crc32.c revision 180208
175752Smsmith/* crc32.c -- compute the CRC-32 of a data stream 275752Smsmith * Copyright (C) 1995-2005 Mark Adler 375752Smsmith * For conditions of distribution and use, see copyright notice in zlib.h 475752Smsmith * 575752Smsmith * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster 675752Smsmith * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing 775752Smsmith * tables for updating the shift register in one step with three exclusive-ors 875752Smsmith * instead of four steps with four exclusive-ors. This results in about a 975752Smsmith * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. 1075752Smsmith */ 1175752Smsmith 1275752Smsmith/* @(#) $Id$ */ 1375752Smsmith 1475752Smsmith/* 1575752Smsmith Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore 1675752Smsmith protection on the static variables used to control the first-use generation 1775752Smsmith of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should 1875752Smsmith first call get_crc_table() to initialize the tables before allowing more than 1975752Smsmith one thread to use crc32(). 2075752Smsmith */ 2175752Smsmith 2275752Smsmith#ifdef MAKECRCH 2375752Smsmith# include <stdio.h> 2475752Smsmith# ifndef DYNAMIC_CRC_TABLE 2575752Smsmith# define DYNAMIC_CRC_TABLE 2675752Smsmith# endif /* !DYNAMIC_CRC_TABLE */ 2775752Smsmith#endif /* MAKECRCH */ 2875752Smsmith 2975752Smsmith#include "zutil.h" /* for STDC and FAR definitions */ 3075752Smsmith 3175752Smsmith#define local static 32124128Scharnier 33124128Scharnier/* Find a four-byte integer type for crc32_little() and crc32_big(). */ 34124128Scharnier#ifndef NOBYFOUR 3575752Smsmith# ifdef STDC /* need ANSI C limits.h to determine sizes */ 3675752Smsmith# include <limits.h> 3775752Smsmith# define BYFOUR 38162799Sru# if (UINT_MAX == 0xffffffffUL) 3975752Smsmith typedef unsigned int u4; 4075752Smsmith# else 4175752Smsmith# if (ULONG_MAX == 0xffffffffUL) 4275752Smsmith typedef unsigned long u4; 43103663Simp# else 4475752Smsmith# if (USHRT_MAX == 0xffffffffUL) 4587553Smikeh typedef unsigned short u4; 4687553Smikeh# else 4787553Smikeh# undef BYFOUR /* can't find a four-byte integer type! */ 4887553Smikeh# endif 4987553Smikeh# endif 5087553Smikeh# endif 5187553Smikeh# endif /* STDC */ 5275752Smsmith#endif /* !NOBYFOUR */ 5375752Smsmith 5475752Smsmith/* Definitions for doing the crc four data bytes at a time. */ 5575752Smsmith#ifdef BYFOUR 5675752Smsmith# define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ 5775752Smsmith (((w)&0xff00)<<8)+(((w)&0xff)<<24)) 5875752Smsmith local unsigned long crc32_little OF((unsigned long, 5975752Smsmith const unsigned char FAR *, unsigned)); 6075752Smsmith local unsigned long crc32_big OF((unsigned long, 6175752Smsmith const unsigned char FAR *, unsigned)); 6275752Smsmith# define TBLS 8 6375752Smsmith#else 6475752Smsmith# define TBLS 1 6575752Smsmith#endif /* BYFOUR */ 6675752Smsmith 6775752Smsmith/* Local functions for crc concatenation */ 68173057Sjhblocal unsigned long gf2_matrix_times OF((unsigned long *mat, 6975752Smsmith unsigned long vec)); 7075752Smsmithlocal void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); 7175752Smsmith 7275752Smsmith#ifdef DYNAMIC_CRC_TABLE 7375752Smsmith 7475752Smsmithlocal volatile int crc_table_empty = 1; 7575752Smsmithlocal unsigned long FAR crc_table[TBLS][256]; 7675752Smsmithlocal void make_crc_table OF((void)); 7775752Smsmith#ifdef MAKECRCH 7875752Smsmith local void write_table OF((FILE *, const unsigned long FAR *)); 7975752Smsmith#endif /* MAKECRCH */ 8075752Smsmith/* 8175752Smsmith Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: 8275752Smsmith 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. 8375752Smsmith 8475752Smsmith Polynomials over GF(2) are represented in binary, one bit per coefficient, 8575752Smsmith with the lowest powers in the most significant bit. Then adding polynomials 8675752Smsmith is just exclusive-or, and multiplying a polynomial by x is a right shift by 8775752Smsmith one. If we call the above polynomial p, and represent a byte as the 8875752Smsmith polynomial q, also with the lowest power in the most significant bit (so the 8975752Smsmith byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, 9075752Smsmith where a mod b means the remainder after dividing a by b. 9175752Smsmith 9275752Smsmith This calculation is done using the shift-register method of multiplying and 9375752Smsmith taking the remainder. The register is initialized to zero, and for each 9475752Smsmith incoming bit, x^32 is added mod p to the register if the bit is a one (where 9575752Smsmith x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by 9675752Smsmith x (which is shifting right by one and adding x^32 mod p if the bit shifted 9775752Smsmith out is a one). We start with the highest power (least significant bit) of 9875752Smsmith q and repeat for all eight bits of q. 9975752Smsmith 10075752Smsmith The first table is simply the CRC of all possible eight bit values. This is 10175752Smsmith all the information needed to generate CRCs on data a byte at a time for all 10275752Smsmith combinations of CRC register values and incoming bytes. The remaining tables 10375752Smsmith allow for word-at-a-time CRC calculation for both big-endian and little- 10475752Smsmith endian machines, where a word is four bytes. 10575752Smsmith*/ 10675752Smsmithlocal void make_crc_table() 10775752Smsmith{ 10875752Smsmith unsigned long c; 10975752Smsmith int n, k; 11075752Smsmith unsigned long poly; /* polynomial exclusive-or pattern */ 11175752Smsmith /* terms of polynomial defining this crc (except x^32): */ 11275752Smsmith static volatile int first = 1; /* flag to limit concurrent making */ 11375752Smsmith static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; 11475752Smsmith 11575752Smsmith /* See if another task is already doing this (not thread-safe, but better 11675752Smsmith than nothing -- significantly reduces duration of vulnerability in 11775752Smsmith case the advice about DYNAMIC_CRC_TABLE is ignored) */ 11875752Smsmith if (first) { 11975752Smsmith first = 0; 12075752Smsmith 12175752Smsmith /* make exclusive-or pattern from polynomial (0xedb88320UL) */ 12275752Smsmith poly = 0UL; 12375752Smsmith for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) 12475752Smsmith poly |= 1UL << (31 - p[n]); 12575752Smsmith 12675752Smsmith /* generate a crc for every 8-bit value */ 12775752Smsmith for (n = 0; n < 256; n++) { 12875752Smsmith c = (unsigned long)n; 12975752Smsmith for (k = 0; k < 8; k++) 13075752Smsmith c = c & 1 ? poly ^ (c >> 1) : c >> 1; 13175752Smsmith crc_table[0][n] = c; 13275752Smsmith } 13375752Smsmith 13475752Smsmith#ifdef BYFOUR 13575752Smsmith /* generate crc for each value followed by one, two, and three zeros, 13675752Smsmith and then the byte reversal of those as well as the first table */ 13775752Smsmith for (n = 0; n < 256; n++) { 13875752Smsmith c = crc_table[0][n]; 13975752Smsmith crc_table[4][n] = REV(c); 140199291Sattilio for (k = 1; k < 4; k++) { 14187553Smikeh c = crc_table[0][c & 0xff] ^ (c >> 8); 14275752Smsmith crc_table[k][n] = c; 14375752Smsmith crc_table[k + 4][n] = REV(c); 144111046Simp } 145111046Simp } 146111046Simp#endif /* BYFOUR */ 147111046Simp 148111046Simp crc_table_empty = 0; 149111046Simp } 15075752Smsmith else { /* not first */ 15175752Smsmith /* wait for the other guy to finish (not efficient, but rare) */ 15275752Smsmith while (crc_table_empty) 15375752Smsmith ; 15475752Smsmith } 15575752Smsmith 15675752Smsmith#ifdef MAKECRCH 15775752Smsmith /* write out CRC tables to crc32.h */ 15875752Smsmith { 15987553Smikeh FILE *out; 16075752Smsmith 16175752Smsmith out = fopen("crc32.h", "w"); 16275752Smsmith if (out == NULL) return; 16375752Smsmith fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); 16475752Smsmith fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); 16575752Smsmith fprintf(out, "local const unsigned long FAR "); 16687553Smikeh fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); 16775752Smsmith write_table(out, crc_table[0]); 16875752Smsmith# ifdef BYFOUR 16975752Smsmith fprintf(out, "#ifdef BYFOUR\n"); 17075752Smsmith for (k = 1; k < 8; k++) { 17175752Smsmith fprintf(out, " },\n {\n"); 17275752Smsmith write_table(out, crc_table[k]); 17375752Smsmith } 17475752Smsmith fprintf(out, "#endif\n"); 17575752Smsmith# endif /* BYFOUR */ 17675752Smsmith fprintf(out, " }\n};\n"); 17775752Smsmith fclose(out); 17875752Smsmith } 17975752Smsmith#endif /* MAKECRCH */ 18075752Smsmith} 18175752Smsmith 18275752Smsmith#ifdef MAKECRCH 18375752Smsmithlocal void write_table(out, table) 18475752Smsmith FILE *out; 18575752Smsmith const unsigned long FAR *table; 18687553Smikeh{ 18775752Smsmith int n; 18875752Smsmith 18975752Smsmith for (n = 0; n < 256; n++) 19075752Smsmith fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n], 19175752Smsmith n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); 19275752Smsmith} 19375752Smsmith#endif /* MAKECRCH */ 19475752Smsmith 19575752Smsmith#else /* !DYNAMIC_CRC_TABLE */ 19675752Smsmith/* ======================================================================== 19775752Smsmith * Tables of CRC-32s of all single-byte values, made by make_crc_table(). 19875752Smsmith */ 19975752Smsmith#include "crc32.h" 200103663Simp#endif /* DYNAMIC_CRC_TABLE */ 20175752Smsmith 20275752Smsmith/* ========================================================================= 20375752Smsmith * This function can be used by asm versions of crc32() 20475752Smsmith */ 20575752Smsmithconst unsigned long FAR * ZEXPORT get_crc_table() 20675752Smsmith{ 20775752Smsmith#ifdef DYNAMIC_CRC_TABLE 208103663Simp if (crc_table_empty) 209103663Simp make_crc_table(); 210103663Simp#endif /* DYNAMIC_CRC_TABLE */ 21175752Smsmith return (const unsigned long FAR *)crc_table; 212162799Sru} 213162799Sru 214162799Sru/* ========================================================================= */ 215162799Sru#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) 21675752Smsmith#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 21775752Smsmith 21875752Smsmith/* ========================================================================= */ 21975752Smsmithunsigned long ZEXPORT crc32(crc, buf, len) 22075752Smsmith unsigned long crc; 22175752Smsmith const unsigned char FAR *buf; 22275752Smsmith unsigned len; 22375752Smsmith{ 22475752Smsmith if (buf == Z_NULL) return 0UL; 22575752Smsmith 22675752Smsmith#ifdef DYNAMIC_CRC_TABLE 22775752Smsmith if (crc_table_empty) 22875752Smsmith make_crc_table(); 22975752Smsmith#endif /* DYNAMIC_CRC_TABLE */ 23075752Smsmith 23175752Smsmith#ifdef BYFOUR 23275752Smsmith if (sizeof(void *) == sizeof(ptrdiff_t)) { 23375752Smsmith u4 endian; 234 235 endian = 1; 236 if (*((unsigned char *)(&endian))) 237 return crc32_little(crc, buf, len); 238 else 239 return crc32_big(crc, buf, len); 240 } 241#endif /* BYFOUR */ 242 crc = crc ^ 0xffffffffUL; 243 while (len >= 8) { 244 DO8; 245 len -= 8; 246 } 247 if (len) do { 248 DO1; 249 } while (--len); 250 return crc ^ 0xffffffffUL; 251} 252 253#ifdef BYFOUR 254 255/* ========================================================================= */ 256#define DOLIT4 c ^= *buf4++; \ 257 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ 258 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] 259#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 260 261/* ========================================================================= */ 262local unsigned long crc32_little(crc, buf, len) 263 unsigned long crc; 264 const unsigned char FAR *buf; 265 unsigned len; 266{ 267 register u4 c; 268 register const u4 FAR *buf4; 269 270 c = (u4)crc; 271 c = ~c; 272 while (len && ((ptrdiff_t)buf & 3)) { 273 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 274 len--; 275 } 276 277 buf4 = (const u4 FAR *)(const void FAR *)buf; 278 while (len >= 32) { 279 DOLIT32; 280 len -= 32; 281 } 282 while (len >= 4) { 283 DOLIT4; 284 len -= 4; 285 } 286 buf = (const unsigned char FAR *)buf4; 287 288 if (len) do { 289 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 290 } while (--len); 291 c = ~c; 292 return (unsigned long)c; 293} 294 295/* ========================================================================= */ 296#define DOBIG4 c ^= *++buf4; \ 297 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ 298 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] 299#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 300 301/* ========================================================================= */ 302local unsigned long crc32_big(crc, buf, len) 303 unsigned long crc; 304 const unsigned char FAR *buf; 305 unsigned len; 306{ 307 register u4 c; 308 register const u4 FAR *buf4; 309 310 c = REV((u4)crc); 311 c = ~c; 312 while (len && ((ptrdiff_t)buf & 3)) { 313 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 314 len--; 315 } 316 317 buf4 = (const u4 FAR *)(const void FAR *)buf; 318 buf4--; 319 while (len >= 32) { 320 DOBIG32; 321 len -= 32; 322 } 323 while (len >= 4) { 324 DOBIG4; 325 len -= 4; 326 } 327 buf4++; 328 buf = (const unsigned char FAR *)buf4; 329 330 if (len) do { 331 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 332 } while (--len); 333 c = ~c; 334 return (unsigned long)(REV(c)); 335} 336 337#endif /* BYFOUR */ 338 339#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ 340 341/* ========================================================================= */ 342local unsigned long gf2_matrix_times(mat, vec) 343 unsigned long *mat; 344 unsigned long vec; 345{ 346 unsigned long sum; 347 348 sum = 0; 349 while (vec) { 350 if (vec & 1) 351 sum ^= *mat; 352 vec >>= 1; 353 mat++; 354 } 355 return sum; 356} 357 358/* ========================================================================= */ 359local void gf2_matrix_square(square, mat) 360 unsigned long *square; 361 unsigned long *mat; 362{ 363 int n; 364 365 for (n = 0; n < GF2_DIM; n++) 366 square[n] = gf2_matrix_times(mat, mat[n]); 367} 368 369/* ========================================================================= */ 370uLong ZEXPORT crc32_combine(crc1, crc2, len2) 371 uLong crc1; 372 uLong crc2; 373 z_off_t len2; 374{ 375 int n; 376 unsigned long row; 377 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ 378 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ 379 380 /* degenerate case */ 381 if (len2 == 0) 382 return crc1; 383 384 /* put operator for one zero bit in odd */ 385 odd[0] = 0xedb88320L; /* CRC-32 polynomial */ 386 row = 1; 387 for (n = 1; n < GF2_DIM; n++) { 388 odd[n] = row; 389 row <<= 1; 390 } 391 392 /* put operator for two zero bits in even */ 393 gf2_matrix_square(even, odd); 394 395 /* put operator for four zero bits in odd */ 396 gf2_matrix_square(odd, even); 397 398 /* apply len2 zeros to crc1 (first square will put the operator for one 399 zero byte, eight zero bits, in even) */ 400 do { 401 /* apply zeros operator for this bit of len2 */ 402 gf2_matrix_square(even, odd); 403 if (len2 & 1) 404 crc1 = gf2_matrix_times(even, crc1); 405 len2 >>= 1; 406 407 /* if no more bits set, then done */ 408 if (len2 == 0) 409 break; 410 411 /* another iteration of the loop with odd and even swapped */ 412 gf2_matrix_square(odd, even); 413 if (len2 & 1) 414 crc1 = gf2_matrix_times(odd, crc1); 415 len2 >>= 1; 416 417 /* if no more bits set, then done */ 418 } while (len2 != 0); 419 420 /* return combined crc */ 421 crc1 ^= crc2; 422 return crc1; 423} 424