1 /* $NetBSD: crc32.c,v 1.3 2006/01/25 23:15:55 uwe 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 /* Find a four-byte integer type for crc32_little() and crc32_big(). */ 36 #ifndef NOBYFOUR 37 #if defined(__NetBSD__) && (defined(_KERNEL) || defined(_STANDALONE)) 38 # define BYFOUR 39 typedef uint32_t u4; 40 #else 41 # ifdef STDC /* need ANSI C limits.h to determine sizes */ 42 # include <limits.h> 43 # define BYFOUR 44 # if (UINT_MAX == 0xffffffffUL) 45 typedef unsigned int u4; 46 # else 47 # if (ULONG_MAX == 0xffffffffUL) 48 typedef unsigned long u4; 49 # else 50 # if (USHRT_MAX == 0xffffffffUL) 51 typedef unsigned short u4; 52 # else 53 # undef BYFOUR /* can't find a four-byte integer type! */ 54 # endif 55 # endif 56 # endif 57 # endif /* STDC */ 58 #endif /* __NetBSD__ && (_KERNEL || _STANDALONE) */ 59 #endif /* !NOBYFOUR */ 60 61 /* Definitions for doing the crc four data bytes at a time. */ 62 #ifdef BYFOUR 63 # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ 64 (((w)&0xff00)<<8)+(((w)&0xff)<<24)) 65 local unsigned long crc32_little OF((unsigned long, 66 const unsigned char FAR *, unsigned)); 67 local unsigned long crc32_big OF((unsigned long, 68 const unsigned char FAR *, unsigned)); 69 # define TBLS 8 70 #else 71 # define TBLS 1 72 #endif /* BYFOUR */ 73 74 /* Local functions for crc concatenation */ 75 local unsigned long gf2_matrix_times OF((unsigned long *mat, 76 unsigned long vec)); 77 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); 78 79 #ifdef DYNAMIC_CRC_TABLE 80 81 local volatile int crc_table_empty = 1; 82 local unsigned long FAR crc_table[TBLS][256]; 83 local void make_crc_table OF((void)); 84 #ifdef MAKECRCH 85 local void write_table OF((FILE *, const unsigned long FAR *)); 86 #endif /* MAKECRCH */ 87 /* 88 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: 89 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. 90 91 Polynomials over GF(2) are represented in binary, one bit per coefficient, 92 with the lowest powers in the most significant bit. Then adding polynomials 93 is just exclusive-or, and multiplying a polynomial by x is a right shift by 94 one. If we call the above polynomial p, and represent a byte as the 95 polynomial q, also with the lowest power in the most significant bit (so the 96 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, 97 where a mod b means the remainder after dividing a by b. 98 99 This calculation is done using the shift-register method of multiplying and 100 taking the remainder. The register is initialized to zero, and for each 101 incoming bit, x^32 is added mod p to the register if the bit is a one (where 102 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by 103 x (which is shifting right by one and adding x^32 mod p if the bit shifted 104 out is a one). We start with the highest power (least significant bit) of 105 q and repeat for all eight bits of q. 106 107 The first table is simply the CRC of all possible eight bit values. This is 108 all the information needed to generate CRCs on data a byte at a time for all 109 combinations of CRC register values and incoming bytes. The remaining tables 110 allow for word-at-a-time CRC calculation for both big-endian and little- 111 endian machines, where a word is four bytes. 112 */ 113 local void make_crc_table() 114 { 115 unsigned long c; 116 int n, k; 117 unsigned long poly; /* polynomial exclusive-or pattern */ 118 /* terms of polynomial defining this crc (except x^32): */ 119 static volatile int first = 1; /* flag to limit concurrent making */ 120 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; 121 122 /* See if another task is already doing this (not thread-safe, but better 123 than nothing -- significantly reduces duration of vulnerability in 124 case the advice about DYNAMIC_CRC_TABLE is ignored) */ 125 if (first) { 126 first = 0; 127 128 /* make exclusive-or pattern from polynomial (0xedb88320UL) */ 129 poly = 0UL; 130 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) 131 poly |= 1UL << (31 - p[n]); 132 133 /* generate a crc for every 8-bit value */ 134 for (n = 0; n < 256; n++) { 135 c = (unsigned long)n; 136 for (k = 0; k < 8; k++) 137 c = c & 1 ? poly ^ (c >> 1) : c >> 1; 138 crc_table[0][n] = c; 139 } 140 141 #ifdef BYFOUR 142 /* generate crc for each value followed by one, two, and three zeros, 143 and then the byte reversal of those as well as the first table */ 144 for (n = 0; n < 256; n++) { 145 c = crc_table[0][n]; 146 crc_table[4][n] = REV(c); 147 for (k = 1; k < 4; k++) { 148 c = crc_table[0][c & 0xff] ^ (c >> 8); 149 crc_table[k][n] = c; 150 crc_table[k + 4][n] = REV(c); 151 } 152 } 153 #endif /* BYFOUR */ 154 155 crc_table_empty = 0; 156 } 157 else { /* not first */ 158 /* wait for the other guy to finish (not efficient, but rare) */ 159 while (crc_table_empty) 160 ; 161 } 162 163 #ifdef MAKECRCH 164 /* write out CRC tables to crc32.h */ 165 { 166 FILE *out; 167 168 out = fopen("crc32.h", "w"); 169 if (out == NULL) return; 170 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); 171 fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); 172 fprintf(out, "local const unsigned long FAR "); 173 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); 174 write_table(out, crc_table[0]); 175 # ifdef BYFOUR 176 fprintf(out, "#ifdef BYFOUR\n"); 177 for (k = 1; k < 8; k++) { 178 fprintf(out, " },\n {\n"); 179 write_table(out, crc_table[k]); 180 } 181 fprintf(out, "#endif\n"); 182 # endif /* BYFOUR */ 183 fprintf(out, " }\n};\n"); 184 fclose(out); 185 } 186 #endif /* MAKECRCH */ 187 } 188 189 #ifdef MAKECRCH 190 local void write_table(out, table) 191 FILE *out; 192 const unsigned long FAR *table; 193 { 194 int n; 195 196 for (n = 0; n < 256; n++) 197 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", 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 unsigned 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(z_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 && ((z_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 && ((z_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 uLong ZEXPORT crc32_combine(crc1, crc2, len2) 378 uLong crc1; 379 uLong crc2; 380 z_off_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 */ 388 if (len2 == 0) 389 return crc1; 390 391 /* put operator for one zero bit in odd */ 392 odd[0] = 0xedb88320L; /* 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