1 /* 2 * Copyright 2007 Sun Microsystems, Inc. All rights reserved. 3 * Use is subject to license terms. 4 */ 5 6 /* crc32.c -- compute the CRC-32 of a data stream 7 * Copyright (C) 1995-2005 Mark Adler 8 * For conditions of distribution and use, see copyright notice in zlib.h 9 * 10 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster 11 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing 12 * tables for updating the shift register in one step with three exclusive-ors 13 * instead of four steps with four exclusive-ors. This results in about a 14 * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. 15 */ 16 17 #pragma ident "%Z%%M% %I% %E% SMI" 18 19 /* 20 Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore 21 protection on the static variables used to control the first-use generation 22 of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should 23 first call get_crc_table() to initialize the tables before allowing more than 24 one thread to use crc32(). 25 */ 26 27 #ifdef MAKECRCH 28 # include <stdio.h> 29 # ifndef DYNAMIC_CRC_TABLE 30 # define DYNAMIC_CRC_TABLE 31 # endif /* !DYNAMIC_CRC_TABLE */ 32 #endif /* MAKECRCH */ 33 34 #include "zutil.h" /* for STDC and FAR definitions */ 35 36 #define local static 37 38 /* Find a four-byte integer type for crc32_little() and crc32_big(). */ 39 #ifndef NOBYFOUR 40 # ifdef STDC /* need ANSI C limits.h to determine sizes */ 41 # include <limits.h> 42 # define BYFOUR 43 # if (UINT_MAX == 0xffffffffUL) 44 typedef unsigned int u4; 45 # else 46 # if (ULONG_MAX == 0xffffffffUL) 47 typedef unsigned long u4; 48 # else 49 # if (USHRT_MAX == 0xffffffffUL) 50 typedef unsigned short u4; 51 # else 52 # undef BYFOUR /* can't find a four-byte integer type! */ 53 # endif 54 # endif 55 # endif 56 # endif /* STDC */ 57 #endif /* !NOBYFOUR */ 58 59 /* Definitions for doing the crc four data bytes at a time. */ 60 #ifdef BYFOUR 61 # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ 62 (((w)&0xff00)<<8)+(((w)&0xff)<<24)) 63 local unsigned long crc32_little OF((unsigned long, 64 const unsigned char FAR *, unsigned)); 65 local unsigned long crc32_big OF((unsigned long, 66 const unsigned char FAR *, unsigned)); 67 # define TBLS 8 68 #else 69 # define TBLS 1 70 #endif /* BYFOUR */ 71 72 /* Local functions for crc concatenation */ 73 local unsigned long gf2_matrix_times OF((unsigned long *mat, 74 unsigned long vec)); 75 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); 76 77 #ifdef DYNAMIC_CRC_TABLE 78 79 local volatile int crc_table_empty = 1; 80 local unsigned long FAR crc_table[TBLS][256]; 81 local void make_crc_table OF((void)); 82 #ifdef MAKECRCH 83 local void write_table OF((FILE *, const unsigned long FAR *)); 84 #endif /* MAKECRCH */ 85 /* 86 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: 87 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. 88 89 Polynomials over GF(2) are represented in binary, one bit per coefficient, 90 with the lowest powers in the most significant bit. Then adding polynomials 91 is just exclusive-or, and multiplying a polynomial by x is a right shift by 92 one. If we call the above polynomial p, and represent a byte as the 93 polynomial q, also with the lowest power in the most significant bit (so the 94 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, 95 where a mod b means the remainder after dividing a by b. 96 97 This calculation is done using the shift-register method of multiplying and 98 taking the remainder. The register is initialized to zero, and for each 99 incoming bit, x^32 is added mod p to the register if the bit is a one (where 100 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by 101 x (which is shifting right by one and adding x^32 mod p if the bit shifted 102 out is a one). We start with the highest power (least significant bit) of 103 q and repeat for all eight bits of q. 104 105 The first table is simply the CRC of all possible eight bit values. This is 106 all the information needed to generate CRCs on data a byte at a time for all 107 combinations of CRC register values and incoming bytes. The remaining tables 108 allow for word-at-a-time CRC calculation for both big-endian and little- 109 endian machines, where a word is four bytes. 110 */ 111 local void make_crc_table() 112 { 113 unsigned long c; 114 int n, k; 115 unsigned long poly; /* polynomial exclusive-or pattern */ 116 /* terms of polynomial defining this crc (except x^32): */ 117 static volatile int first = 1; /* flag to limit concurrent making */ 118 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; 119 120 /* See if another task is already doing this (not thread-safe, but better 121 than nothing -- significantly reduces duration of vulnerability in 122 case the advice about DYNAMIC_CRC_TABLE is ignored) */ 123 if (first) { 124 first = 0; 125 126 /* make exclusive-or pattern from polynomial (0xedb88320UL) */ 127 poly = 0UL; 128 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) 129 poly |= 1UL << (31 - p[n]); 130 131 /* generate a crc for every 8-bit value */ 132 for (n = 0; n < 256; n++) { 133 c = (unsigned long)n; 134 for (k = 0; k < 8; k++) 135 c = c & 1 ? poly ^ (c >> 1) : c >> 1; 136 crc_table[0][n] = c; 137 } 138 139 #ifdef BYFOUR 140 /* generate crc for each value followed by one, two, and three zeros, 141 and then the byte reversal of those as well as the first table */ 142 for (n = 0; n < 256; n++) { 143 c = crc_table[0][n]; 144 crc_table[4][n] = REV(c); 145 for (k = 1; k < 4; k++) { 146 c = crc_table[0][c & 0xff] ^ (c >> 8); 147 crc_table[k][n] = c; 148 crc_table[k + 4][n] = REV(c); 149 } 150 } 151 #endif /* BYFOUR */ 152 153 crc_table_empty = 0; 154 } 155 else { /* not first */ 156 /* wait for the other guy to finish (not efficient, but rare) */ 157 while (crc_table_empty) 158 ; 159 } 160 161 #ifdef MAKECRCH 162 /* write out CRC tables to crc32.h */ 163 { 164 FILE *out; 165 166 out = fopen("crc32.h", "w"); 167 if (out == NULL) return; 168 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); 169 fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); 170 fprintf(out, "local const unsigned long FAR "); 171 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); 172 write_table(out, crc_table[0]); 173 # ifdef BYFOUR 174 fprintf(out, "#ifdef BYFOUR\n"); 175 for (k = 1; k < 8; k++) { 176 fprintf(out, " },\n {\n"); 177 write_table(out, crc_table[k]); 178 } 179 fprintf(out, "#endif\n"); 180 # endif /* BYFOUR */ 181 fprintf(out, " }\n};\n"); 182 fclose(out); 183 } 184 #endif /* MAKECRCH */ 185 } 186 187 #ifdef MAKECRCH 188 local void write_table(out, table) 189 FILE *out; 190 const unsigned long FAR *table; 191 { 192 int n; 193 194 for (n = 0; n < 256; n++) 195 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n], 196 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); 197 } 198 #endif /* MAKECRCH */ 199 200 #else /* !DYNAMIC_CRC_TABLE */ 201 /* ======================================================================== 202 * Tables of CRC-32s of all single-byte values, made by make_crc_table(). 203 */ 204 #include "crc32.h" 205 #endif /* DYNAMIC_CRC_TABLE */ 206 207 /* ========================================================================= 208 * This function can be used by asm versions of crc32() 209 */ 210 const unsigned long FAR * ZEXPORT get_crc_table() 211 { 212 #ifdef DYNAMIC_CRC_TABLE 213 if (crc_table_empty) 214 make_crc_table(); 215 #endif /* DYNAMIC_CRC_TABLE */ 216 return (const unsigned long FAR *)crc_table; 217 } 218 219 /* ========================================================================= */ 220 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) 221 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 222 223 /* ========================================================================= */ 224 unsigned long ZEXPORT crc32(crc, buf, len) 225 unsigned long crc; 226 const unsigned char FAR *buf; 227 unsigned len; 228 { 229 if (buf == Z_NULL) return 0UL; 230 231 #ifdef DYNAMIC_CRC_TABLE 232 if (crc_table_empty) 233 make_crc_table(); 234 #endif /* DYNAMIC_CRC_TABLE */ 235 236 #ifdef BYFOUR 237 if (sizeof(void *) == sizeof(ptrdiff_t)) { 238 u4 endian; 239 240 endian = 1; 241 if (*((unsigned char *)(&endian))) 242 return crc32_little(crc, buf, len); 243 else 244 return crc32_big(crc, buf, len); 245 } 246 #endif /* BYFOUR */ 247 crc = crc ^ 0xffffffffUL; 248 while (len >= 8) { 249 DO8; 250 len -= 8; 251 } 252 if (len) do { 253 DO1; 254 } while (--len); 255 return crc ^ 0xffffffffUL; 256 } 257 258 #ifdef BYFOUR 259 260 /* ========================================================================= */ 261 #define DOLIT4 c ^= *buf4++; \ 262 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ 263 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] 264 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 265 266 /* ========================================================================= */ 267 local unsigned long crc32_little(crc, buf, len) 268 unsigned long crc; 269 const unsigned char FAR *buf; 270 unsigned len; 271 { 272 register u4 c; 273 register const u4 FAR *buf4; 274 275 c = (u4)crc; 276 c = ~c; 277 while (len && ((ptrdiff_t)buf & 3)) { 278 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 279 len--; 280 } 281 282 buf4 = (const u4 FAR *)(const void FAR *)buf; 283 while (len >= 32) { 284 DOLIT32; 285 len -= 32; 286 } 287 while (len >= 4) { 288 DOLIT4; 289 len -= 4; 290 } 291 buf = (const unsigned char FAR *)buf4; 292 293 if (len) do { 294 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 295 } while (--len); 296 c = ~c; 297 return (unsigned long)c; 298 } 299 300 /* ========================================================================= */ 301 #define DOBIG4 c ^= *++buf4; \ 302 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ 303 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] 304 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 305 306 /* ========================================================================= */ 307 local unsigned long crc32_big(crc, buf, len) 308 unsigned long crc; 309 const unsigned char FAR *buf; 310 unsigned len; 311 { 312 register u4 c; 313 register const u4 FAR *buf4; 314 315 c = REV((u4)crc); 316 c = ~c; 317 while (len && ((ptrdiff_t)buf & 3)) { 318 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 319 len--; 320 } 321 322 buf4 = (const u4 FAR *)(const void FAR *)buf; 323 buf4--; 324 while (len >= 32) { 325 DOBIG32; 326 len -= 32; 327 } 328 while (len >= 4) { 329 DOBIG4; 330 len -= 4; 331 } 332 buf4++; 333 buf = (const unsigned char FAR *)buf4; 334 335 if (len) do { 336 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 337 } while (--len); 338 c = ~c; 339 return (unsigned long)(REV(c)); 340 } 341 342 #endif /* BYFOUR */ 343 344 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ 345 346 /* ========================================================================= */ 347 local unsigned long gf2_matrix_times(mat, vec) 348 unsigned long *mat; 349 unsigned long vec; 350 { 351 unsigned long sum; 352 353 sum = 0; 354 while (vec) { 355 if (vec & 1) 356 sum ^= *mat; 357 vec >>= 1; 358 mat++; 359 } 360 return sum; 361 } 362 363 /* ========================================================================= */ 364 local void gf2_matrix_square(square, mat) 365 unsigned long *square; 366 unsigned long *mat; 367 { 368 int n; 369 370 for (n = 0; n < GF2_DIM; n++) 371 square[n] = gf2_matrix_times(mat, mat[n]); 372 } 373 374 /* ========================================================================= */ 375 uLong ZEXPORT crc32_combine(crc1, crc2, len2) 376 uLong crc1; 377 uLong crc2; 378 z_off_t len2; 379 { 380 int n; 381 unsigned long row; 382 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ 383 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ 384 385 /* degenerate case */ 386 if (len2 == 0) 387 return crc1; 388 389 /* put operator for one zero bit in odd */ 390 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */ 391 row = 1; 392 for (n = 1; n < GF2_DIM; n++) { 393 odd[n] = row; 394 row <<= 1; 395 } 396 397 /* put operator for two zero bits in even */ 398 gf2_matrix_square(even, odd); 399 400 /* put operator for four zero bits in odd */ 401 gf2_matrix_square(odd, even); 402 403 /* apply len2 zeros to crc1 (first square will put the operator for one 404 zero byte, eight zero bits, in even) */ 405 do { 406 /* apply zeros operator for this bit of len2 */ 407 gf2_matrix_square(even, odd); 408 if (len2 & 1) 409 crc1 = gf2_matrix_times(even, crc1); 410 len2 >>= 1; 411 412 /* if no more bits set, then done */ 413 if (len2 == 0) 414 break; 415 416 /* another iteration of the loop with odd and even swapped */ 417 gf2_matrix_square(odd, even); 418 if (len2 & 1) 419 crc1 = gf2_matrix_times(odd, crc1); 420 len2 >>= 1; 421 422 /* if no more bits set, then done */ 423 } while (len2 != 0); 424 425 /* return combined crc */ 426 crc1 ^= crc2; 427 return crc1; 428 } 429