z_crc_t c;
245  const z_crc_t FAR *buf4;
246 
247  c = (z_crc_t)crc;
248  c = ~c;
249  while (len && ((ptrdiff_t)buf & 3)) {
250  c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
251  len--;
252  }
253 
254  buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
255  while (len >= 32) {
256  DOLIT32;
257  len -= 32;
258  }
259  while (len >= 4) {
260  DOLIT4;
261  len -= 4;
262  }
263  buf = (const unsigned char FAR *)buf4;
264 
265  if (len) do {
266  c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
267  } while (--len);
268  c = ~c;
269  return (unsigned long)c;
270 }
271 
272 /* ========================================================================= */
273 #define DOBIG4 c ^= *++buf4; \
274  c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
275  crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
276 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
277 
278 /* ========================================================================= */
279 local unsigned long crc32_big(unsigned long crc, const unsigned char FAR *buf, unsigned len)
280 {
281  z_crc_t c;
282  const z_crc_t FAR *buf4;
283 
284  c = ZSWAP32((z_crc_t)crc);
285  c = ~c;
286  while (len && ((ptrdiff_t)buf & 3)) {
287  c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
288  len--;
289  }
290 
291  buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
292  buf4--;
293  while (len >= 32) {
294  DOBIG32;
295  len -= 32;
296  }
297  while (len >= 4) {
298  DOBIG4;
299  len -= 4;
300  }
301  buf4++;
302  buf = (const unsigned char FAR *)buf4;
303 
304  if (len) do {
305  c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
306  } while (--len);
307  c = ~c;
308  return (unsigned long)(ZSWAP32(c));
309 }
310 
311 #endif /* BYFOUR */
312 
313 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
314 
315 /* ========================================================================= */
316 local unsigned long gf2_matrix_times(unsigned long *mat, unsigned long vec)
317 {
318  unsigned long sum;
319 
320  sum = 0;
321  while (vec) {
322  if (vec & 1)
323  sum ^= *mat;
324  vec >>= 1;
325  mat++;
326  }
327  return sum;
328 }
329 
330 /* ========================================================================= */
331 local void gf2_matrix_square(unsigned long *square, unsigned long *mat)
332 {
333  int n;
334 
335  for (n = 0; n < GF2_DIM; n++)
336  square[n] = gf2_matrix_times(mat, mat[n]);
337 }
338 
339 /* ========================================================================= */
340 local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2)
341 {
342  int n;
343  unsigned long row;
344  unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
345  unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
346 
347  /* degenerate case (also disallow negative lengths) */
348  if (len2 <= 0)
349  return crc1;
350 
351  /* put operator for one zero bit in odd */
352  odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
353  row = 1;
354  for (n = 1; n < GF2_DIM; n++) {
355  odd[n] = row;
356  row <<= 1;
357  }
358 
359  /* put operator for two zero bits in even */
360  gf2_matrix_square(even, odd);
361 
362  /* put operator for four zero bits in odd */
363  gf2_matrix_square(odd, even);
364 
365  /* apply len2 zeros to crc1 (first square will put the operator for one
366  zero byte, eight zero bits, in even) */
367  do {
368  /* apply zeros operator for this bit of len2 */
369  gf2_matrix_square(even, odd);
370  if (len2 & 1)
371  crc1 = gf2_matrix_times(even, crc1);
372  len2 >>= 1;
373 
374  /* if no more bits set, then done */
375  if (len2 == 0)
376  break;
377 
378  /* another iteration of the loop with odd and even swapped */
379  gf2_matrix_square(odd, even);
380  if (len2 & 1)
381  crc1 = gf2_matrix_times(odd, crc1);
382  len2 >>= 1;
383 
384  /* if no more bits set, then done */
385  } while (len2 != 0);
386 
387  /* return combined crc */
388  crc1 ^= crc2;
389  return crc1;
390 }
391 
392 /* ========================================================================= */
393 uLong ZEXPORT crc32_combine(uLong crc1, uLong crc2, z_off_t len2)
394 {
395  return crc32_combine_(crc1, crc2, len2);
396 }
397 
398 uLong ZEXPORT crc32_combine64(uLong crc1, uLong crc2, z_off64_t len2)
399 {
400  return crc32_combine_(crc1, crc2, len2);
401 }
const XML_Char int len
Definition: expat.h:262
unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, uInt len)
Definition: crc32.cc:202
local const z_crc_t FAR crc_table[TBLS][256]
Definition: crc32.h:5
const z_crc_t FAR *ZEXPORT get_crc_table()
Definition: crc32.cc:188
const char * p
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#define ZSWAP32(q)
Definition: zutil.h:250
local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.cc:340
#define GF2_DIM
Definition: crc32.cc:313
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local void gf2_matrix_square(unsigned long *square, unsigned long *mat)
Definition: crc32.cc:331
const G4int n
#define DO8
Definition: crc32.cc:199
uLong ZEXPORT crc32_combine(uLong crc1, uLong crc2, z_off_t len2)
Definition: crc32.cc:393
uLong ZEXPORT crc32_combine64(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.cc:398
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#define DO1
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#define local
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#define TBLS
Definition: crc32.cc:46
local unsigned long gf2_matrix_times(unsigned long *mat, unsigned long vec)
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