kernel/zmod/crc32.c

   1 /*
   2  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
   3  * Use is subject to license terms.
   4  */
   5
   6 /* crc32.c -- compute the CRC-32 of a data stream
   7  * Copyright (C) 1995-2005 Mark Adler
   8  * For conditions of distribution and use, see copyright notice in zlib.h
   9  *
  10  * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
  11  * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
  12  * tables for updating the shift register in one step with three exclusive-ors
  13  * instead of four steps with four exclusive-ors.  This results in about a
  14  * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
  15  */
  16
  17 /*
  18   Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
  19   protection on the static variables used to control the first-use generation
  20   of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
  21   first call get_crc_table() to initialize the tables before allowing more than
  22   one thread to use crc32().
  23  */
  24
  25 #ifdef MAKECRCH
  26 #  include <stdio.h>
  27 #  ifndef DYNAMIC_CRC_TABLE
  28 #    define DYNAMIC_CRC_TABLE
  29 #  endif /* !DYNAMIC_CRC_TABLE */
  30 #endif /* MAKECRCH */
  31
  32 #include "zutil.h"      /* for STDC and FAR definitions */
  33
  34 #define local static
  35
  36 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
  37 #ifndef NOBYFOUR
  38 #  ifdef STDC           /* need ANSI C limits.h to determine sizes */
  39 #    include <limits.h>
  40 #    define BYFOUR
  41 #    if (UINT_MAX == 0xffffffffUL)
  42        typedef unsigned int u4;
  43 #    else
  44 #      if (ULONG_MAX == 0xffffffffUL)
  45          typedef unsigned long u4;
  46 #      else
  47 #        if (USHRT_MAX == 0xffffffffUL)
  48            typedef unsigned short u4;
  49 #        else
  50 #          undef BYFOUR     /* can't find a four-byte integer type! */
  51 #        endif
  52 #      endif
  53 #    endif
  54 #  endif /* STDC */
  55 #endif /* !NOBYFOUR */
  56
  57 /* Definitions for doing the crc four data bytes at a time. */
  58 #ifdef BYFOUR
  59 #  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
  60                 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
  61    local unsigned long crc32_little OF((unsigned long,
  62                         const unsigned char FAR *, unsigned));
  63    local unsigned long crc32_big OF((unsigned long,
  64                         const unsigned char FAR *, unsigned));
  65 #  define TBLS 8
  66 #else
  67 #  define TBLS 1
  68 #endif /* BYFOUR */
  69
  70 /* Local functions for crc concatenation */
  71 local unsigned long gf2_matrix_times OF((unsigned long *mat,
  72                                          unsigned long vec));
  73 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
  74
  75 #ifdef DYNAMIC_CRC_TABLE
  76
  77 local volatile int crc_table_empty = 1;
  78 local unsigned long FAR crc_table[TBLS][256];
  79 local void make_crc_table OF((void));
  80 #ifdef MAKECRCH
  81    local void write_table OF((FILE *, const unsigned long FAR *));
  82 #endif /* MAKECRCH */
  83 /*
  84   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
  85   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.
  86
  87   Polynomials over GF(2) are represented in binary, one bit per coefficient,
  88   with the lowest powers in the most significant bit.  Then adding polynomials
  89   is just exclusive-or, and multiplying a polynomial by x is a right shift by
  90   one.  If we call the above polynomial p, and represent a byte as the
  91   polynomial q, also with the lowest power in the most significant bit (so the
  92   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
  93   where a mod b means the remainder after dividing a by b.
  94
  95   This calculation is done using the shift-register method of multiplying and
  96   taking the remainder.  The register is initialized to zero, and for each
  97   incoming bit, x^32 is added mod p to the register if the bit is a one (where
  98   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
  99   x (which is shifting right by one and adding x^32 mod p if the bit shifted
 100   out is a one).  We start with the highest power (least significant bit) of
 101   q and repeat for all eight bits of q.
 102
 103   The first table is simply the CRC of all possible eight bit values.  This is
 104   all the information needed to generate CRCs on data a byte at a time for all
 105   combinations of CRC register values and incoming bytes.  The remaining tables
 106   allow for word-at-a-time CRC calculation for both big-endian and little-
 107   endian machines, where a word is four bytes.
 108 */
 109 local void make_crc_table()
 110 {
 111     unsigned long c;
 112     int n, k;
 113     unsigned long poly;                 /* polynomial exclusive-or pattern */
 114     /* terms of polynomial defining this crc (except x^32): */
 115     static volatile int first = 1;      /* flag to limit concurrent making */
 116     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
 117
 118     /* See if another task is already doing this (not thread-safe, but better
 119        than nothing -- significantly reduces duration of vulnerability in
 120        case the advice about DYNAMIC_CRC_TABLE is ignored) */
 121     if (first) {
 122         first = 0;
 123
 124         /* make exclusive-or pattern from polynomial (0xedb88320UL) */
 125         poly = 0UL;
 126         for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
 127             poly |= 1UL << (31 - p[n]);
 128
 129         /* generate a crc for every 8-bit value */
 130         for (n = 0; n < 256; n++) {
 131             c = (unsigned long)n;
 132             for (k = 0; k < 8; k++)
 133                 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
 134             crc_table[0][n] = c;
 135         }
 136
 137 #ifdef BYFOUR
 138         /* generate crc for each value followed by one, two, and three zeros,
 139            and then the byte reversal of those as well as the first table */
 140         for (n = 0; n < 256; n++) {
 141             c = crc_table[0][n];
 142             crc_table[4][n] = REV(c);
 143             for (k = 1; k < 4; k++) {
 144                 c = crc_table[0][c & 0xff] ^ (c >> 8);
 145                 crc_table[k][n] = c;
 146                 crc_table[k + 4][n] = REV(c);
 147             }
 148         }
 149 #endif /* BYFOUR */
 150
 151         crc_table_empty = 0;
 152     }
 153     else {      /* not first */
 154         /* wait for the other guy to finish (not efficient, but rare) */
 155         while (crc_table_empty)
 156             ;
 157     }
 158
 159 #ifdef MAKECRCH
 160     /* write out CRC tables to crc32.h */
 161     {
 162         FILE *out;
 163
 164         out = fopen("crc32.h", "w");
 165         if (out == NULL) return;
 166         fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
 167         fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
 168         fprintf(out, "local const unsigned long FAR ");
 169         fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
 170         write_table(out, crc_table[0]);
 171 #  ifdef BYFOUR
 172         fprintf(out, "#ifdef BYFOUR\n");
 173         for (k = 1; k < 8; k++) {
 174             fprintf(out, "  },\n  {\n");
 175             write_table(out, crc_table[k]);
 176         }
 177         fprintf(out, "#endif\n");
 178 #  endif /* BYFOUR */
 179         fprintf(out, "  }\n};\n");
 180         fclose(out);
 181     }
 182 #endif /* MAKECRCH */
 183 }
 184
 185 #ifdef MAKECRCH
 186 local void write_table(out, table)
 187     FILE *out;
 188     const unsigned long FAR *table;
 189 {
 190     int n;
 191
 192     for (n = 0; n < 256; n++)
 193         fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
 194                 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
 195 }
 196 #endif /* MAKECRCH */
 197
 198 #else /* !DYNAMIC_CRC_TABLE */
 199 /* ========================================================================
 200  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
 201  */
 202 #include "crc32.h"
 203 #endif /* DYNAMIC_CRC_TABLE */
 204
 205 /* =========================================================================
 206  * This function can be used by asm versions of crc32()
 207  */
 208 const unsigned long FAR * ZEXPORT get_crc_table()
 209 {
 210 #ifdef DYNAMIC_CRC_TABLE
 211     if (crc_table_empty)
 212         make_crc_table();
 213 #endif /* DYNAMIC_CRC_TABLE */
 214     return (const unsigned long FAR *)crc_table;
 215 }
 216
 217 /* ========================================================================= */
 218 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
 219 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
 220
 221 /* ========================================================================= */
 222 unsigned long ZEXPORT crc32(crc, buf, len)
 223     unsigned long crc;
 224     const unsigned char FAR *buf;
 225     unsigned len;
 226 {
 227     if (buf == Z_NULL) return 0UL;
 228
 229 #ifdef DYNAMIC_CRC_TABLE
 230     if (crc_table_empty)
 231         make_crc_table();
 232 #endif /* DYNAMIC_CRC_TABLE */
 233
 234 #ifdef BYFOUR
 235     if (sizeof(void *) == sizeof(ptrdiff_t)) {
 236         u4 endian;
 237
 238         endian = 1;
 239         if (*((unsigned char *)(&endian)))
 240             return crc32_little(crc, buf, len);
 241         else
 242             return crc32_big(crc, buf, len);
 243     }
 244 #endif /* BYFOUR */
 245     crc = crc ^ 0xffffffffUL;
 246     while (len >= 8) {
 247         DO8;
 248         len -= 8;
 249     }
 250     if (len) do {
 251         DO1;
 252     } while (--len);
 253     return crc ^ 0xffffffffUL;
 254 }
 255
 256 #ifdef BYFOUR
 257
 258 /* ========================================================================= */
 259 #define DOLIT4 c ^= *buf4++; \
 260         c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
 261             crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
 262 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
 263
 264 /* ========================================================================= */
 265 local unsigned long crc32_little(crc, buf, len)
 266     unsigned long crc;
 267     const unsigned char FAR *buf;
 268     unsigned len;
 269 {
 270     u4 c;
 271     const u4 FAR *buf4;
 272
 273     c = (u4)crc;
 274     c = ~c;
 275     while (len && ((ptrdiff_t)buf & 3)) {
 276         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 277         len--;
 278     }
 279
 280     buf4 = (const u4 FAR *)(const void FAR *)buf;
 281     while (len >= 32) {
 282         DOLIT32;
 283         len -= 32;
 284     }
 285     while (len >= 4) {
 286         DOLIT4;
 287         len -= 4;
 288     }
 289     buf = (const unsigned char FAR *)buf4;
 290
 291     if (len) do {
 292         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 293     } while (--len);
 294     c = ~c;
 295     return (unsigned long)c;
 296 }
 297
 298 /* ========================================================================= */
 299 #define DOBIG4 c ^= *++buf4; \
 300         c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
 301             crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
 302 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
 303
 304 /* ========================================================================= */
 305 local unsigned long crc32_big(crc, buf, len)
 306     unsigned long crc;
 307     const unsigned char FAR *buf;
 308     unsigned len;
 309 {
 310     u4 c;
 311     const u4 FAR *buf4;
 312
 313     c = REV((u4)crc);
 314     c = ~c;
 315     while (len && ((ptrdiff_t)buf & 3)) {
 316         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 317         len--;
 318     }
 319
 320     buf4 = (const u4 FAR *)(const void FAR *)buf;
 321     buf4--;
 322     while (len >= 32) {
 323         DOBIG32;
 324         len -= 32;
 325     }
 326     while (len >= 4) {
 327         DOBIG4;
 328         len -= 4;
 329     }
 330     buf4++;
 331     buf = (const unsigned char FAR *)buf4;
 332
 333     if (len) do {
 334         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 335     } while (--len);
 336     c = ~c;
 337     return (unsigned long)(REV(c));
 338 }
 339
 340 #endif /* BYFOUR */
 341
 342 #define GF2_DIM 32      /* dimension of GF(2) vectors (length of CRC) */
 343
 344 /* ========================================================================= */
 345 local unsigned long gf2_matrix_times(mat, vec)
 346     unsigned long *mat;
 347     unsigned long vec;
 348 {
 349     unsigned long sum;
 350
 351     sum = 0;
 352     while (vec) {
 353         if (vec & 1)
 354             sum ^= *mat;
 355         vec >>= 1;
 356         mat++;
 357     }
 358     return sum;
 359 }
 360
 361 /* ========================================================================= */
 362 local void gf2_matrix_square(square, mat)
 363     unsigned long *square;
 364     unsigned long *mat;
 365 {
 366     int n;
 367
 368     for (n = 0; n < GF2_DIM; n++)
 369         square[n] = gf2_matrix_times(mat, mat[n]);
 370 }
 371
 372 /* ========================================================================= */
 373 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
 374     uLong crc1;
 375     uLong crc2;
 376     z_off_t len2;
 377 {
 378     int n;
 379     unsigned long row;
 380     unsigned long even[GF2_DIM];    /* even-power-of-two zeros operator */
 381     unsigned long odd[GF2_DIM];     /* odd-power-of-two zeros operator */
 382
 383     /* degenerate case */
 384     if (len2 == 0)
 385         return crc1;
 386
 387     /* put operator for one zero bit in odd */
 388     odd[0] = 0xedb88320UL;          /* CRC-32 polynomial */
 389     row = 1;
 390     for (n = 1; n < GF2_DIM; n++) {
 391         odd[n] = row;
 392         row <<= 1;
 393     }
 394
 395     /* put operator for two zero bits in even */
 396     gf2_matrix_square(even, odd);
 397
 398     /* put operator for four zero bits in odd */
 399     gf2_matrix_square(odd, even);
 400
 401     /* apply len2 zeros to crc1 (first square will put the operator for one
 402        zero byte, eight zero bits, in even) */
 403     do {
 404         /* apply zeros operator for this bit of len2 */
 405         gf2_matrix_square(even, odd);
 406         if (len2 & 1)
 407             crc1 = gf2_matrix_times(even, crc1);
 408         len2 >>= 1;
 409
 410         /* if no more bits set, then done */
 411         if (len2 == 0)
 412             break;
 413
 414         /* another iteration of the loop with odd and even swapped */
 415         gf2_matrix_square(odd, even);
 416         if (len2 & 1)
 417             crc1 = gf2_matrix_times(odd, crc1);
 418         len2 >>= 1;
 419
 420         /* if no more bits set, then done */
 421     } while (len2 != 0);
 422
 423     /* return combined crc */
 424     crc1 ^= crc2;
 425     return crc1;
 426 }