Masahiro Yamada | 221b163 | 2018-01-26 11:42:01 +0900 | [diff] [blame] | 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; |
| 57 | local z_crc_t FAR crc_table[TBLS][256]; |
| 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 | */ |
| 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_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 | /* ========================================================================= */ |
| 361 | local void gf2_matrix_square(square, mat) |
| 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 */ |
| 395 | gf2_matrix_square(even, odd); |
| 396 | |
| 397 | /* put operator for four zero bits in odd */ |
| 398 | gf2_matrix_square(odd, even); |
| 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 */ |
| 404 | gf2_matrix_square(even, odd); |
| 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 */ |
| 414 | gf2_matrix_square(odd, even); |
| 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 | } |