libkern/zlib/crc32.c

   1 /*
   2  * Copyright (c) 2008 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28 /* crc32.c -- compute the CRC-32 of a data stream
  29  * Copyright (C) 1995-2005 Mark Adler
  30  * For conditions of distribution and use, see copyright notice in zlib.h
  31  *
  32  * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
  33  * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
  34  * tables for updating the shift register in one step with three exclusive-ors
  35  * instead of four steps with four exclusive-ors.  This results in about a
  36  * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
  37  */
  38
  39 /* @(#) $Id$ */
  40
  41 /*
  42   Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
  43   protection on the static variables used to control the first-use generation
  44   of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
  45   first call get_crc_table() to initialize the tables before allowing more than
  46   one thread to use crc32().
  47  */
  48
  49
  50 #ifdef MAKECRCH
  51 #  include <stdio.h>
  52 #  ifndef DYNAMIC_CRC_TABLE
  53 #    define DYNAMIC_CRC_TABLE
  54 #  endif /* !DYNAMIC_CRC_TABLE */
  55 #endif /* MAKECRCH */
  56
  57 #include "zutil.h"      /* for STDC and FAR definitions */
  58
  59 #define local static
  60
  61 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
  62 #ifndef NOBYFOUR
  63 #  ifdef STDC           /* need ANSI C limits.h to determine sizes */
  64 #    include <machine/limits.h>
  65 #    define BYFOUR
  66 #    if (UINT_MAX == 0xffffffffUL)
  67        typedef unsigned int u4;
  68 #    else
  69 #      if (ULONG_MAX == 0xffffffffUL)
  70          typedef unsigned long u4;
  71 #      else
  72 #        if (USHRT_MAX == 0xffffffffUL)
  73            typedef unsigned short u4;
  74 #        else
  75 #          undef BYFOUR     /* can't find a four-byte integer type! */
  76 #        endif
  77 #      endif
  78 #    endif
  79 #  endif /* STDC */
  80 #endif /* !NOBYFOUR */
  81
  82 /* Definitions for doing the crc four data bytes at a time. */
  83 #ifdef BYFOUR
  84 #  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
  85                 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
  86    local unsigned long crc32_little OF((unsigned long,
  87                         const unsigned char FAR *, unsigned));
  88    local unsigned long crc32_big OF((unsigned long,
  89                         const unsigned char FAR *, unsigned));
  90 #  define TBLS 8
  91 #else
  92 #  define TBLS 1
  93 #endif /* BYFOUR */
  94
  95 /* Local functions for crc concatenation */
  96 local unsigned long gf2_matrix_times OF((unsigned long *mat,
  97                                          unsigned long vec));
  98 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
  99
 100 #ifdef DYNAMIC_CRC_TABLE
 101
 102 local volatile int crc_table_empty = 1;
 103 local unsigned long FAR crc_table[TBLS][256];
 104 local void make_crc_table OF((void));
 105 #ifdef MAKECRCH
 106    local void write_table OF((FILE *, const unsigned long FAR *));
 107 #endif /* MAKECRCH */
 108 /*
 109   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
 110   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.
 111
 112   Polynomials over GF(2) are represented in binary, one bit per coefficient,
 113   with the lowest powers in the most significant bit.  Then adding polynomials
 114   is just exclusive-or, and multiplying a polynomial by x is a right shift by
 115   one.  If we call the above polynomial p, and represent a byte as the
 116   polynomial q, also with the lowest power in the most significant bit (so the
 117   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
 118   where a mod b means the remainder after dividing a by b.
 119
 120   This calculation is done using the shift-register method of multiplying and
 121   taking the remainder.  The register is initialized to zero, and for each
 122   incoming bit, x^32 is added mod p to the register if the bit is a one (where
 123   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
 124   x (which is shifting right by one and adding x^32 mod p if the bit shifted
 125   out is a one).  We start with the highest power (least significant bit) of
 126   q and repeat for all eight bits of q.
 127
 128   The first table is simply the CRC of all possible eight bit values.  This is
 129   all the information needed to generate CRCs on data a byte at a time for all
 130   combinations of CRC register values and incoming bytes.  The remaining tables
 131   allow for word-at-a-time CRC calculation for both big-endian and little-
 132   endian machines, where a word is four bytes.
 133 */
 134 local void make_crc_table()
 135 {
 136     unsigned long c;
 137     int n, k;
 138     unsigned long poly;                 /* polynomial exclusive-or pattern */
 139     /* terms of polynomial defining this crc (except x^32): */
 140     static volatile int first = 1;      /* flag to limit concurrent making */
 141     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
 142
 143     /* See if another task is already doing this (not thread-safe, but better
 144        than nothing -- significantly reduces duration of vulnerability in
 145        case the advice about DYNAMIC_CRC_TABLE is ignored) */
 146     if (first) {
 147         first = 0;
 148
 149         /* make exclusive-or pattern from polynomial (0xedb88320UL) */
 150         poly = 0UL;
 151         for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
 152             poly |= 1UL << (31 - p[n]);
 153
 154         /* generate a crc for every 8-bit value */
 155         for (n = 0; n < 256; n++) {
 156             c = (unsigned long)n;
 157             for (k = 0; k < 8; k++)
 158                 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
 159             crc_table[0][n] = c;
 160         }
 161
 162 #ifdef BYFOUR
 163         /* generate crc for each value followed by one, two, and three zeros,
 164            and then the byte reversal of those as well as the first table */
 165         for (n = 0; n < 256; n++) {
 166             c = crc_table[0][n];
 167             crc_table[4][n] = REV(c);
 168             for (k = 1; k < 4; k++) {
 169                 c = crc_table[0][c & 0xff] ^ (c >> 8);
 170                 crc_table[k][n] = c;
 171                 crc_table[k + 4][n] = REV(c);
 172             }
 173         }
 174 #endif /* BYFOUR */
 175
 176         crc_table_empty = 0;
 177     }
 178     else {      /* not first */
 179         /* wait for the other guy to finish (not efficient, but rare) */
 180         while (crc_table_empty)
 181             ;
 182     }
 183
 184 #ifdef MAKECRCH
 185     /* write out CRC tables to crc32.h */
 186     {
 187         FILE *out;
 188
 189         out = fopen("crc32.h", "w");
 190         if (out == NULL) return;
 191         fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
 192         fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
 193         fprintf(out, "local const unsigned long FAR ");
 194         fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
 195         write_table(out, crc_table[0]);
 196 #  ifdef BYFOUR
 197         fprintf(out, "#ifdef BYFOUR\n");
 198         for (k = 1; k < 8; k++) {
 199             fprintf(out, "  },\n  {\n");
 200             write_table(out, crc_table[k]);
 201         }
 202         fprintf(out, "#endif\n");
 203 #  endif /* BYFOUR */
 204         fprintf(out, "  }\n};\n");
 205         fclose(out);
 206     }
 207 #endif /* MAKECRCH */
 208 }
 209
 210 #ifdef MAKECRCH
 211 local void write_table(out, table)
 212     FILE *out;
 213     const unsigned long FAR *table;
 214 {
 215     int n;
 216
 217     for (n = 0; n < 256; n++)
 218         fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
 219                 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
 220 }
 221 #endif /* MAKECRCH */
 222
 223 #else /* !DYNAMIC_CRC_TABLE */
 224 /* ========================================================================
 225  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
 226  */
 227 #include "crc32.h"
 228 #endif /* DYNAMIC_CRC_TABLE */
 229
 230 /* =========================================================================
 231  * This function can be used by asm versions of crc32()
 232  */
 233 const unsigned long FAR * ZEXPORT get_crc_table()
 234 {
 235 #ifdef DYNAMIC_CRC_TABLE
 236     if (crc_table_empty)
 237         make_crc_table();
 238 #endif /* DYNAMIC_CRC_TABLE */
 239     return (const unsigned long FAR *)crc_table;
 240 }
 241
 242 /* ========================================================================= */
 243 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
 244 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
 245
 246 /* ========================================================================= */
 247 unsigned long ZEXPORT z_crc32(crc, buf, len)
 248     unsigned long crc;
 249     const unsigned char FAR *buf;
 250     unsigned len;
 251 {
 252     if (buf == Z_NULL) return 0UL;
 253
 254 #ifdef DYNAMIC_CRC_TABLE
 255     if (crc_table_empty)
 256         make_crc_table();
 257 #endif /* DYNAMIC_CRC_TABLE */
 258
 259 #ifdef BYFOUR
 260     if (sizeof(void *) == sizeof(ptrdiff_t)) {
 261         u4 endian;
 262
 263         endian = 1;
 264         if (*((unsigned char *)(&endian)))
 265             return crc32_little(crc, buf, len);
 266         else
 267             return crc32_big(crc, buf, len);
 268     }
 269 #endif /* BYFOUR */
 270     crc = crc ^ 0xffffffffUL;
 271     while (len >= 8) {
 272         DO8;
 273         len -= 8;
 274     }
 275     if (len) do {
 276         DO1;
 277     } while (--len);
 278     return crc ^ 0xffffffffUL;
 279 }
 280
 281 #ifdef BYFOUR
 282
 283 /* ========================================================================= */
 284 #define DOLIT4 c ^= *buf4++; \
 285         c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
 286             crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
 287 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
 288
 289 /* ========================================================================= */
 290 local unsigned long crc32_little(crc, buf, len)
 291     unsigned long crc;
 292     const unsigned char FAR *buf;
 293     unsigned len;
 294 {
 295     register u4 c;
 296     register const u4 FAR *buf4;
 297
 298     c = (u4)crc;
 299     c = ~c;
 300     while (len && ((ptrdiff_t)buf & 3)) {
 301         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 302         len--;
 303     }
 304
 305     buf4 = (const u4 FAR *)(const void FAR *)buf;
 306     while (len >= 32) {
 307         DOLIT32;
 308         len -= 32;
 309     }
 310     while (len >= 4) {
 311         DOLIT4;
 312         len -= 4;
 313     }
 314     buf = (const unsigned char FAR *)buf4;
 315
 316     if (len) do {
 317         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 318     } while (--len);
 319     c = ~c;
 320     return (unsigned long)c;
 321 }
 322
 323 /* ========================================================================= */
 324 #define DOBIG4 c ^= *++buf4; \
 325         c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
 326             crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
 327 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
 328
 329 /* ========================================================================= */
 330 local unsigned long crc32_big(crc, buf, len)
 331     unsigned long crc;
 332     const unsigned char FAR *buf;
 333     unsigned len;
 334 {
 335     register u4 c;
 336     register const u4 FAR *buf4;
 337
 338     c = REV((u4)crc);
 339     c = ~c;
 340     while (len && ((ptrdiff_t)buf & 3)) {
 341         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 342         len--;
 343     }
 344
 345     buf4 = (const u4 FAR *)(const void FAR *)buf;
 346     buf4--;
 347     while (len >= 32) {
 348         DOBIG32;
 349         len -= 32;
 350     }
 351     while (len >= 4) {
 352         DOBIG4;
 353         len -= 4;
 354     }
 355     buf4++;
 356     buf = (const unsigned char FAR *)buf4;
 357
 358     if (len) do {
 359         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 360     } while (--len);
 361     c = ~c;
 362     return (unsigned long)(REV(c));
 363 }
 364
 365 #endif /* BYFOUR */
 366
 367 #define GF2_DIM 32      /* dimension of GF(2) vectors (length of CRC) */
 368
 369 /* ========================================================================= */
 370 local unsigned long gf2_matrix_times(mat, vec)
 371     unsigned long *mat;
 372     unsigned long vec;
 373 {
 374     unsigned long sum;
 375
 376     sum = 0;
 377     while (vec) {
 378         if (vec & 1)
 379             sum ^= *mat;
 380         vec >>= 1;
 381         mat++;
 382     }
 383     return sum;
 384 }
 385
 386 /* ========================================================================= */
 387 local void gf2_matrix_square(square, mat)
 388     unsigned long *square;
 389     unsigned long *mat;
 390 {
 391     int n;
 392
 393     for (n = 0; n < GF2_DIM; n++)
 394         square[n] = gf2_matrix_times(mat, mat[n]);
 395 }
 396
 397 /* ========================================================================= */
 398 uLong ZEXPORT z_crc32_combine(crc1, crc2, len2)
 399     uLong crc1;
 400     uLong crc2;
 401     z_off_t len2;
 402 {
 403     int n;
 404     unsigned long row;
 405     unsigned long even[GF2_DIM];    /* even-power-of-two zeros operator */
 406     unsigned long odd[GF2_DIM];     /* odd-power-of-two zeros operator */
 407
 408     /* degenerate case */
 409     if (len2 == 0)
 410         return crc1;
 411
 412     /* put operator for one zero bit in odd */
 413     odd[0] = 0xedb88320L;           /* CRC-32 polynomial */
 414     row = 1;
 415     for (n = 1; n < GF2_DIM; n++) {
 416         odd[n] = row;
 417         row <<= 1;
 418     }
 419
 420     /* put operator for two zero bits in even */
 421     gf2_matrix_square(even, odd);
 422
 423     /* put operator for four zero bits in odd */
 424     gf2_matrix_square(odd, even);
 425
 426     /* apply len2 zeros to crc1 (first square will put the operator for one
 427        zero byte, eight zero bits, in even) */
 428     do {
 429         /* apply zeros operator for this bit of len2 */
 430         gf2_matrix_square(even, odd);
 431         if (len2 & 1)
 432             crc1 = gf2_matrix_times(even, crc1);
 433         len2 >>= 1;
 434
 435         /* if no more bits set, then done */
 436         if (len2 == 0)
 437             break;
 438
 439         /* another iteration of the loop with odd and even swapped */
 440         gf2_matrix_square(odd, even);
 441         if (len2 & 1)
 442             crc1 = gf2_matrix_times(odd, crc1);
 443         len2 >>= 1;
 444
 445         /* if no more bits set, then done */
 446     } while (len2 != 0);
 447
 448     /* return combined crc */
 449     crc1 ^= crc2;
 450     return crc1;
 451 }