crc.cc

   1 /////////////////////////////////////////////////////////////////////////
   2 // $Id: crc.cc,v 1.2 2008/04/07 18:48:11 sshwarts Exp $
   3 /////////////////////////////////////////////////////////////////////////
   4 //
   5 //  I grabbed these CRC routines from the following source:
   6 //    http://www.landfield.com/faqs/compression-faq/part1/section-25.html
   7 //
   8 //  These routines are very useful, so I'm including them in bochs.
   9 //  They are not covered by the license, as they are not my doing.
  10 //  My gratitude to the author for offering them on the 'net.
  11 //
  12 //  I only changed the u_long to Bit32u, and u_char to Bit8u, and gave
  13 //  the functions prototypes.
  14 //
  15 //  -Kevin
  16 //
  17 //  **************************************************************************
  18 //  The following C code (by Rob Warnock <rpw3@sgi.com>) does CRC-32 in
  19 //  BigEndian/BigEndian byte/bit order.  That is, the data is sent most
  20 //  significant byte first, and each of the bits within a byte is sent most
  21 //  significant bit first, as in FDDI. You will need to twiddle with it to do
  22 //  Ethernet CRC, i.e., BigEndian/LittleEndian byte/bit order. [Left as an
  23 //  exercise for the reader.]
  24 //
  25 //  The CRCs this code generates agree with the vendor-supplied Verilog models
  26 //  of several of the popular FDDI "MAC" chips.
  27 //  **************************************************************************
  28
  29 #include "config.h"
  30
  31 /* Initialized first time "crc32()" is called. If you prefer, you can
  32  * statically initialize it at compile time. [Another exercise.]
  33  */
  34 static Bit32u crc32_table[256];
  35
  36 /*
  37  * Build auxiliary table for parallel byte-at-a-time CRC-32.
  38  */
  39 #define CRC32_POLY 0x04c11db7     /* AUTODIN II, Ethernet, & FDDI */
  40
  41 static void init_crc32(void)
  42 {
  43   int i, j;
  44   Bit32u c;
  45
  46   for (i = 0; i < 256; ++i) {
  47     for (c = i << 24, j = 8; j > 0; --j)
  48       c = c & 0x80000000 ? (c << 1) ^ CRC32_POLY : (c << 1);
  49     crc32_table[i] = c;
  50   }
  51 }
  52
  53 Bit32u crc32(const Bit8u *buf, int len)
  54 {
  55   const Bit8u *p;
  56   Bit32u crc;
  57
  58   if (!crc32_table[1])    /* if not already done, */
  59     init_crc32();   /* build table */
  60
  61   crc = 0xffffffff;       /* preload shift register, per CRC-32 spec */
  62   for (p = buf; len > 0; ++p, --len)
  63     crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
  64   return ~crc;            /* transmit complement, per CRC-32 spec */
  65 }