1 /* $NetBSD: crc32.c,v 1.4 2006/02/18 18:39:58 dsl Exp $ */ 2 3 /* crc32.c -- compute the CRC-32 of a data stream 4 * Copyright (C) 1995-2005 Mark Adler 5 * For conditions of distribution and use, see copyright notice in zlib.h 6 * 7 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster 8 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing 9 * tables for updating the shift register in one step with three exclusive-ors 10 * instead of four steps with four exclusive-ors. This results in about a 11 * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. 12 */ 13 14 /* @(#) Id */ 15 16 /* 17 Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore 18 protection on the static variables used to control the first-use generation 19 of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should 20 first call get_crc_table() to initialize the tables before allowing more than 21 one thread to use crc32(). 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 #if defined(__NetBSD__) && defined(_STANDALONE) 36 #define NOBYFOUR 37 #define DYNAMIC_CRC_TABLE 38 #endif 39 40 /* Find a four-byte integer type for crc32_little() and crc32_big(). */ 41 #ifndef NOBYFOUR 42 #if defined(__NetBSD__) && defined(_KERNEL) 43 # define BYFOUR 44 typedef uint32_t u4; 45 #else 46 # ifdef STDC /* need ANSI C limits.h to determine sizes */ 47 # include <limits.h> 48 # define BYFOUR 49 # if (UINT_MAX == 0xffffffffUL) 50 typedef unsigned int u4; 51 # else 52 # if (ULONG_MAX == 0xffffffffUL) 53 typedef unsigned long u4; 54 # else 55 # if (USHRT_MAX == 0xffffffffUL) 56 typedef unsigned short u4; 57 # else 58 # undef BYFOUR /* can't find a four-byte integer type! */ 59 # endif 60 # endif 61 # endif 62 # endif /* STDC */ 63 #endif /* __NetBSD__ && _KERNEL */ 64 #endif /* !NOBYFOUR */ 65 66 /* Definitions for doing the crc four data bytes at a time. */ 67 #ifdef BYFOUR 68 # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ 69 (((w)&0xff00)<<8)+(((w)&0xff)<<24)) 70 local unsigned long crc32_little OF((unsigned long, 71 const unsigned char FAR *, unsigned)); 72 local unsigned long crc32_big OF((unsigned long, 73 const unsigned char FAR *, unsigned)); 74 # define TBLS 8 75 #else 76 # define TBLS 1 77 #endif /* BYFOUR */ 78 79 /* Local functions for crc concatenation */ 80 local unsigned long gf2_matrix_times OF((unsigned long *mat, 81 unsigned long vec)); 82 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); 83 84 #ifdef DYNAMIC_CRC_TABLE 85 86 local volatile int crc_table_empty = 1; 87 local unsigned long FAR crc_table[TBLS][256]; 88 local void make_crc_table OF((void)); 89 #ifdef MAKECRCH 90 local void write_table OF((FILE *, const unsigned long FAR *)); 91 #endif /* MAKECRCH */ 92 /* 93 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: 94 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. 95 96 Polynomials over GF(2) are represented in binary, one bit per coefficient, 97 with the lowest powers in the most significant bit. Then adding polynomials 98 is just exclusive-or, and multiplying a polynomial by x is a right shift by 99 one. If we call the above polynomial p, and represent a byte as the 100 polynomial q, also with the lowest power in the most significant bit (so the 101 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, 102 where a mod b means the remainder after dividing a by b. 103 104 This calculation is done using the shift-register method of multiplying and 105 taking the remainder. The register is initialized to zero, and for each 106 incoming bit, x^32 is added mod p to the register if the bit is a one (where 107 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by 108 x (which is shifting right by one and adding x^32 mod p if the bit shifted 109 out is a one). We start with the highest power (least significant bit) of 110 q and repeat for all eight bits of q. 111 112 The first table is simply the CRC of all possible eight bit values. This is 113 all the information needed to generate CRCs on data a byte at a time for all 114 combinations of CRC register values and incoming bytes. The remaining tables 115 allow for word-at-a-time CRC calculation for both big-endian and little- 116 endian machines, where a word is four bytes. 117 */ 118 local void make_crc_table() 119 { 120 unsigned long c; 121 int n, k; 122 unsigned long poly; /* polynomial exclusive-or pattern */ 123 /* terms of polynomial defining this crc (except x^32): */ 124 static volatile int first = 1; /* flag to limit concurrent making */ 125 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; 126 127 /* See if another task is already doing this (not thread-safe, but better 128 than nothing -- significantly reduces duration of vulnerability in 129 case the advice about DYNAMIC_CRC_TABLE is ignored) */ 130 if (first) { 131 first = 0; 132 133 /* make exclusive-or pattern from polynomial (0xedb88320UL) */ 134 poly = 0UL; 135 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) 136 poly |= 1UL << (31 - p[n]); 137 138 /* generate a crc for every 8-bit value */ 139 for (n = 0; n < 256; n++) { 140 c = (unsigned long)n; 141 for (k = 0; k < 8; k++) 142 c = c & 1 ? poly ^ (c >> 1) : c >> 1; 143 crc_table[0][n] = c; 144 } 145 146 #ifdef BYFOUR 147 /* generate crc for each value followed by one, two, and three zeros, 148 and then the byte reversal of those as well as the first table */ 149 for (n = 0; n < 256; n++) { 150 c = crc_table[0][n]; 151 crc_table[4][n] = REV(c); 152 for (k = 1; k < 4; k++) { 153 c = crc_table[0][c & 0xff] ^ (c >> 8); 154 crc_table[k][n] = c; 155 crc_table[k + 4][n] = REV(c); 156 } 157 } 158 #endif /* BYFOUR */ 159 160 crc_table_empty = 0; 161 } 162 else { /* not first */ 163 /* wait for the other guy to finish (not efficient, but rare) */ 164 while (crc_table_empty) 165 ; 166 } 167 168 #ifdef MAKECRCH 169 /* write out CRC tables to crc32.h */ 170 { 171 FILE *out; 172 173 out = fopen("crc32.h", "w"); 174 if (out == NULL) return; 175 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); 176 fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); 177 fprintf(out, "local const unsigned long FAR "); 178 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); 179 write_table(out, crc_table[0]); 180 # ifdef BYFOUR 181 fprintf(out, "#ifdef BYFOUR\n"); 182 for (k = 1; k < 8; k++) { 183 fprintf(out, " },\n {\n"); 184 write_table(out, crc_table[k]); 185 } 186 fprintf(out, "#endif\n"); 187 # endif /* BYFOUR */ 188 fprintf(out, " }\n};\n"); 189 fclose(out); 190 } 191 #endif /* MAKECRCH */ 192 } 193 194 #ifdef MAKECRCH 195 local void write_table(out, table) 196 FILE *out; 197 const unsigned long FAR *table; 198 { 199 int n; 200 201 for (n = 0; n < 256; n++) 202 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n], 203 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); 204 } 205 #endif /* MAKECRCH */ 206 207 #else /* !DYNAMIC_CRC_TABLE */ 208 /* ======================================================================== 209 * Tables of CRC-32s of all single-byte values, made by make_crc_table(). 210 */ 211 #include "crc32.h" 212 #endif /* DYNAMIC_CRC_TABLE */ 213 214 /* ========================================================================= 215 * This function can be used by asm versions of crc32() 216 */ 217 const unsigned long FAR * ZEXPORT get_crc_table() 218 { 219 #ifdef DYNAMIC_CRC_TABLE 220 if (crc_table_empty) 221 make_crc_table(); 222 #endif /* DYNAMIC_CRC_TABLE */ 223 return (const unsigned long FAR *)crc_table; 224 } 225 226 /* ========================================================================= */ 227 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) 228 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 229 230 /* ========================================================================= */ 231 unsigned long ZEXPORT crc32(crc, buf, len) 232 unsigned long crc; 233 const unsigned char FAR *buf; 234 unsigned len; 235 { 236 if (buf == Z_NULL) return 0UL; 237 238 #ifdef DYNAMIC_CRC_TABLE 239 if (crc_table_empty) 240 make_crc_table(); 241 #endif /* DYNAMIC_CRC_TABLE */ 242 243 #ifdef BYFOUR 244 if (sizeof(void *) == sizeof(z_ptrdiff_t)) { 245 u4 endian; 246 247 endian = 1; 248 if (*((unsigned char *)(&endian))) 249 return crc32_little(crc, buf, len); 250 else 251 return crc32_big(crc, buf, len); 252 } 253 #endif /* BYFOUR */ 254 crc = crc ^ 0xffffffffUL; 255 while (len >= 8) { 256 DO8; 257 len -= 8; 258 } 259 if (len) do { 260 DO1; 261 } while (--len); 262 return crc ^ 0xffffffffUL; 263 } 264 265 #ifdef BYFOUR 266 267 /* ========================================================================= */ 268 #define DOLIT4 c ^= *buf4++; \ 269 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ 270 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] 271 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 272 273 /* ========================================================================= */ 274 local unsigned long crc32_little(crc, buf, len) 275 unsigned long crc; 276 const unsigned char FAR *buf; 277 unsigned len; 278 { 279 register u4 c; 280 register const u4 FAR *buf4; 281 282 c = (u4)crc; 283 c = ~c; 284 while (len && ((z_ptrdiff_t)buf & 3)) { 285 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 286 len--; 287 } 288 289 buf4 = (const u4 FAR *)(const void FAR *)buf; 290 while (len >= 32) { 291 DOLIT32; 292 len -= 32; 293 } 294 while (len >= 4) { 295 DOLIT4; 296 len -= 4; 297 } 298 buf = (const unsigned char FAR *)buf4; 299 300 if (len) do { 301 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 302 } while (--len); 303 c = ~c; 304 return (unsigned long)c; 305 } 306 307 /* ========================================================================= */ 308 #define DOBIG4 c ^= *++buf4; \ 309 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ 310 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] 311 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 312 313 /* ========================================================================= */ 314 local unsigned long crc32_big(crc, buf, len) 315 unsigned long crc; 316 const unsigned char FAR *buf; 317 unsigned len; 318 { 319 register u4 c; 320 register const u4 FAR *buf4; 321 322 c = REV((u4)crc); 323 c = ~c; 324 while (len && ((z_ptrdiff_t)buf & 3)) { 325 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 326 len--; 327 } 328 329 buf4 = (const u4 FAR *)(const void FAR *)buf; 330 buf4--; 331 while (len >= 32) { 332 DOBIG32; 333 len -= 32; 334 } 335 while (len >= 4) { 336 DOBIG4; 337 len -= 4; 338 } 339 buf4++; 340 buf = (const unsigned char FAR *)buf4; 341 342 if (len) do { 343 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 344 } while (--len); 345 c = ~c; 346 return (unsigned long)(REV(c)); 347 } 348 349 #endif /* BYFOUR */ 350 351 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ 352 353 /* ========================================================================= */ 354 local unsigned long gf2_matrix_times(mat, vec) 355 unsigned long *mat; 356 unsigned long vec; 357 { 358 unsigned long sum; 359 360 sum = 0; 361 while (vec) { 362 if (vec & 1) 363 sum ^= *mat; 364 vec >>= 1; 365 mat++; 366 } 367 return sum; 368 } 369 370 /* ========================================================================= */ 371 local void gf2_matrix_square(square, mat) 372 unsigned long *square; 373 unsigned long *mat; 374 { 375 int n; 376 377 for (n = 0; n < GF2_DIM; n++) 378 square[n] = gf2_matrix_times(mat, mat[n]); 379 } 380 381 /* ========================================================================= */ 382 uLong ZEXPORT crc32_combine(crc1, crc2, len2) 383 uLong crc1; 384 uLong crc2; 385 z_off_t len2; 386 { 387 int n; 388 unsigned long row; 389 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ 390 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ 391 392 /* degenerate case */ 393 if (len2 == 0) 394 return crc1; 395 396 /* put operator for one zero bit in odd */ 397 odd[0] = 0xedb88320L; /* CRC-32 polynomial */ 398 row = 1; 399 for (n = 1; n < GF2_DIM; n++) { 400 odd[n] = row; 401 row <<= 1; 402 } 403 404 /* put operator for two zero bits in even */ 405 gf2_matrix_square(even, odd); 406 407 /* put operator for four zero bits in odd */ 408 gf2_matrix_square(odd, even); 409 410 /* apply len2 zeros to crc1 (first square will put the operator for one 411 zero byte, eight zero bits, in even) */ 412 do { 413 /* apply zeros operator for this bit of len2 */ 414 gf2_matrix_square(even, odd); 415 if (len2 & 1) 416 crc1 = gf2_matrix_times(even, crc1); 417 len2 >>= 1; 418 419 /* if no more bits set, then done */ 420 if (len2 == 0) 421 break; 422 423 /* another iteration of the loop with odd and even swapped */ 424 gf2_matrix_square(odd, even); 425 if (len2 & 1) 426 crc1 = gf2_matrix_times(odd, crc1); 427 len2 >>= 1; 428 429 /* if no more bits set, then done */ 430 } while (len2 != 0); 431 432 /* return combined crc */ 433 crc1 ^= crc2; 434 return crc1; 435 } 436