1 /* crc32.c -- compute the CRC-32 of a data stream 2 * Copyright (C) 1995-2006, 2010, 2011 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 * 5 * Thanks to Rodney Brown <rbrown64 (at) 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 #define local static 34 35 /* Find a four-byte integer type for crc32_little() and crc32_big(). */ 36 #ifndef NOBYFOUR 37 # ifdef STDC /* need ANSI C limits.h to determine sizes */ 38 # include <limits.h> 39 # define BYFOUR 40 # if (UINT_MAX == 0xffffffffUL) 41 typedef unsigned int u4; 42 # else 43 # if (ULONG_MAX == 0xffffffffUL) 44 typedef unsigned long u4; 45 # else 46 # if (USHRT_MAX == 0xffffffffUL) 47 typedef unsigned short u4; 48 # else 49 # undef BYFOUR /* can't find a four-byte integer type! */ 50 # endif 51 # endif 52 # endif 53 # endif /* STDC */ 54 #endif /* !NOBYFOUR */ 55 56 /* Definitions for doing the crc four data bytes at a time. */ 57 #ifdef BYFOUR 58 typedef u4 crc_table_t; 59 # define REV(w) ((((w)>>24)&0xff)+(((w)>>8)&0xff00)+ \ 60 (((w)&0xff00)<<8)+(((w)&0xff)<<24)) 61 local unsigned long crc32_little OF((unsigned long, 62 const unsigned char FAR *, unsigned)); 63 local unsigned long crc32_big OF((unsigned long, 64 const unsigned char FAR *, unsigned)); 65 # define TBLS 8 66 #else 67 typedef unsigned long crc_table_t; 68 # define TBLS 1 69 #endif /* BYFOUR */ 70 71 /* Local functions for crc concatenation */ 72 local unsigned long gf2_matrix_times OF((unsigned long *mat, 73 unsigned long vec)); 74 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); 75 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2)); 76 77 78 #ifdef DYNAMIC_CRC_TABLE 79 80 local volatile int crc_table_empty = 1; 81 local crc_table_t FAR crc_table[TBLS][256]; 82 local void make_crc_table OF((void)); 83 #ifdef MAKECRCH 84 local void write_table OF((FILE *, const crc_table_t FAR *)); 85 #endif /* MAKECRCH */ 86 /* 87 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: 88 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. 89 90 Polynomials over GF(2) are represented in binary, one bit per coefficient, 91 with the lowest powers in the most significant bit. Then adding polynomials 92 is just exclusive-or, and multiplying a polynomial by x is a right shift by 93 one. If we call the above polynomial p, and represent a byte as the 94 polynomial q, also with the lowest power in the most significant bit (so the 95 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, 96 where a mod b means the remainder after dividing a by b. 97 98 This calculation is done using the shift-register method of multiplying and 99 taking the remainder. The register is initialized to zero, and for each 100 incoming bit, x^32 is added mod p to the register if the bit is a one (where 101 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by 102 x (which is shifting right by one and adding x^32 mod p if the bit shifted 103 out is a one). We start with the highest power (least significant bit) of 104 q and repeat for all eight bits of q. 105 106 The first table is simply the CRC of all possible eight bit values. This is 107 all the information needed to generate CRCs on data a byte at a time for all 108 combinations of CRC register values and incoming bytes. The remaining tables 109 allow for word-at-a-time CRC calculation for both big-endian and little- 110 endian machines, where a word is four bytes. 111 */ 112 local void make_crc_table() 113 { 114 crc_table_t c; 115 int n, k; 116 crc_table_t poly; /* polynomial exclusive-or pattern */ 117 /* terms of polynomial defining this crc (except x^32): */ 118 static volatile int first = 1; /* flag to limit concurrent making */ 119 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; 120 121 /* See if another task is already doing this (not thread-safe, but better 122 than nothing -- significantly reduces duration of vulnerability in 123 case the advice about DYNAMIC_CRC_TABLE is ignored) */ 124 if (first) { 125 first = 0; 126 127 /* make exclusive-or pattern from polynomial (0xedb88320UL) */ 128 poly = 0; 129 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++) 130 poly |= (crc_table_t)1 << (31 - p[n]); 131 132 /* generate a crc for every 8-bit value */ 133 for (n = 0; n < 256; n++) { 134 c = (crc_table_t)n; 135 for (k = 0; k < 8; k++) 136 c = c & 1 ? poly ^ (c >> 1) : c >> 1; 137 crc_table[0][n] = c; 138 } 139 140 #ifdef BYFOUR 141 /* generate crc for each value followed by one, two, and three zeros, 142 and then the byte reversal of those as well as the first table */ 143 for (n = 0; n < 256; n++) { 144 c = crc_table[0][n]; 145 crc_table[4][n] = REV(c); 146 for (k = 1; k < 4; k++) { 147 c = crc_table[0][c & 0xff] ^ (c >> 8); 148 crc_table[k][n] = c; 149 crc_table[k + 4][n] = REV(c); 150 } 151 } 152 #endif /* BYFOUR */ 153 154 crc_table_empty = 0; 155 } 156 else { /* not first */ 157 /* wait for the other guy to finish (not efficient, but rare) */ 158 while (crc_table_empty) 159 ; 160 } 161 162 #ifdef MAKECRCH 163 /* write out CRC tables to crc32.h */ 164 { 165 FILE *out; 166 167 out = fopen("crc32.h", "w"); 168 if (out == NULL) return; 169 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); 170 fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); 171 fprintf(out, "local const crc_table_t FAR "); 172 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); 173 write_table(out, crc_table[0]); 174 # ifdef BYFOUR 175 fprintf(out, "#ifdef BYFOUR\n"); 176 for (k = 1; k < 8; k++) { 177 fprintf(out, " },\n {\n"); 178 write_table(out, crc_table[k]); 179 } 180 fprintf(out, "#endif\n"); 181 # endif /* BYFOUR */ 182 fprintf(out, " }\n};\n"); 183 fclose(out); 184 } 185 #endif /* MAKECRCH */ 186 } 187 188 #ifdef MAKECRCH 189 local void write_table(out, table) 190 FILE *out; 191 const crc_table_t FAR *table; 192 { 193 int n; 194 195 for (n = 0; n < 256; n++) 196 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", 197 (unsigned long)(table[n]), 198 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); 199 } 200 #endif /* MAKECRCH */ 201 202 #else /* !DYNAMIC_CRC_TABLE */ 203 /* ======================================================================== 204 * Tables of CRC-32s of all single-byte values, made by make_crc_table(). 205 */ 206 #include "crc32.h" 207 #endif /* DYNAMIC_CRC_TABLE */ 208 209 /* ========================================================================= 210 * This function can be used by asm versions of crc32() 211 */ 212 const unsigned long FAR * ZEXPORT get_crc_table() 213 { 214 #ifdef DYNAMIC_CRC_TABLE 215 if (crc_table_empty) 216 make_crc_table(); 217 #endif /* DYNAMIC_CRC_TABLE */ 218 return (const unsigned long FAR *)crc_table; 219 } 220 221 /* ========================================================================= */ 222 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) 223 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 224 225 /* ========================================================================= */ 226 unsigned long ZEXPORT crc32(crc, buf, len) 227 unsigned long crc; 228 const unsigned char FAR *buf; 229 uInt len; 230 { 231 if (buf == Z_NULL) return 0UL; 232 233 #ifdef DYNAMIC_CRC_TABLE 234 if (crc_table_empty) 235 make_crc_table(); 236 #endif /* DYNAMIC_CRC_TABLE */ 237 238 #ifdef BYFOUR 239 if (sizeof(void *) == sizeof(ptrdiff_t)) { 240 u4 endian; 241 242 endian = 1; 243 if (*((unsigned char *)(&endian))) 244 return crc32_little(crc, buf, len); 245 else 246 return crc32_big(crc, buf, len); 247 } 248 #endif /* BYFOUR */ 249 crc = crc ^ 0xffffffffUL; 250 while (len >= 8) { 251 DO8; 252 len -= 8; 253 } 254 if (len) do { 255 DO1; 256 } while (--len); 257 return crc ^ 0xffffffffUL; 258 } 259 260 #ifdef BYFOUR 261 262 /* ========================================================================= */ 263 #define DOLIT4 c ^= *buf4++; \ 264 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ 265 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] 266 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 267 268 /* ========================================================================= */ 269 local unsigned long crc32_little(crc, buf, len) 270 unsigned long crc; 271 const unsigned char FAR *buf; 272 unsigned len; 273 { 274 register u4 c; 275 register const u4 FAR *buf4; 276 277 c = (u4)crc; 278 c = ~c; 279 while (len && ((ptrdiff_t)buf & 3)) { 280 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 281 len--; 282 } 283 284 buf4 = (const u4 FAR *)(const void FAR *)buf; 285 while (len >= 32) { 286 DOLIT32; 287 len -= 32; 288 } 289 while (len >= 4) { 290 DOLIT4; 291 len -= 4; 292 } 293 buf = (const unsigned char FAR *)buf4; 294 295 if (len) do { 296 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 297 } while (--len); 298 c = ~c; 299 return (unsigned long)c; 300 } 301 302 /* ========================================================================= */ 303 #define DOBIG4 c ^= *++buf4; \ 304 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ 305 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] 306 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 307 308 /* ========================================================================= */ 309 local unsigned long crc32_big(crc, buf, len) 310 unsigned long crc; 311 const unsigned char FAR *buf; 312 unsigned len; 313 { 314 register u4 c; 315 register const u4 FAR *buf4; 316 317 c = REV((u4)crc); 318 c = ~c; 319 while (len && ((ptrdiff_t)buf & 3)) { 320 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 321 len--; 322 } 323 324 buf4 = (const u4 FAR *)(const void FAR *)buf; 325 buf4--; 326 while (len >= 32) { 327 DOBIG32; 328 len -= 32; 329 } 330 while (len >= 4) { 331 DOBIG4; 332 len -= 4; 333 } 334 buf4++; 335 buf = (const unsigned char FAR *)buf4; 336 337 if (len) do { 338 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 339 } while (--len); 340 c = ~c; 341 return (unsigned long)(REV(c)); 342 } 343 344 #endif /* BYFOUR */ 345 346 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ 347 348 /* ========================================================================= */ 349 local unsigned long gf2_matrix_times(mat, vec) 350 unsigned long *mat; 351 unsigned long vec; 352 { 353 unsigned long sum; 354 355 sum = 0; 356 while (vec) { 357 if (vec & 1) 358 sum ^= *mat; 359 vec >>= 1; 360 mat++; 361 } 362 return sum; 363 } 364 365 /* ========================================================================= */ 366 local void gf2_matrix_square(square, mat) 367 unsigned long *square; 368 unsigned long *mat; 369 { 370 int n; 371 372 for (n = 0; n < GF2_DIM; n++) 373 square[n] = gf2_matrix_times(mat, mat[n]); 374 } 375 376 /* ========================================================================= */ 377 local uLong crc32_combine_(crc1, crc2, len2) 378 uLong crc1; 379 uLong crc2; 380 z_off64_t len2; 381 { 382 int n; 383 unsigned long row; 384 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ 385 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ 386 387 /* degenerate case (also disallow negative lengths) */ 388 if (len2 <= 0) 389 return crc1; 390 391 /* put operator for one zero bit in odd */ 392 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */ 393 row = 1; 394 for (n = 1; n < GF2_DIM; n++) { 395 odd[n] = row; 396 row <<= 1; 397 } 398 399 /* put operator for two zero bits in even */ 400 gf2_matrix_square(even, odd); 401 402 /* put operator for four zero bits in odd */ 403 gf2_matrix_square(odd, even); 404 405 /* apply len2 zeros to crc1 (first square will put the operator for one 406 zero byte, eight zero bits, in even) */ 407 do { 408 /* apply zeros operator for this bit of len2 */ 409 gf2_matrix_square(even, odd); 410 if (len2 & 1) 411 crc1 = gf2_matrix_times(even, crc1); 412 len2 >>= 1; 413 414 /* if no more bits set, then done */ 415 if (len2 == 0) 416 break; 417 418 /* another iteration of the loop with odd and even swapped */ 419 gf2_matrix_square(odd, even); 420 if (len2 & 1) 421 crc1 = gf2_matrix_times(odd, crc1); 422 len2 >>= 1; 423 424 /* if no more bits set, then done */ 425 } while (len2 != 0); 426 427 /* return combined crc */ 428 crc1 ^= crc2; 429 return crc1; 430 } 431 432 /* ========================================================================= */ 433 uLong ZEXPORT crc32_combine(crc1, crc2, len2) 434 uLong crc1; 435 uLong crc2; 436 z_off_t len2; 437 { 438 return crc32_combine_(crc1, crc2, len2); 439 } 440 441 uLong ZEXPORT crc32_combine64(crc1, crc2, len2) 442 uLong crc1; 443 uLong crc2; 444 z_off64_t len2; 445 { 446 return crc32_combine_(crc1, crc2, len2); 447 } 448
