src/zlib/crc32.c

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