Martin v. Löwis | d372aa8 | 2006-01-03 06:44:59 +0000 | [diff] [blame^] | 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 | } |