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crc32.c
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1 /* crc32.c -- compute the CRC-32 of a data stream
2  * Copyright (C) 1995-2006, 2010, 2011, 2012, 2016 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 /* Definitions for doing the crc four data bytes at a time. */
34 #if !defined(NOBYFOUR) && defined(Z_U4)
35 # define BYFOUR
36 #endif
37 #ifdef BYFOUR
38  local unsigned long crc32_little OF((unsigned long,
39  const unsigned char FAR *, z_size_t));
40  local unsigned long crc32_big OF((unsigned long,
41  const unsigned char FAR *, z_size_t));
42 # define TBLS 8
43 #else
44 # define TBLS 1
45 #endif /* BYFOUR */
46 
47 /* Local functions for crc concatenation */
48 local unsigned long gf2_matrix_times OF((unsigned long *mat,
49  unsigned long vec));
50 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
51 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
52 
53 
54 #ifdef DYNAMIC_CRC_TABLE
55 
56 local volatile int crc_table_empty = 1;
58 local void make_crc_table OF((void));
59 #ifdef MAKECRCH
60  local void write_table OF((FILE *, const z_crc_t FAR *));
61 #endif /* MAKECRCH */
62 /*
63  Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
64  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.
65 
66  Polynomials over GF(2) are represented in binary, one bit per coefficient,
67  with the lowest powers in the most significant bit. Then adding polynomials
68  is just exclusive-or, and multiplying a polynomial by x is a right shift by
69  one. If we call the above polynomial p, and represent a byte as the
70  polynomial q, also with the lowest power in the most significant bit (so the
71  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
72  where a mod b means the remainder after dividing a by b.
73 
74  This calculation is done using the shift-register method of multiplying and
75  taking the remainder. The register is initialized to zero, and for each
76  incoming bit, x^32 is added mod p to the register if the bit is a one (where
77  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
78  x (which is shifting right by one and adding x^32 mod p if the bit shifted
79  out is a one). We start with the highest power (least significant bit) of
80  q and repeat for all eight bits of q.
81 
82  The first table is simply the CRC of all possible eight bit values. This is
83  all the information needed to generate CRCs on data a byte at a time for all
84  combinations of CRC register values and incoming bytes. The remaining tables
85  allow for word-at-a-time CRC calculation for both big-endian and little-
86  endian machines, where a word is four bytes.
87 */
88 local void make_crc_table()
89 {
90  z_crc_t c;
91  int n, k;
92  z_crc_t poly; /* polynomial exclusive-or pattern */
93  /* terms of polynomial defining this crc (except x^32): */
94  static volatile int first = 1; /* flag to limit concurrent making */
95  static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
96 
97  /* See if another task is already doing this (not thread-safe, but better
98  than nothing -- significantly reduces duration of vulnerability in
99  case the advice about DYNAMIC_CRC_TABLE is ignored) */
100  if (first) {
101  first = 0;
102 
103  /* make exclusive-or pattern from polynomial (0xedb88320UL) */
104  poly = 0;
105  for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
106  poly |= (z_crc_t)1 << (31 - p[n]);
107 
108  /* generate a crc for every 8-bit value */
109  for (n = 0; n < 256; n++) {
110  c = (z_crc_t)n;
111  for (k = 0; k < 8; k++)
112  c = c & 1 ? poly ^ (c >> 1) : c >> 1;
113  crc_table[0][n] = c;
114  }
115 
116 #ifdef BYFOUR
117  /* generate crc for each value followed by one, two, and three zeros,
118  and then the byte reversal of those as well as the first table */
119  for (n = 0; n < 256; n++) {
120  c = crc_table[0][n];
121  crc_table[4][n] = ZSWAP32(c);
122  for (k = 1; k < 4; k++) {
123  c = crc_table[0][c & 0xff] ^ (c >> 8);
124  crc_table[k][n] = c;
125  crc_table[k + 4][n] = ZSWAP32(c);
126  }
127  }
128 #endif /* BYFOUR */
129 
130  crc_table_empty = 0;
131  }
132  else { /* not first */
133  /* wait for the other guy to finish (not efficient, but rare) */
134  while (crc_table_empty)
135  ;
136  }
137 
138 #ifdef MAKECRCH
139  /* write out CRC tables to crc32.h */
140  {
141  FILE *out;
142 
143  out = fopen("crc32.h", "w");
144  if (out == NULL) return;
145  fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
146  fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
147  fprintf(out, "local const z_crc_t FAR ");
148  fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
149  write_table(out, crc_table[0]);
150 # ifdef BYFOUR
151  fprintf(out, "#ifdef BYFOUR\n");
152  for (k = 1; k < 8; k++) {
153  fprintf(out, " },\n {\n");
154  write_table(out, crc_table[k]);
155  }
156  fprintf(out, "#endif\n");
157 # endif /* BYFOUR */
158  fprintf(out, " }\n};\n");
159  fclose(out);
160  }
161 #endif /* MAKECRCH */
162 }
163 
164 #ifdef MAKECRCH
165 local void write_table(out, table)
166  FILE *out;
167  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  */
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_z(crc, buf, len)
203  unsigned long crc;
204  const unsigned char FAR *buf;
205  z_size_t len;
206 {
207  if (buf == Z_NULL) return 0UL;
208 
209 #ifdef DYNAMIC_CRC_TABLE
210  if (crc_table_empty)
211  make_crc_table();
212 #endif /* DYNAMIC_CRC_TABLE */
213 
214 #ifdef BYFOUR
215  if (sizeof(void *) == sizeof(ptrdiff_t)) {
216  z_crc_t endian;
217 
218  endian = 1;
219  if (*((unsigned char *)(&endian)))
220  return crc32_little(crc, buf, len);
221  else
222  return crc32_big(crc, buf, len);
223  }
224 #endif /* BYFOUR */
225  crc = crc ^ 0xffffffffUL;
226  while (len >= 8) {
227  DO8;
228  len -= 8;
229  }
230  if (len) do {
231  DO1;
232  } while (--len);
233  return crc ^ 0xffffffffUL;
234 }
235 
236 /* ========================================================================= */
237 unsigned long ZEXPORT crc32(crc, buf, len)
238  unsigned long crc;
239  const unsigned char FAR *buf;
240  uInt len;
241 {
242  return crc32_z(crc, buf, len);
243 }
244 
245 #ifdef BYFOUR
246 
247 /*
248  This BYFOUR code accesses the passed unsigned char * buffer with a 32-bit
249  integer pointer type. This violates the strict aliasing rule, where a
250  compiler can assume, for optimization purposes, that two pointers to
251  fundamentally different types won't ever point to the same memory. This can
252  manifest as a problem only if one of the pointers is written to. This code
253  only reads from those pointers. So long as this code remains isolated in
254  this compilation unit, there won't be a problem. For this reason, this code
255  should not be copied and pasted into a compilation unit in which other code
256  writes to the buffer that is passed to these routines.
257  */
258 
259 /* ========================================================================= */
260 #define DOLIT4 c ^= *buf4++; \
261  c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
262  crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
263 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
264 
265 /* ========================================================================= */
266 local unsigned long crc32_little(crc, buf, len)
267  unsigned long crc;
268  const unsigned char FAR *buf;
269  z_size_t len;
270 {
271  register z_crc_t c;
272  register const z_crc_t FAR *buf4;
273 
274  c = (z_crc_t)crc;
275  c = ~c;
276  while (len && ((ptrdiff_t)buf & 3)) {
277  c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
278  len--;
279  }
280 
281  buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
282  while (len >= 32) {
283  DOLIT32;
284  len -= 32;
285  }
286  while (len >= 4) {
287  DOLIT4;
288  len -= 4;
289  }
290  buf = (const unsigned char FAR *)buf4;
291 
292  if (len) do {
293  c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
294  } while (--len);
295  c = ~c;
296  return (unsigned long)c;
297 }
298 
299 /* ========================================================================= */
300 #define DOBIG4 c ^= *buf4++; \
301  c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
302  crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
303 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
304 
305 /* ========================================================================= */
306 local unsigned long crc32_big(crc, buf, len)
307  unsigned long crc;
308  const unsigned char FAR *buf;
309  z_size_t len;
310 {
311  register z_crc_t c;
312  register const z_crc_t FAR *buf4;
313 
314  c = ZSWAP32((z_crc_t)crc);
315  c = ~c;
316  while (len && ((ptrdiff_t)buf & 3)) {
317  c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
318  len--;
319  }
320 
321  buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
322  while (len >= 32) {
323  DOBIG32;
324  len -= 32;
325  }
326  while (len >= 4) {
327  DOBIG4;
328  len -= 4;
329  }
330  buf = (const unsigned char FAR *)buf4;
331 
332  if (len) do {
333  c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
334  } while (--len);
335  c = ~c;
336  return (unsigned long)(ZSWAP32(c));
337 }
338 
339 #endif /* BYFOUR */
340 
341 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
342 
343 /* ========================================================================= */
344 local unsigned long gf2_matrix_times(mat, vec)
345  unsigned long *mat;
346  unsigned long vec;
347 {
348  unsigned long sum;
349 
350  sum = 0;
351  while (vec) {
352  if (vec & 1)
353  sum ^= *mat;
354  vec >>= 1;
355  mat++;
356  }
357  return sum;
358 }
359 
360 /* ========================================================================= */
362  unsigned long *square;
363  unsigned long *mat;
364 {
365  int n;
366 
367  for (n = 0; n < GF2_DIM; n++)
368  square[n] = gf2_matrix_times(mat, mat[n]);
369 }
370 
371 /* ========================================================================= */
372 local uLong crc32_combine_(crc1, crc2, len2)
373  uLong crc1;
374  uLong crc2;
375  z_off64_t len2;
376 {
377  int n;
378  unsigned long row;
379  unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
380  unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
381 
382  /* degenerate case (also disallow negative lengths) */
383  if (len2 <= 0)
384  return crc1;
385 
386  /* put operator for one zero bit in odd */
387  odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
388  row = 1;
389  for (n = 1; n < GF2_DIM; n++) {
390  odd[n] = row;
391  row <<= 1;
392  }
393 
394  /* put operator for two zero bits in even */
396 
397  /* put operator for four zero bits in odd */
399 
400  /* apply len2 zeros to crc1 (first square will put the operator for one
401  zero byte, eight zero bits, in even) */
402  do {
403  /* apply zeros operator for this bit of len2 */
405  if (len2 & 1)
406  crc1 = gf2_matrix_times(even, crc1);
407  len2 >>= 1;
408 
409  /* if no more bits set, then done */
410  if (len2 == 0)
411  break;
412 
413  /* another iteration of the loop with odd and even swapped */
415  if (len2 & 1)
416  crc1 = gf2_matrix_times(odd, crc1);
417  len2 >>= 1;
418 
419  /* if no more bits set, then done */
420  } while (len2 != 0);
421 
422  /* return combined crc */
423  crc1 ^= crc2;
424  return crc1;
425 }
426 
427 /* ========================================================================= */
428 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
429  uLong crc1;
430  uLong crc2;
431  z_off_t len2;
432 {
433  return crc32_combine_(crc1, crc2, len2);
434 }
435 
436 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
437  uLong crc1;
438  uLong crc2;
439  z_off64_t len2;
440 {
441  return crc32_combine_(crc1, crc2, len2);
442 }
unsigned long z_size_t
Definition: zconf.h:250
unsigned long z_crc_t
Definition: zconf.h:431
uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.c:372
unsigned long ZEXPORT crc32_z(unsigned long crc, const unsigned char FAR *buf, z_size_t len)
Definition: crc32.c:202
uLong ZEXPORT crc32_combine64(uLong crc1, uLong crc2, z_off64_t len2)
Definition: crc32.c:436
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unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, uInt len)
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