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annotate libs/zlib/crc32.c @ 2:334d17aed7de

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author John Tsiombikas <nuclear@member.fsf.org>
date Sun, 02 Feb 2014 18:36:38 +0200
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nuclear@0 1 /* crc32.c -- compute the CRC-32 of a data stream
nuclear@0 2 * Copyright (C) 1995-2005 Mark Adler
nuclear@0 3 * For conditions of distribution and use, see copyright notice in zlib.h
nuclear@0 4 *
nuclear@0 5 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
nuclear@0 6 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
nuclear@0 7 * tables for updating the shift register in one step with three exclusive-ors
nuclear@0 8 * instead of four steps with four exclusive-ors. This results in about a
nuclear@0 9 * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
nuclear@0 10 */
nuclear@0 11
nuclear@0 12 /* @(#) $Id$ */
nuclear@0 13
nuclear@0 14 /*
nuclear@0 15 Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
nuclear@0 16 protection on the static variables used to control the first-use generation
nuclear@0 17 of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
nuclear@0 18 first call get_crc_table() to initialize the tables before allowing more than
nuclear@0 19 one thread to use crc32().
nuclear@0 20 */
nuclear@0 21
nuclear@0 22 #ifdef MAKECRCH
nuclear@0 23 # include <stdio.h>
nuclear@0 24 # ifndef DYNAMIC_CRC_TABLE
nuclear@0 25 # define DYNAMIC_CRC_TABLE
nuclear@0 26 # endif /* !DYNAMIC_CRC_TABLE */
nuclear@0 27 #endif /* MAKECRCH */
nuclear@0 28
nuclear@0 29 #include "zutil.h" /* for STDC and FAR definitions */
nuclear@0 30
nuclear@0 31 #define local static
nuclear@0 32
nuclear@0 33 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
nuclear@0 34 #ifndef NOBYFOUR
nuclear@0 35 # ifdef STDC /* need ANSI C limits.h to determine sizes */
nuclear@0 36 # include <limits.h>
nuclear@0 37 # define BYFOUR
nuclear@0 38 # if (UINT_MAX == 0xffffffffUL)
nuclear@0 39 typedef unsigned int u4;
nuclear@0 40 # else
nuclear@0 41 # if (ULONG_MAX == 0xffffffffUL)
nuclear@0 42 typedef unsigned long u4;
nuclear@0 43 # else
nuclear@0 44 # if (USHRT_MAX == 0xffffffffUL)
nuclear@0 45 typedef unsigned short u4;
nuclear@0 46 # else
nuclear@0 47 # undef BYFOUR /* can't find a four-byte integer type! */
nuclear@0 48 # endif
nuclear@0 49 # endif
nuclear@0 50 # endif
nuclear@0 51 # endif /* STDC */
nuclear@0 52 #endif /* !NOBYFOUR */
nuclear@0 53
nuclear@0 54 /* Definitions for doing the crc four data bytes at a time. */
nuclear@0 55 #ifdef BYFOUR
nuclear@0 56 # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
nuclear@0 57 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
nuclear@0 58 local unsigned long crc32_little OF((unsigned long,
nuclear@0 59 const unsigned char FAR *, unsigned));
nuclear@0 60 local unsigned long crc32_big OF((unsigned long,
nuclear@0 61 const unsigned char FAR *, unsigned));
nuclear@0 62 # define TBLS 8
nuclear@0 63 #else
nuclear@0 64 # define TBLS 1
nuclear@0 65 #endif /* BYFOUR */
nuclear@0 66
nuclear@0 67 /* Local functions for crc concatenation */
nuclear@0 68 local unsigned long gf2_matrix_times OF((unsigned long *mat,
nuclear@0 69 unsigned long vec));
nuclear@0 70 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
nuclear@0 71
nuclear@0 72 #ifdef DYNAMIC_CRC_TABLE
nuclear@0 73
nuclear@0 74 local volatile int crc_table_empty = 1;
nuclear@0 75 local unsigned long FAR crc_table[TBLS][256];
nuclear@0 76 local void make_crc_table OF((void));
nuclear@0 77 #ifdef MAKECRCH
nuclear@0 78 local void write_table OF((FILE *, const unsigned long FAR *));
nuclear@0 79 #endif /* MAKECRCH */
nuclear@0 80 /*
nuclear@0 81 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
nuclear@0 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.
nuclear@0 83
nuclear@0 84 Polynomials over GF(2) are represented in binary, one bit per coefficient,
nuclear@0 85 with the lowest powers in the most significant bit. Then adding polynomials
nuclear@0 86 is just exclusive-or, and multiplying a polynomial by x is a right shift by
nuclear@0 87 one. If we call the above polynomial p, and represent a byte as the
nuclear@0 88 polynomial q, also with the lowest power in the most significant bit (so the
nuclear@0 89 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
nuclear@0 90 where a mod b means the remainder after dividing a by b.
nuclear@0 91
nuclear@0 92 This calculation is done using the shift-register method of multiplying and
nuclear@0 93 taking the remainder. The register is initialized to zero, and for each
nuclear@0 94 incoming bit, x^32 is added mod p to the register if the bit is a one (where
nuclear@0 95 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
nuclear@0 96 x (which is shifting right by one and adding x^32 mod p if the bit shifted
nuclear@0 97 out is a one). We start with the highest power (least significant bit) of
nuclear@0 98 q and repeat for all eight bits of q.
nuclear@0 99
nuclear@0 100 The first table is simply the CRC of all possible eight bit values. This is
nuclear@0 101 all the information needed to generate CRCs on data a byte at a time for all
nuclear@0 102 combinations of CRC register values and incoming bytes. The remaining tables
nuclear@0 103 allow for word-at-a-time CRC calculation for both big-endian and little-
nuclear@0 104 endian machines, where a word is four bytes.
nuclear@0 105 */
nuclear@0 106 local void make_crc_table()
nuclear@0 107 {
nuclear@0 108 unsigned long c;
nuclear@0 109 int n, k;
nuclear@0 110 unsigned long poly; /* polynomial exclusive-or pattern */
nuclear@0 111 /* terms of polynomial defining this crc (except x^32): */
nuclear@0 112 static volatile int first = 1; /* flag to limit concurrent making */
nuclear@0 113 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
nuclear@0 114
nuclear@0 115 /* See if another task is already doing this (not thread-safe, but better
nuclear@0 116 than nothing -- significantly reduces duration of vulnerability in
nuclear@0 117 case the advice about DYNAMIC_CRC_TABLE is ignored) */
nuclear@0 118 if (first) {
nuclear@0 119 first = 0;
nuclear@0 120
nuclear@0 121 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
nuclear@0 122 poly = 0UL;
nuclear@0 123 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
nuclear@0 124 poly |= 1UL << (31 - p[n]);
nuclear@0 125
nuclear@0 126 /* generate a crc for every 8-bit value */
nuclear@0 127 for (n = 0; n < 256; n++) {
nuclear@0 128 c = (unsigned long)n;
nuclear@0 129 for (k = 0; k < 8; k++)
nuclear@0 130 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
nuclear@0 131 crc_table[0][n] = c;
nuclear@0 132 }
nuclear@0 133
nuclear@0 134 #ifdef BYFOUR
nuclear@0 135 /* generate crc for each value followed by one, two, and three zeros,
nuclear@0 136 and then the byte reversal of those as well as the first table */
nuclear@0 137 for (n = 0; n < 256; n++) {
nuclear@0 138 c = crc_table[0][n];
nuclear@0 139 crc_table[4][n] = REV(c);
nuclear@0 140 for (k = 1; k < 4; k++) {
nuclear@0 141 c = crc_table[0][c & 0xff] ^ (c >> 8);
nuclear@0 142 crc_table[k][n] = c;
nuclear@0 143 crc_table[k + 4][n] = REV(c);
nuclear@0 144 }
nuclear@0 145 }
nuclear@0 146 #endif /* BYFOUR */
nuclear@0 147
nuclear@0 148 crc_table_empty = 0;
nuclear@0 149 }
nuclear@0 150 else { /* not first */
nuclear@0 151 /* wait for the other guy to finish (not efficient, but rare) */
nuclear@0 152 while (crc_table_empty)
nuclear@0 153 ;
nuclear@0 154 }
nuclear@0 155
nuclear@0 156 #ifdef MAKECRCH
nuclear@0 157 /* write out CRC tables to crc32.h */
nuclear@0 158 {
nuclear@0 159 FILE *out;
nuclear@0 160
nuclear@0 161 out = fopen("crc32.h", "w");
nuclear@0 162 if (out == NULL) return;
nuclear@0 163 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
nuclear@0 164 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
nuclear@0 165 fprintf(out, "local const unsigned long FAR ");
nuclear@0 166 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
nuclear@0 167 write_table(out, crc_table[0]);
nuclear@0 168 # ifdef BYFOUR
nuclear@0 169 fprintf(out, "#ifdef BYFOUR\n");
nuclear@0 170 for (k = 1; k < 8; k++) {
nuclear@0 171 fprintf(out, " },\n {\n");
nuclear@0 172 write_table(out, crc_table[k]);
nuclear@0 173 }
nuclear@0 174 fprintf(out, "#endif\n");
nuclear@0 175 # endif /* BYFOUR */
nuclear@0 176 fprintf(out, " }\n};\n");
nuclear@0 177 fclose(out);
nuclear@0 178 }
nuclear@0 179 #endif /* MAKECRCH */
nuclear@0 180 }
nuclear@0 181
nuclear@0 182 #ifdef MAKECRCH
nuclear@0 183 local void write_table(out, table)
nuclear@0 184 FILE *out;
nuclear@0 185 const unsigned long FAR *table;
nuclear@0 186 {
nuclear@0 187 int n;
nuclear@0 188
nuclear@0 189 for (n = 0; n < 256; n++)
nuclear@0 190 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
nuclear@0 191 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
nuclear@0 192 }
nuclear@0 193 #endif /* MAKECRCH */
nuclear@0 194
nuclear@0 195 #else /* !DYNAMIC_CRC_TABLE */
nuclear@0 196 /* ========================================================================
nuclear@0 197 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
nuclear@0 198 */
nuclear@0 199 #include "crc32.h"
nuclear@0 200 #endif /* DYNAMIC_CRC_TABLE */
nuclear@0 201
nuclear@0 202 /* =========================================================================
nuclear@0 203 * This function can be used by asm versions of crc32()
nuclear@0 204 */
nuclear@0 205 const unsigned long FAR * ZEXPORT get_crc_table()
nuclear@0 206 {
nuclear@0 207 #ifdef DYNAMIC_CRC_TABLE
nuclear@0 208 if (crc_table_empty)
nuclear@0 209 make_crc_table();
nuclear@0 210 #endif /* DYNAMIC_CRC_TABLE */
nuclear@0 211 return (const unsigned long FAR *)crc_table;
nuclear@0 212 }
nuclear@0 213
nuclear@0 214 /* ========================================================================= */
nuclear@0 215 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
nuclear@0 216 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
nuclear@0 217
nuclear@0 218 /* ========================================================================= */
nuclear@0 219 unsigned long ZEXPORT crc32(crc, buf, len)
nuclear@0 220 unsigned long crc;
nuclear@0 221 const unsigned char FAR *buf;
nuclear@0 222 unsigned len;
nuclear@0 223 {
nuclear@0 224 if (buf == Z_NULL) return 0UL;
nuclear@0 225
nuclear@0 226 #ifdef DYNAMIC_CRC_TABLE
nuclear@0 227 if (crc_table_empty)
nuclear@0 228 make_crc_table();
nuclear@0 229 #endif /* DYNAMIC_CRC_TABLE */
nuclear@0 230
nuclear@0 231 #ifdef BYFOUR
nuclear@0 232 if (sizeof(void *) == sizeof(ptrdiff_t)) {
nuclear@0 233 u4 endian;
nuclear@0 234
nuclear@0 235 endian = 1;
nuclear@0 236 if (*((unsigned char *)(&endian)))
nuclear@0 237 return crc32_little(crc, buf, len);
nuclear@0 238 else
nuclear@0 239 return crc32_big(crc, buf, len);
nuclear@0 240 }
nuclear@0 241 #endif /* BYFOUR */
nuclear@0 242 crc = crc ^ 0xffffffffUL;
nuclear@0 243 while (len >= 8) {
nuclear@0 244 DO8;
nuclear@0 245 len -= 8;
nuclear@0 246 }
nuclear@0 247 if (len) do {
nuclear@0 248 DO1;
nuclear@0 249 } while (--len);
nuclear@0 250 return crc ^ 0xffffffffUL;
nuclear@0 251 }
nuclear@0 252
nuclear@0 253 #ifdef BYFOUR
nuclear@0 254
nuclear@0 255 /* ========================================================================= */
nuclear@0 256 #define DOLIT4 c ^= *buf4++; \
nuclear@0 257 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
nuclear@0 258 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
nuclear@0 259 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
nuclear@0 260
nuclear@0 261 /* ========================================================================= */
nuclear@0 262 local unsigned long crc32_little(crc, buf, len)
nuclear@0 263 unsigned long crc;
nuclear@0 264 const unsigned char FAR *buf;
nuclear@0 265 unsigned len;
nuclear@0 266 {
nuclear@0 267 register u4 c;
nuclear@0 268 register const u4 FAR *buf4;
nuclear@0 269
nuclear@0 270 c = (u4)crc;
nuclear@0 271 c = ~c;
nuclear@0 272 while (len && ((ptrdiff_t)buf & 3)) {
nuclear@0 273 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
nuclear@0 274 len--;
nuclear@0 275 }
nuclear@0 276
nuclear@0 277 buf4 = (const u4 FAR *)(const void FAR *)buf;
nuclear@0 278 while (len >= 32) {
nuclear@0 279 DOLIT32;
nuclear@0 280 len -= 32;
nuclear@0 281 }
nuclear@0 282 while (len >= 4) {
nuclear@0 283 DOLIT4;
nuclear@0 284 len -= 4;
nuclear@0 285 }
nuclear@0 286 buf = (const unsigned char FAR *)buf4;
nuclear@0 287
nuclear@0 288 if (len) do {
nuclear@0 289 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
nuclear@0 290 } while (--len);
nuclear@0 291 c = ~c;
nuclear@0 292 return (unsigned long)c;
nuclear@0 293 }
nuclear@0 294
nuclear@0 295 /* ========================================================================= */
nuclear@0 296 #define DOBIG4 c ^= *++buf4; \
nuclear@0 297 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
nuclear@0 298 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
nuclear@0 299 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
nuclear@0 300
nuclear@0 301 /* ========================================================================= */
nuclear@0 302 local unsigned long crc32_big(crc, buf, len)
nuclear@0 303 unsigned long crc;
nuclear@0 304 const unsigned char FAR *buf;
nuclear@0 305 unsigned len;
nuclear@0 306 {
nuclear@0 307 register u4 c;
nuclear@0 308 register const u4 FAR *buf4;
nuclear@0 309
nuclear@0 310 c = REV((u4)crc);
nuclear@0 311 c = ~c;
nuclear@0 312 while (len && ((ptrdiff_t)buf & 3)) {
nuclear@0 313 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
nuclear@0 314 len--;
nuclear@0 315 }
nuclear@0 316
nuclear@0 317 buf4 = (const u4 FAR *)(const void FAR *)buf;
nuclear@0 318 buf4--;
nuclear@0 319 while (len >= 32) {
nuclear@0 320 DOBIG32;
nuclear@0 321 len -= 32;
nuclear@0 322 }
nuclear@0 323 while (len >= 4) {
nuclear@0 324 DOBIG4;
nuclear@0 325 len -= 4;
nuclear@0 326 }
nuclear@0 327 buf4++;
nuclear@0 328 buf = (const unsigned char FAR *)buf4;
nuclear@0 329
nuclear@0 330 if (len) do {
nuclear@0 331 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
nuclear@0 332 } while (--len);
nuclear@0 333 c = ~c;
nuclear@0 334 return (unsigned long)(REV(c));
nuclear@0 335 }
nuclear@0 336
nuclear@0 337 #endif /* BYFOUR */
nuclear@0 338
nuclear@0 339 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
nuclear@0 340
nuclear@0 341 /* ========================================================================= */
nuclear@0 342 local unsigned long gf2_matrix_times(mat, vec)
nuclear@0 343 unsigned long *mat;
nuclear@0 344 unsigned long vec;
nuclear@0 345 {
nuclear@0 346 unsigned long sum;
nuclear@0 347
nuclear@0 348 sum = 0;
nuclear@0 349 while (vec) {
nuclear@0 350 if (vec & 1)
nuclear@0 351 sum ^= *mat;
nuclear@0 352 vec >>= 1;
nuclear@0 353 mat++;
nuclear@0 354 }
nuclear@0 355 return sum;
nuclear@0 356 }
nuclear@0 357
nuclear@0 358 /* ========================================================================= */
nuclear@0 359 local void gf2_matrix_square(square, mat)
nuclear@0 360 unsigned long *square;
nuclear@0 361 unsigned long *mat;
nuclear@0 362 {
nuclear@0 363 int n;
nuclear@0 364
nuclear@0 365 for (n = 0; n < GF2_DIM; n++)
nuclear@0 366 square[n] = gf2_matrix_times(mat, mat[n]);
nuclear@0 367 }
nuclear@0 368
nuclear@0 369 /* ========================================================================= */
nuclear@0 370 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
nuclear@0 371 uLong crc1;
nuclear@0 372 uLong crc2;
nuclear@0 373 z_off_t len2;
nuclear@0 374 {
nuclear@0 375 int n;
nuclear@0 376 unsigned long row;
nuclear@0 377 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
nuclear@0 378 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
nuclear@0 379
nuclear@0 380 /* degenerate case */
nuclear@0 381 if (len2 == 0)
nuclear@0 382 return crc1;
nuclear@0 383
nuclear@0 384 /* put operator for one zero bit in odd */
nuclear@0 385 odd[0] = 0xedb88320L; /* CRC-32 polynomial */
nuclear@0 386 row = 1;
nuclear@0 387 for (n = 1; n < GF2_DIM; n++) {
nuclear@0 388 odd[n] = row;
nuclear@0 389 row <<= 1;
nuclear@0 390 }
nuclear@0 391
nuclear@0 392 /* put operator for two zero bits in even */
nuclear@0 393 gf2_matrix_square(even, odd);
nuclear@0 394
nuclear@0 395 /* put operator for four zero bits in odd */
nuclear@0 396 gf2_matrix_square(odd, even);
nuclear@0 397
nuclear@0 398 /* apply len2 zeros to crc1 (first square will put the operator for one
nuclear@0 399 zero byte, eight zero bits, in even) */
nuclear@0 400 do {
nuclear@0 401 /* apply zeros operator for this bit of len2 */
nuclear@0 402 gf2_matrix_square(even, odd);
nuclear@0 403 if (len2 & 1)
nuclear@0 404 crc1 = gf2_matrix_times(even, crc1);
nuclear@0 405 len2 >>= 1;
nuclear@0 406
nuclear@0 407 /* if no more bits set, then done */
nuclear@0 408 if (len2 == 0)
nuclear@0 409 break;
nuclear@0 410
nuclear@0 411 /* another iteration of the loop with odd and even swapped */
nuclear@0 412 gf2_matrix_square(odd, even);
nuclear@0 413 if (len2 & 1)
nuclear@0 414 crc1 = gf2_matrix_times(odd, crc1);
nuclear@0 415 len2 >>= 1;
nuclear@0 416
nuclear@0 417 /* if no more bits set, then done */
nuclear@0 418 } while (len2 != 0);
nuclear@0 419
nuclear@0 420 /* return combined crc */
nuclear@0 421 crc1 ^= crc2;
nuclear@0 422 return crc1;
nuclear@0 423 }