src/zlib/crc32.c

   1 /* crc32.c -- compute the CRC-32 of a data stream
   2  * Copyright (C) 1995-2003 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 about a factor
   9  * of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
  10  */
  11
  12 /* @(#) $Id$ */
  13
  14 #ifdef MAKECRCH
  15 #  include <stdio.h>
  16 #  ifndef DYNAMIC_CRC_TABLE
  17 #    define DYNAMIC_CRC_TABLE
  18 #  endif /* !DYNAMIC_CRC_TABLE */
  19 #endif /* MAKECRCH */
  20
  21 #include "zutil.h"      /* for STDC and FAR definitions */
  22
  23 #define local static
  24
  25 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
  26 #ifndef NOBYFOUR
  27 #  ifdef STDC           /* need ANSI C limits.h to determine sizes */
  28 #    include <limits.h>
  29 #    define BYFOUR
  30 #    if (UINT_MAX == 0xffffffffUL)
  31        typedef unsigned int u4;
  32 #    else
  33 #      if (ULONG_MAX == 0xffffffffUL)
  34          typedef unsigned long u4;
  35 #      else
  36 #        if (USHRT_MAX == 0xffffffffUL)
  37            typedef unsigned short u4;
  38 #        else
  39 #          undef BYFOUR     /* can't find a four-byte integer type! */
  40 #        endif
  41 #      endif
  42 #    endif
  43 #  endif /* STDC */
  44 #endif /* !NOBYFOUR */
  45
  46 /* Definitions for doing the crc four data bytes at a time. */
  47 #ifdef BYFOUR
  48 #  define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
  49                 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
  50    local unsigned long crc32_little OF((unsigned long,
  51                         const unsigned char FAR *, unsigned));
  52    local unsigned long crc32_big OF((unsigned long,
  53                         const unsigned char FAR *, unsigned));
  54 #  define TBLS 8
  55 #else
  56 #  define TBLS 1
  57 #endif /* BYFOUR */
  58
  59 #ifdef DYNAMIC_CRC_TABLE
  60
  61 local int crc_table_empty = 1;
  62 local unsigned long FAR crc_table[TBLS][256];
  63 local void make_crc_table OF((void));
  64 #ifdef MAKECRCH
  65    local void write_table OF((FILE *, const unsigned long FAR *));
  66 #endif /* MAKECRCH */
  67
  68 /*
  69   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
  70   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.
  71
  72   Polynomials over GF(2) are represented in binary, one bit per coefficient,
  73   with the lowest powers in the most significant bit.  Then adding polynomials
  74   is just exclusive-or, and multiplying a polynomial by x is a right shift by
  75   one.  If we call the above polynomial p, and represent a byte as the
  76   polynomial q, also with the lowest power in the most significant bit (so the
  77   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
  78   where a mod b means the remainder after dividing a by b.
  79
  80   This calculation is done using the shift-register method of multiplying and
  81   taking the remainder.  The register is initialized to zero, and for each
  82   incoming bit, x^32 is added mod p to the register if the bit is a one (where
  83   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
  84   x (which is shifting right by one and adding x^32 mod p if the bit shifted
  85   out is a one).  We start with the highest power (least significant bit) of
  86   q and repeat for all eight bits of q.
  87
  88   The first table is simply the CRC of all possible eight bit values.  This is
  89   all the information needed to generate CRCs on data a byte at a time for all
  90   combinations of CRC register values and incoming bytes.  The remaining tables
  91   allow for word-at-a-time CRC calculation for both big-endian and little-
  92   endian machines, where a word is four bytes.
  93 */
  94 local void make_crc_table()
  95 {
  96     unsigned long c;
  97     int n, k;
  98     unsigned long poly;            /* polynomial exclusive-or pattern */
  99     /* terms of polynomial defining this crc (except x^32): */
 100     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
 101
 102     /* make exclusive-or pattern from polynomial (0xedb88320UL) */
 103     poly = 0UL;
 104     for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
 105         poly |= 1UL << (31 - p[n]);
 106
 107     /* generate a crc for every 8-bit value */
 108     for (n = 0; n < 256; n++) {
 109         c = (unsigned long)n;
 110         for (k = 0; k < 8; k++)
 111             c = c & 1 ? poly ^ (c >> 1) : c >> 1;
 112         crc_table[0][n] = c;
 113     }
 114
 115 #ifdef BYFOUR
 116     /* generate crc for each value followed by one, two, and three zeros, and
 117        then the byte reversal of those as well as the first table */
 118     for (n = 0; n < 256; n++) {
 119         c = crc_table[0][n];
 120         crc_table[4][n] = REV(c);
 121         for (k = 1; k < 4; k++) {
 122             c = crc_table[0][c & 0xff] ^ (c >> 8);
 123             crc_table[k][n] = c;
 124             crc_table[k + 4][n] = REV(c);
 125         }
 126     }
 127 #endif /* BYFOUR */
 128
 129   crc_table_empty = 0;
 130
 131 #ifdef MAKECRCH
 132     /* write out CRC tables to crc32.h */
 133     {
 134         FILE *out;
 135
 136         out = fopen("crc32.h", "w");
 137         if (out == NULL) return;
 138         fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
 139         fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
 140         fprintf(out, "local const unsigned long FAR ");
 141         fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
 142         write_table(out, crc_table[0]);
 143 #  ifdef BYFOUR
 144         fprintf(out, "#ifdef BYFOUR\n");
 145         for (k = 1; k < 8; k++) {
 146             fprintf(out, "  },\n  {\n");
 147             write_table(out, crc_table[k]);
 148         }
 149         fprintf(out, "#endif\n");
 150 #  endif /* BYFOUR */
 151         fprintf(out, "  }\n};\n");
 152         fclose(out);
 153     }
 154 #endif /* MAKECRCH */
 155 }
 156
 157 #ifdef MAKECRCH
 158 local void write_table(out, table)
 159     FILE *out;
 160     const unsigned long FAR *table;
 161 {
 162     int n;
 163
 164     for (n = 0; n < 256; n++)
 165         fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
 166                 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
 167 }
 168 #endif /* MAKECRCH */
 169
 170 #else /* !DYNAMIC_CRC_TABLE */
 171 /* ========================================================================
 172  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
 173  */
 174 #include "crc32.h"
 175 #endif /* DYNAMIC_CRC_TABLE */
 176
 177 /* =========================================================================
 178  * This function can be used by asm versions of crc32()
 179  */
 180 const unsigned long FAR * ZEXPORT get_crc_table()
 181 {
 182 #ifdef DYNAMIC_CRC_TABLE
 183   if (crc_table_empty) make_crc_table();
 184 #endif /* DYNAMIC_CRC_TABLE */
 185   return (const unsigned long FAR *)crc_table;
 186 }
 187
 188 /* ========================================================================= */
 189 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
 190 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
 191
 192 /* ========================================================================= */
 193 unsigned long ZEXPORT crc32(crc, buf, len)
 194     unsigned long crc;
 195     const unsigned char FAR *buf;
 196     unsigned len;
 197 {
 198     if (buf == Z_NULL) return 0UL;
 199
 200 #ifdef DYNAMIC_CRC_TABLE
 201     if (crc_table_empty)
 202         make_crc_table();
 203 #endif /* DYNAMIC_CRC_TABLE */
 204
 205 #ifdef BYFOUR
 206     if (sizeof(void *) == sizeof(ptrdiff_t)) {
 207         u4 endian;
 208
 209         endian = 1;
 210         if (*((unsigned char *)(&endian)))
 211             return crc32_little(crc, buf, len);
 212         else
 213             return crc32_big(crc, buf, len);
 214     }
 215 #endif /* BYFOUR */
 216     crc = crc ^ 0xffffffffUL;
 217     while (len >= 8) {
 218         DO8;
 219         len -= 8;
 220     }
 221     if (len) do {
 222         DO1;
 223     } while (--len);
 224     return crc ^ 0xffffffffUL;
 225 }
 226
 227 #ifdef BYFOUR
 228
 229 /* ========================================================================= */
 230 #define DOLIT4 c ^= *buf4++; \
 231         c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
 232             crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
 233 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
 234
 235 /* ========================================================================= */
 236 local unsigned long crc32_little(crc, buf, len)
 237     unsigned long crc;
 238     const unsigned char FAR *buf;
 239     unsigned len;
 240 {
 241     register u4 c;
 242     register const u4 FAR *buf4;
 243
 244     c = (u4)crc;
 245     c = ~c;
 246     while (len && ((ptrdiff_t)buf & 3)) {
 247         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 248         len--;
 249     }
 250
 251     buf4 = (const u4 FAR *)buf;
 252     while (len >= 32) {
 253         DOLIT32;
 254         len -= 32;
 255     }
 256     while (len >= 4) {
 257         DOLIT4;
 258         len -= 4;
 259     }
 260     buf = (const unsigned char FAR *)buf4;
 261
 262     if (len) do {
 263         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
 264     } while (--len);
 265     c = ~c;
 266     return (unsigned long)c;
 267 }
 268
 269 /* ========================================================================= */
 270 #define DOBIG4 c ^= *++buf4; \
 271         c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
 272             crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
 273 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
 274
 275 /* ========================================================================= */
 276 local unsigned long crc32_big(crc, buf, len)
 277     unsigned long crc;
 278     const unsigned char FAR *buf;
 279     unsigned len;
 280 {
 281     register u4 c;
 282     register const u4 FAR *buf4;
 283
 284     c = REV((u4)crc);
 285     c = ~c;
 286     while (len && ((ptrdiff_t)buf & 3)) {
 287         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 288         len--;
 289     }
 290
 291     buf4 = (const u4 FAR *)buf;
 292     buf4--;
 293     while (len >= 32) {
 294         DOBIG32;
 295         len -= 32;
 296     }
 297     while (len >= 4) {
 298         DOBIG4;
 299         len -= 4;
 300     }
 301     buf4++;
 302     buf = (const unsigned char FAR *)buf4;
 303
 304     if (len) do {
 305         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
 306     } while (--len);
 307     c = ~c;
 308     return (unsigned long)(REV(c));
 309 }
 310
 311 #endif /* BYFOUR */