crc32.c
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1 /* crc32.c -- compute the CRC-32 of a data stream
2  * Copyright (C) 1995-2005 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 
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)+(((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 
72 #ifdef DYNAMIC_CRC_TABLE
73 
74 local volatile int crc_table_empty = 1;
75 local unsigned long FAR crc_table[TBLS][256];
76 local void make_crc_table OF((void));
77 #ifdef MAKECRCH
78  local void write_table OF((FILE *, const unsigned long FAR *));
79 #endif /* MAKECRCH */
80 /*
81  Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
82  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.
83 
84  Polynomials over GF(2) are represented in binary, one bit per coefficient,
85  with the lowest powers in the most significant bit. Then adding polynomials
86  is just exclusive-or, and multiplying a polynomial by x is a right shift by
87  one. If we call the above polynomial p, and represent a byte as the
88  polynomial q, also with the lowest power in the most significant bit (so the
89  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
90  where a mod b means the remainder after dividing a by b.
91 
92  This calculation is done using the shift-register method of multiplying and
93  taking the remainder. The register is initialized to zero, and for each
94  incoming bit, x^32 is added mod p to the register if the bit is a one (where
95  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
96  x (which is shifting right by one and adding x^32 mod p if the bit shifted
97  out is a one). We start with the highest power (least significant bit) of
98  q and repeat for all eight bits of q.
99 
100  The first table is simply the CRC of all possible eight bit values. This is
101  all the information needed to generate CRCs on data a byte at a time for all
102  combinations of CRC register values and incoming bytes. The remaining tables
103  allow for word-at-a-time CRC calculation for both big-endian and little-
104  endian machines, where a word is four bytes.
105 */
106 local void make_crc_table()
107 {
108  unsigned long c;
109  int n, k;
110  unsigned long poly; /* polynomial exclusive-or pattern */
111  /* terms of polynomial defining this crc (except x^32): */
112  static volatile int first = 1; /* flag to limit concurrent making */
113  static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
114 
115  /* See if another task is already doing this (not thread-safe, but better
116  than nothing -- significantly reduces duration of vulnerability in
117  case the advice about DYNAMIC_CRC_TABLE is ignored) */
118  if (first) {
119  first = 0;
120 
121  /* make exclusive-or pattern from polynomial (0xedb88320UL) */
122  poly = 0UL;
123  for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
124  poly |= 1UL << (31 - p[n]);
125 
126  /* generate a crc for every 8-bit value */
127  for (n = 0; n < 256; n++) {
128  c = (unsigned long)n;
129  for (k = 0; k < 8; k++)
130  c = c & 1 ? poly ^ (c >> 1) : c >> 1;
131  crc_table[0][n] = c;
132  }
133 
134 #ifdef BYFOUR
135  /* generate crc for each value followed by one, two, and three zeros,
136  and then the byte reversal of those as well as the first table */
137  for (n = 0; n < 256; n++) {
138  c = crc_table[0][n];
139  crc_table[4][n] = REV(c);
140  for (k = 1; k < 4; k++) {
141  c = crc_table[0][c & 0xff] ^ (c >> 8);
142  crc_table[k][n] = c;
143  crc_table[k + 4][n] = REV(c);
144  }
145  }
146 #endif /* BYFOUR */
147 
148  crc_table_empty = 0;
149  }
150  else { /* not first */
151  /* wait for the other guy to finish (not efficient, but rare) */
152  while (crc_table_empty)
153  ;
154  }
155 
156 #ifdef MAKECRCH
157  /* write out CRC tables to crc32.h */
158  {
159  FILE *out;
160 
161  out = fopen("crc32.h", "w");
162  if (out == NULL) return;
163  fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
164  fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
165  fprintf(out, "local const unsigned long FAR ");
166  fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
167  write_table(out, crc_table[0]);
168 # ifdef BYFOUR
169  fprintf(out, "#ifdef BYFOUR\n");
170  for (k = 1; k < 8; k++) {
171  fprintf(out, " },\n {\n");
172  write_table(out, crc_table[k]);
173  }
174  fprintf(out, "#endif\n");
175 # endif /* BYFOUR */
176  fprintf(out, " }\n};\n");
177  fclose(out);
178  }
179 #endif /* MAKECRCH */
180 }
181 
182 #ifdef MAKECRCH
183 local void write_table(out, table)
184  FILE *out;
185  const unsigned long FAR *table;
186 {
187  int n;
188 
189  for (n = 0; n < 256; n++)
190  fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
191  n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
192 }
193 #endif /* MAKECRCH */
194 
195 #else /* !DYNAMIC_CRC_TABLE */
196 /* ========================================================================
197  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
198  */
199 #include "crc32.h"
200 #endif /* DYNAMIC_CRC_TABLE */
201 
202 /* =========================================================================
203  * This function can be used by asm versions of crc32()
204  */
205 const unsigned long FAR * ZEXPORT get_crc_table()
206 {
207 #ifdef DYNAMIC_CRC_TABLE
208  if (crc_table_empty)
209  make_crc_table();
210 #endif /* DYNAMIC_CRC_TABLE */
211  return (const unsigned long FAR *)crc_table;
212 }
213 
214 /* ========================================================================= */
215 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
216 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
217 
218 /* ========================================================================= */
219 unsigned long ZEXPORT crc32(crc, buf, len)
220  unsigned long crc;
221  const unsigned char FAR *buf;
222  unsigned len;
223 {
224  if (buf == Z_NULL) return 0UL;
225 
226 #ifdef DYNAMIC_CRC_TABLE
227  if (crc_table_empty)
228  make_crc_table();
229 #endif /* DYNAMIC_CRC_TABLE */
230 
231 #ifdef BYFOUR
232  if (sizeof(void *) == sizeof(ptrdiff_t)) {
233  u4 endian;
234 
235  endian = 1;
236  if (*((unsigned char *)(&endian)))
237  return crc32_little(crc, buf, len);
238  else
239  return crc32_big(crc, buf, len);
240  }
241 #endif /* BYFOUR */
242  crc = crc ^ 0xffffffffUL;
243  while (len >= 8) {
244  DO8;
245  len -= 8;
246  }
247  if (len) do {
248  DO1;
249  } while (--len);
250  return crc ^ 0xffffffffUL;
251 }
252 
253 #ifdef BYFOUR
254 
255 /* ========================================================================= */
256 #define DOLIT4 c ^= *buf4++; \
257  c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
258  crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
259 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
260 
261 /* ========================================================================= */
262 local unsigned long crc32_little(crc, buf, len)
263  unsigned long crc;
264  const unsigned char FAR *buf;
265  unsigned len;
266 {
267  register u4 c;
268  register const u4 FAR *buf4;
269 
270  c = (u4)crc;
271  c = ~c;
272  while (len && ((ptrdiff_t)buf & 3)) {
273  c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
274  len--;
275  }
276 
277  buf4 = (const u4 FAR *)(const void FAR *)buf;
278  while (len >= 32) {
279  DOLIT32;
280  len -= 32;
281  }
282  while (len >= 4) {
283  DOLIT4;
284  len -= 4;
285  }
286  buf = (const unsigned char FAR *)buf4;
287 
288  if (len) do {
289  c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
290  } while (--len);
291  c = ~c;
292  return (unsigned long)c;
293 }
294 
295 /* ========================================================================= */
296 #define DOBIG4 c ^= *++buf4; \
297  c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
298  crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
299 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
300 
301 /* ========================================================================= */
302 local unsigned long crc32_big(crc, buf, len)
303  unsigned long crc;
304  const unsigned char FAR *buf;
305  unsigned len;
306 {
307  register u4 c;
308  register const u4 FAR *buf4;
309 
310  c = REV((u4)crc);
311  c = ~c;
312  while (len && ((ptrdiff_t)buf & 3)) {
313  c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
314  len--;
315  }
316 
317  buf4 = (const u4 FAR *)(const void FAR *)buf;
318  buf4--;
319  while (len >= 32) {
320  DOBIG32;
321  len -= 32;
322  }
323  while (len >= 4) {
324  DOBIG4;
325  len -= 4;
326  }
327  buf4++;
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 /* ========================================================================= */
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 /* ========================================================================= */
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 /* ========================================================================= */
370 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
371  uLong crc1;
372  uLong crc2;
373  z_off_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 */
381  if (len2 == 0)
382  return crc1;
383 
384  /* put operator for one zero bit in odd */
385  odd[0] = 0xedb88320L; /* 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 }
get_crc_table
const unsigned long FAR *ZEXPORT get_crc_table()
Definition: crc32.c:205
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unsigned long gf2_matrix_times(unsigned long *mat, unsigned long vec)
Definition: crc32.c:342
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#define DO1
Definition: crc32.c:215
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uLong ZEXPORT crc32_combine(uLong crc1, uLong crc2, z_off_t len2)
Definition: crc32.c:370
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unsigned long uLong
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#define TBLS
Definition: crc32.c:64
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#define z_off_t
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#define GF2_DIM
Definition: crc32.c:339
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#define Z_NULL
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unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, unsigned len)
Definition: crc32.c:219
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Definition: crc32.c:216


openhrp3
Author(s): AIST, General Robotix Inc., Nakamura Lab of Dept. of Mechano Informatics at University of Tokyo
autogenerated on Wed Sep 7 2022 02:51:02