1 /* $OpenBSD: crc32.c,v 1.12 2011/07/07 02:57:24 deraadt Exp $ */ 2 /* crc32.c -- compute the CRC-32 of a data stream 3 * Copyright (C) 1995-2005 Mark Adler 4 * For conditions of distribution and use, see copyright notice in zlib.h 5 * 6 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster 7 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing 8 * tables for updating the shift register in one step with three exclusive-ors 9 * instead of four steps with four exclusive-ors. This results in about a 10 * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. 11 */ 12 13 /* 14 Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore 15 protection on the static variables used to control the first-use generation 16 of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should 17 first call get_crc_table() to initialize the tables before allowing more than 18 one thread to use crc32(). 19 */ 20 21 #ifdef MAKECRCH 22 # include <stdio.h> 23 # ifndef DYNAMIC_CRC_TABLE 24 # define DYNAMIC_CRC_TABLE 25 # endif /* !DYNAMIC_CRC_TABLE */ 26 #endif /* MAKECRCH */ 27 28 #include "zutil.h" /* for STDC and FAR definitions */ 29 30 #define local static 31 32 #ifndef _KERNEL 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 #endif 54 55 /* Definitions for doing the crc four data bytes at a time. */ 56 #ifdef BYFOUR 57 # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ 58 (((w)&0xff00)<<8)+(((w)&0xff)<<24)) 59 local unsigned long crc32_little OF((unsigned long, 60 const unsigned char FAR *, unsigned)); 61 local unsigned long crc32_big OF((unsigned long, 62 const unsigned char FAR *, unsigned)); 63 # define TBLS 8 64 #else 65 # define TBLS 1 66 #endif /* BYFOUR */ 67 68 /* Local functions for crc concatenation */ 69 local unsigned long gf2_matrix_times OF((unsigned long *mat, 70 unsigned long vec)); 71 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); 72 73 #ifdef DYNAMIC_CRC_TABLE 74 75 local volatile int crc_table_empty = 1; 76 local unsigned long FAR crc_table[TBLS][256]; 77 local void make_crc_table OF((void)); 78 #ifdef MAKECRCH 79 local void write_table OF((FILE *, const unsigned long FAR *)); 80 #endif /* MAKECRCH */ 81 /* 82 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: 83 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. 84 85 Polynomials over GF(2) are represented in binary, one bit per coefficient, 86 with the lowest powers in the most significant bit. Then adding polynomials 87 is just exclusive-or, and multiplying a polynomial by x is a right shift by 88 one. If we call the above polynomial p, and represent a byte as the 89 polynomial q, also with the lowest power in the most significant bit (so the 90 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, 91 where a mod b means the remainder after dividing a by b. 92 93 This calculation is done using the shift-register method of multiplying and 94 taking the remainder. The register is initialized to zero, and for each 95 incoming bit, x^32 is added mod p to the register if the bit is a one (where 96 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by 97 x (which is shifting right by one and adding x^32 mod p if the bit shifted 98 out is a one). We start with the highest power (least significant bit) of 99 q and repeat for all eight bits of q. 100 101 The first table is simply the CRC of all possible eight bit values. This is 102 all the information needed to generate CRCs on data a byte at a time for all 103 combinations of CRC register values and incoming bytes. The remaining tables 104 allow for word-at-a-time CRC calculation for both big-endian and little- 105 endian machines, where a word is four bytes. 106 */ 107 local void make_crc_table() 108 { 109 unsigned long c; 110 int n, k; 111 unsigned long poly; /* polynomial exclusive-or pattern */ 112 /* terms of polynomial defining this crc (except x^32): */ 113 static volatile int first = 1; /* flag to limit concurrent making */ 114 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; 115 116 /* See if another task is already doing this (not thread-safe, but better 117 than nothing -- significantly reduces duration of vulnerability in 118 case the advice about DYNAMIC_CRC_TABLE is ignored) */ 119 if (first) { 120 first = 0; 121 122 /* make exclusive-or pattern from polynomial (0xedb88320UL) */ 123 poly = 0UL; 124 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) 125 poly |= 1UL << (31 - p[n]); 126 127 /* generate a crc for every 8-bit value */ 128 for (n = 0; n < 256; n++) { 129 c = (unsigned long)n; 130 for (k = 0; k < 8; k++) 131 c = c & 1 ? poly ^ (c >> 1) : c >> 1; 132 crc_table[0][n] = c; 133 } 134 135 #ifdef BYFOUR 136 /* generate crc for each value followed by one, two, and three zeros, 137 and then the byte reversal of those as well as the first table */ 138 for (n = 0; n < 256; n++) { 139 c = crc_table[0][n]; 140 crc_table[4][n] = REV(c); 141 for (k = 1; k < 4; k++) { 142 c = crc_table[0][c & 0xff] ^ (c >> 8); 143 crc_table[k][n] = c; 144 crc_table[k + 4][n] = REV(c); 145 } 146 } 147 #endif /* BYFOUR */ 148 149 crc_table_empty = 0; 150 } 151 else { /* not first */ 152 /* wait for the other guy to finish (not efficient, but rare) */ 153 while (crc_table_empty) 154 ; 155 } 156 157 #ifdef MAKECRCH 158 /* write out CRC tables to crc32.h */ 159 { 160 FILE *out; 161 162 out = fopen("crc32.h", "w"); 163 if (out == NULL) return; 164 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); 165 fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); 166 fprintf(out, "local const unsigned long FAR "); 167 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); 168 write_table(out, crc_table[0]); 169 # ifdef BYFOUR 170 fprintf(out, "#ifdef BYFOUR\n"); 171 for (k = 1; k < 8; k++) { 172 fprintf(out, " },\n {\n"); 173 write_table(out, crc_table[k]); 174 } 175 fprintf(out, "#endif\n"); 176 # endif /* BYFOUR */ 177 fprintf(out, " }\n};\n"); 178 fclose(out); 179 } 180 #endif /* MAKECRCH */ 181 } 182 183 #ifdef MAKECRCH 184 local void write_table(out, table) 185 FILE *out; 186 const unsigned long FAR *table; 187 { 188 int n; 189 190 for (n = 0; n < 256; n++) 191 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n], 192 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); 193 } 194 #endif /* MAKECRCH */ 195 196 #else /* !DYNAMIC_CRC_TABLE */ 197 /* ======================================================================== 198 * Tables of CRC-32s of all single-byte values, made by make_crc_table(). 199 */ 200 #include "crc32.h" 201 #endif /* DYNAMIC_CRC_TABLE */ 202 203 /* ========================================================================= 204 * This function can be used by asm versions of crc32() 205 */ 206 const unsigned long FAR * ZEXPORT get_crc_table() 207 { 208 #ifdef DYNAMIC_CRC_TABLE 209 if (crc_table_empty) 210 make_crc_table(); 211 #endif /* DYNAMIC_CRC_TABLE */ 212 return (const unsigned long FAR *)crc_table; 213 } 214 215 /* ========================================================================= */ 216 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) 217 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 218 219 /* ========================================================================= */ 220 unsigned long ZEXPORT crc32(crc, buf, len) 221 unsigned long crc; 222 const unsigned char FAR *buf; 223 unsigned len; 224 { 225 if (buf == Z_NULL) return 0UL; 226 227 #ifdef DYNAMIC_CRC_TABLE 228 if (crc_table_empty) 229 make_crc_table(); 230 #endif /* DYNAMIC_CRC_TABLE */ 231 232 #ifdef BYFOUR 233 if (sizeof(void *) == sizeof(ptrdiff_t)) { 234 u4 endian; 235 236 endian = 1; 237 if (*((unsigned char *)(&endian))) 238 return crc32_little(crc, buf, len); 239 else 240 return crc32_big(crc, buf, len); 241 } 242 #endif /* BYFOUR */ 243 crc = crc ^ 0xffffffffUL; 244 while (len >= 8) { 245 DO8; 246 len -= 8; 247 } 248 if (len) do { 249 DO1; 250 } while (--len); 251 return crc ^ 0xffffffffUL; 252 } 253 254 #ifdef BYFOUR 255 256 /* ========================================================================= */ 257 #define DOLIT4 c ^= *buf4++; \ 258 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ 259 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] 260 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 261 262 /* ========================================================================= */ 263 local unsigned long crc32_little(crc, buf, len) 264 unsigned long crc; 265 const unsigned char FAR *buf; 266 unsigned len; 267 { 268 register u4 c; 269 register const u4 FAR *buf4; 270 271 c = (u4)crc; 272 c = ~c; 273 while (len && ((ptrdiff_t)buf & 3)) { 274 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 275 len--; 276 } 277 278 buf4 = (const u4 FAR *)(const void FAR *)buf; 279 while (len >= 32) { 280 DOLIT32; 281 len -= 32; 282 } 283 while (len >= 4) { 284 DOLIT4; 285 len -= 4; 286 } 287 buf = (const unsigned char FAR *)buf4; 288 289 if (len) do { 290 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 291 } while (--len); 292 c = ~c; 293 return (unsigned long)c; 294 } 295 296 /* ========================================================================= */ 297 #define DOBIG4 c ^= *++buf4; \ 298 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ 299 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] 300 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 301 302 /* ========================================================================= */ 303 local unsigned long crc32_big(crc, buf, len) 304 unsigned long crc; 305 const unsigned char FAR *buf; 306 unsigned len; 307 { 308 register u4 c; 309 register const u4 FAR *buf4; 310 311 c = REV((u4)crc); 312 c = ~c; 313 while (len && ((ptrdiff_t)buf & 3)) { 314 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 315 len--; 316 } 317 318 buf4 = (const u4 FAR *)(const void FAR *)buf; 319 buf4--; 320 while (len >= 32) { 321 DOBIG32; 322 len -= 32; 323 } 324 while (len >= 4) { 325 DOBIG4; 326 len -= 4; 327 } 328 buf4++; 329 buf = (const unsigned char FAR *)buf4; 330 331 if (len) do { 332 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 333 } while (--len); 334 c = ~c; 335 return (unsigned long)(REV(c)); 336 } 337 338 #endif /* BYFOUR */ 339 340 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ 341 342 /* ========================================================================= */ 343 local unsigned long gf2_matrix_times(mat, vec) 344 unsigned long *mat; 345 unsigned long vec; 346 { 347 unsigned long sum; 348 349 sum = 0; 350 while (vec) { 351 if (vec & 1) 352 sum ^= *mat; 353 vec >>= 1; 354 mat++; 355 } 356 return sum; 357 } 358 359 /* ========================================================================= */ 360 local void gf2_matrix_square(square, mat) 361 unsigned long *square; 362 unsigned long *mat; 363 { 364 int n; 365 366 for (n = 0; n < GF2_DIM; n++) 367 square[n] = gf2_matrix_times(mat, mat[n]); 368 } 369 370 /* ========================================================================= */ 371 uLong ZEXPORT crc32_combine(crc1, crc2, len2) 372 uLong crc1; 373 uLong crc2; 374 z_off_t len2; 375 { 376 int n; 377 unsigned long row; 378 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ 379 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ 380 381 /* degenerate case */ 382 if (len2 == 0) 383 return crc1; 384 385 /* put operator for one zero bit in odd */ 386 odd[0] = 0xedb88320L; /* CRC-32 polynomial */ 387 row = 1; 388 for (n = 1; n < GF2_DIM; n++) { 389 odd[n] = row; 390 row <<= 1; 391 } 392 393 /* put operator for two zero bits in even */ 394 gf2_matrix_square(even, odd); 395 396 /* put operator for four zero bits in odd */ 397 gf2_matrix_square(odd, even); 398 399 /* apply len2 zeros to crc1 (first square will put the operator for one 400 zero byte, eight zero bits, in even) */ 401 do { 402 /* apply zeros operator for this bit of len2 */ 403 gf2_matrix_square(even, odd); 404 if (len2 & 1) 405 crc1 = gf2_matrix_times(even, crc1); 406 len2 >>= 1; 407 408 /* if no more bits set, then done */ 409 if (len2 == 0) 410 break; 411 412 /* another iteration of the loop with odd and even swapped */ 413 gf2_matrix_square(odd, even); 414 if (len2 & 1) 415 crc1 = gf2_matrix_times(odd, crc1); 416 len2 >>= 1; 417 418 /* if no more bits set, then done */ 419 } while (len2 != 0); 420 421 /* return combined crc */ 422 crc1 ^= crc2; 423 return crc1; 424 } 425