zlib/crc32.c

   1 /* crc32.c -- compute the CRC-32 of a data stream
   2  * Copyright (C) 1995-2006, 2010, 2011, 2012, 2016 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 /* @(#) $Id: crc32.c,v 1.1.1.2 2002/03/11 21:53:23 tromey Exp $ */
  13
  14 /*
  15   Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
  16   protection on the static variables used to control the first-use generation
  17   of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
  18   first call get_crc_table() to initialize the tables before allowing more than
  19   one thread to use crc32().
  20
  21   DYNAMIC_CRC_TABLE and MAKECRCH can be #defined to write out crc32.h.
  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 /* Definitions for doing the crc four data bytes at a time. */
  34 #if !defined(NOBYFOUR) && defined(Z_U4)
  35 #  define BYFOUR
  36 #endif
  37 #ifdef BYFOUR
  38    local unsigned long crc32_little OF((unsigned long,
  39                         const unsigned char FAR *, z_size_t));
  40    local unsigned long crc32_big OF((unsigned long,
  41                         const unsigned char FAR *, z_size_t));
  42 #  define TBLS 8
  43 #else
  44 #  define TBLS 1
  45 #endif /* BYFOUR */
  46
  47 /* Local functions for crc concatenation */
  48 local unsigned long gf2_matrix_times OF((unsigned long *mat,
  49                                          unsigned long vec));
  50 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
  51 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
  52
  53
  54 #ifdef DYNAMIC_CRC_TABLE
  55
  56 local volatile int crc_table_empty = 1;
  57 local z_crc_t FAR crc_table[TBLS][256];
  58 local void make_crc_table OF((void));
  59 #ifdef MAKECRCH
  60    local void write_table OF((FILE *, const z_crc_t FAR *));
  61 #endif /* MAKECRCH */
  62 /*
  63   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
  64   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.
  65
  66   Polynomials over GF(2) are represented in binary, one bit per coefficient,
  67   with the lowest powers in the most significant bit.  Then adding polynomials
  68   is just exclusive-or, and multiplying a polynomial by x is a right shift by
  69   one.  If we call the above polynomial p, and represent a byte as the
  70   polynomial q, also with the lowest power in the most significant bit (so the
  71   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
  72   where a mod b means the remainder after dividing a by b.
  73
  74   This calculation is done using the shift-register method of multiplying and
  75   taking the remainder.  The register is initialized to zero, and for each
  76   incoming bit, x^32 is added mod p to the register if the bit is a one (where
  77   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
  78   x (which is shifting right by one and adding x^32 mod p if the bit shifted
  79   out is a one).  We start with the highest power (least significant bit) of
  80   q and repeat for all eight bits of q.
  81
  82   The first table is simply the CRC of all possible eight bit values.  This is
  83   all the information needed to generate CRCs on data a byte at a time for all
  84   combinations of CRC register values and incoming bytes.  The remaining tables
  85   allow for word-at-a-time CRC calculation for both big-endian and little-
  86   endian machines, where a word is four bytes.
  87 */
  88 local void make_crc_table()
  89 {
  90     z_crc_t c;
  91     int n, k;
  92     z_crc_t poly;                       /* polynomial exclusive-or pattern */
  93     /* terms of polynomial defining this crc (except x^32): */
  94     static volatile int first = 1;      /* flag to limit concurrent making */
  95     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
  96
  97     /* See if another task is already doing this (not thread-safe, but better
  98        than nothing -- significantly reduces duration of vulnerability in
  99        case the advice about DYNAMIC_CRC_TABLE is ignored) */
 100     if (first) {
 101         first = 0;
 102
 103         /* make exclusive-or pattern from polynomial (0xedb88320UL) */
 104         poly = 0;
 105         for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
 106             poly |= (z_crc_t)1 << (31 - p[n]);
 107
 108         /* generate a crc for every 8-bit value */
 109         for (n = 0; n < 256; n++) {
 110             c = (z_crc_t)n;
 111             for (k = 0; k < 8; k++)
 112                 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
 113             crc_table[0][n] = c;
 114         }
 115
 116 #ifdef BYFOUR
 117         /* generate crc for each value followed by one, two, and three zeros,
 118            and then the byte reversal of those as well as the first table */
 119         for (n = 0; n < 256; n++) {
 120             c = crc_table[0][n];
 121             crc_table[4][n] = ZSWAP32(c);
 122             for (k = 1; k < 4; k++) {
 123                 c = crc_table[0][c & 0xff] ^ (c >> 8);
 124                 crc_table[k][n] = c;
 125                 crc_table[k + 4][n] = ZSWAP32(c);
 126             }
 127         }
 128 #endif /* BYFOUR */
 129
 130         crc_table_empty = 0;
 131     }
 132     else {      /* not first */
 133         /* wait for the other guy to finish (not efficient, but rare) */
 134         while (crc_table_empty)
 135             ;
 136     }
 137
 138 #ifdef MAKECRCH
 139     /* write out CRC tables to crc32.h */
 140     {
 141         FILE *out;
 142
 143         out = fopen("crc32.h", "w");
 144         if (out == NULL) return;
 145         fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
 146         fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
 147         fprintf(out, "local const z_crc_t FAR ");
 148         fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
 149         write_table(out, crc_table[0]);
 150 #  ifdef BYFOUR
 151         fprintf(out, "#ifdef BYFOUR\n");
 152         for (k = 1; k < 8; k++) {
 153             fprintf(out, "  },\n  {\n");
 154             write_table(out, crc_table[k]);
 155         }
 156         fprintf(out, "#endif\n");
 157 #  endif /* BYFOUR */
 158         fprintf(out, "  }\n};\n");
 159         fclose(out);
 160     }
 161 #endif /* MAKECRCH */
 162 }
 163
 164 #ifdef MAKECRCH
 165 local void write_table(out, table)
 166     FILE *out;
 167     const z_crc_t FAR *table;
 168 {
 169     int n;
 170
 171     for (n = 0; n < 256; n++)
 172         fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ",
 173                 (unsigned long)(table[n]),
 174                 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
 175 }
 176 #endif /* MAKECRCH */
 177
 178 #else /* !DYNAMIC_CRC_TABLE */
 179 /* ========================================================================
 180  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
 181  */
 182 #include "crc32.h"
 183 #endif /* DYNAMIC_CRC_TABLE */
 184
 185 /* =========================================================================
 186  * This function can be used by asm versions of crc32()
 187  */
 188 const z_crc_t FAR * ZEXPORT get_crc_table()
 189 {
 190 #ifdef DYNAMIC_CRC_TABLE
 191     if (crc_table_empty)
 192         make_crc_table();
 193 #endif /* DYNAMIC_CRC_TABLE */
 194     return (const z_crc_t FAR *)crc_table;
 195 }
 196
 197 /* ========================================================================= */
 198 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
 199 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
 200
 201 /* ========================================================================= */
 202 unsigned long ZEXPORT crc32_z(crc, buf, len)
 203     unsigned long crc;
 204     const unsigned char FAR *buf;
 205     z_size_t len;
 206 {
 207     if (buf == Z_NULL) return 0UL;
 208
 209 #ifdef DYNAMIC_CRC_TABLE
 210     if (crc_table_empty)
 211         make_crc_table();
 212 #endif /* DYNAMIC_CRC_TABLE */
 213
 214 #ifdef BYFOUR
 215     if (sizeof(void *) == sizeof(ptrdiff_t)) {
 216         z_crc_t endian;
 217
 218         endian = 1;
 219         if (*((unsigned char *)(&endian)))
 220             return crc32_little(crc, buf, len);
 221         else
 222             return crc32_big(crc, buf, len);
 223     }
 224 #endif /* BYFOUR */
 225     crc = crc ^ 0xffffffffUL;
 226     while (len >= 8) {
 227         DO8;
 228         len -= 8;
 229     }
 230     if (len) do {
 231         DO1;
 232     } while (--len);
 233     return crc ^ 0xffffffffUL;
 234 }
 235
 236 /* ========================================================================= */
 237 unsigned long ZEXPORT crc32(crc, buf, len)
 238     unsigned long crc;
 239     const unsigned char FAR *buf;
 240     uInt len;
 241 {
 242     return crc32_z(crc, buf, len);
 243 }
 244
 245 #ifdef BYFOUR
 246
 247 /*
 248    This BYFOUR code accesses the passed unsigned char * buffer with a 32-bit
 249    integer pointer type. This violates the strict aliasing rule, where a
 250    compiler can assume, for optimization purposes, that two pointers to
 251    fundamentally different types won't ever point to the same memory. This can
 252    manifest as a problem only if one of the pointers is written to. This code
 253    only reads from those pointers. So long as this code remains isolated in
 254    this compilation unit, there won't be a problem. For this reason, this code
 255    should not be copied and pasted into a compilation unit in which other code
 256    writes to the buffer that is passed to these routines.
 257  */
 258
 259 /* ========================================================================= */
 260 #define DOLIT4 c ^= *buf4++; \
 261         c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
 262             crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
 263 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
 264
 265 /* ========================================================================= */
 266 local unsigned long crc32_little(crc, buf, len)
 267     unsigned long crc;
 268     const unsigned char FAR *buf;
 269     z_size_t len;
 270 {
 271     register z_crc_t c;
 272     register const z_crc_t FAR *buf4;
 273
 274     c = (z_crc_t)crc;
 275     c = ~c;
 276     while (len && ((ptrdiff_t)buf & 3)) {
 277         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 278         len--;
 279     }
 280
 281     buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
 282     while (len >= 32) {
 283         DOLIT32;
 284         len -= 32;
 285     }
 286     while (len >= 4) {
 287         DOLIT4;
 288         len -= 4;
 289     }
 290     buf = (const unsigned char FAR *)buf4;
 291
 292     if (len) do {
 293         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 294     } while (--len);
 295     c = ~c;
 296     return (unsigned long)c;
 297 }
 298
 299 /* ========================================================================= */
 300 #define DOBIG4 c ^= *buf4++; \
 301         c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
 302             crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
 303 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
 304
 305 /* ========================================================================= */
 306 local unsigned long crc32_big(crc, buf, len)
 307     unsigned long crc;
 308     const unsigned char FAR *buf;
 309     z_size_t len;
 310 {
 311     register z_crc_t c;
 312     register const z_crc_t FAR *buf4;
 313
 314     c = ZSWAP32((z_crc_t)crc);
 315     c = ~c;
 316     while (len && ((ptrdiff_t)buf & 3)) {
 317         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 318         len--;
 319     }
 320
 321     buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
 322     while (len >= 32) {
 323         DOBIG32;
 324         len -= 32;
 325     }
 326     while (len >= 4) {
 327         DOBIG4;
 328         len -= 4;
 329     }
 330     buf = (const unsigned char FAR *)buf4;
 331
 332     if (len) do {
 333         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 334     } while (--len);
 335     c = ~c;
 336     return (unsigned long)(ZSWAP32(c));
 337 }
 338
 339 #endif /* BYFOUR */
 340
 341 #define GF2_DIM 32      /* dimension of GF(2) vectors (length of CRC) */
 342
 343 /* ========================================================================= */
 344 local unsigned long gf2_matrix_times(mat, vec)
 345     unsigned long *mat;
 346     unsigned long vec;
 347 {
 348     unsigned long sum;
 349
 350     sum = 0;
 351     while (vec) {
 352         if (vec & 1)
 353             sum ^= *mat;
 354         vec >>= 1;
 355         mat++;
 356     }
 357     return sum;
 358 }
 359
 360 /* ========================================================================= */
 361 local void gf2_matrix_square(square, mat)
 362     unsigned long *square;
 363     unsigned long *mat;
 364 {
 365     int n;
 366
 367     for (n = 0; n < GF2_DIM; n++)
 368         square[n] = gf2_matrix_times(mat, mat[n]);
 369 }
 370
 371 /* ========================================================================= */
 372 local uLong crc32_combine_(crc1, crc2, len2)
 373     uLong crc1;
 374     uLong crc2;
 375     z_off64_t len2;
 376 {
 377     int n;
 378     unsigned long row;
 379     unsigned long even[GF2_DIM];    /* even-power-of-two zeros operator */
 380     unsigned long odd[GF2_DIM];     /* odd-power-of-two zeros operator */
 381
 382     /* degenerate case (also disallow negative lengths) */
 383     if (len2 <= 0)
 384         return crc1;
 385
 386     /* put operator for one zero bit in odd */
 387     odd[0] = 0xedb88320UL;          /* CRC-32 polynomial */
 388     row = 1;
 389     for (n = 1; n < GF2_DIM; n++) {
 390         odd[n] = row;
 391         row <<= 1;
 392     }
 393
 394     /* put operator for two zero bits in even */
 395     gf2_matrix_square(even, odd);
 396
 397     /* put operator for four zero bits in odd */
 398     gf2_matrix_square(odd, even);
 399
 400     /* apply len2 zeros to crc1 (first square will put the operator for one
 401        zero byte, eight zero bits, in even) */
 402     do {
 403         /* apply zeros operator for this bit of len2 */
 404         gf2_matrix_square(even, odd);
 405         if (len2 & 1)
 406             crc1 = gf2_matrix_times(even, crc1);
 407         len2 >>= 1;
 408
 409         /* if no more bits set, then done */
 410         if (len2 == 0)
 411             break;
 412
 413         /* another iteration of the loop with odd and even swapped */
 414         gf2_matrix_square(odd, even);
 415         if (len2 & 1)
 416             crc1 = gf2_matrix_times(odd, crc1);
 417         len2 >>= 1;
 418
 419         /* if no more bits set, then done */
 420     } while (len2 != 0);
 421
 422     /* return combined crc */
 423     crc1 ^= crc2;
 424     return crc1;
 425 }
 426
 427 /* ========================================================================= */
 428 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
 429     uLong crc1;
 430     uLong crc2;
 431     z_off_t len2;
 432 {
 433     return crc32_combine_(crc1, crc2, len2);
 434 }
 435
 436 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
 437     uLong crc1;
 438     uLong crc2;
 439     z_off64_t len2;
 440 {
 441     return crc32_combine_(crc1, crc2, len2);
 442 }