unit crc32;
{
  /* ============================================================= */
  /*  COPYRIGHT (C) 1986 Gary S. Brown.  You may use this program, or   
    */
  /*  code or tables extracted from it, as desired without restriction. 
    */
  /*                                                                    
    */
  /*  First, the polynomial itself and its table of feedback terms.  The 
   */
  /*  polynomial is                                                     
    */
  /*  
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+X^0   */
  /*                                                                    
    */
  /*  Note that we take it "backwards" and put the highest-order term in 
   */
  /*  the lowest-order bit.  The X^32 term is "implied"; the LSB is the 
    */
  /*  X^31 term, etc.  The X^0 term (usually shown as "+1") results in  
    */
  /*  the MSB being 1.                                                  
    */
  /*                                                                    
    */
  /*  Note that the usual hardware shift register implementation, which 
    */
  /*  is what we're using (we're merely optimizing it by doing eight-bit 
   */
  /*  chunks at a time) shifts bits into the lowest-order term.  In our 
    */
  /*  implementation, that means shifting towards the right.  Why do we 
    */
  /*  do it this way?  Because the calculated CRC must be transmitted in 
   */
  /*  order from highest-order term to lowest-order term.  UARTs 
transmit   */
  /*  characters in order from LSB to MSB.  By storing the CRC this way, 
   */
  /*  we hand it to the UART in the order low-byte to high-byte; the 
UART   */
  /*  sends each low-bit to hight-bit; and the result is transmission 
bit   */
  /*  by bit from highest- to lowest-order term without requiring any 
bit   */
  /*  shuffling on our part.  Reception works similarly.                
    */
  /*                                                                    
    */
  /*  The feedback terms table consists of 256, 32-bit entries.  Notes: 
    */
  /*                                                                    
    */
  /*      The table can be generated at runtime if desired; code to do 
so   */
  /*      is shown later.  It might not be obvious, but the feedback    
    */
  /*      terms simply represent the results of eight shift/xor opera-  
    */
  /*      tions for all combinations of data and CRC register values.   
    */
  /*                                                                    
    */
  /*      The values must be right-shifted by eight bits by the "updcrc" 
   */
  /*      logic; the shift must be unsigned (bring in zeroes).  On some 
    */
  /*      hardware you could probably optimize the shift in assembler by 
   */
  /*      using byte-swap instructions.                                 
    */
  /*      polynomial $edb88320                                          
    */
  /*                                                                    
    */
  /*  
--------------------------------------------------------------------  */
}

interface

type
  pbyte = ^byte;
  longrec = record
    lo,hi : word;
  end;

var
  crc32val : longint;


procedure updatecrc(s : pchar; len : integer);

implementation

const
  crc_32_tab : array[0..255] of longint = (
      $00000000, $77073096, $ee0e612c, $990951ba, $076dc419,
      $706af48f, $e963a535, $9e6495a3, $0edb8832, $79dcb8a4,
      $e0d5e91e, $97d2d988, $09b64c2b, $7eb17cbd, $e7b82d07,
      $90bf1d91, $1db71064, $6ab020f2, $f3b97148, $84be41de,
      $1adad47d, $6ddde4eb, $f4d4b551, $83d385c7, $136c9856,
      $646ba8c0, $fd62f97a, $8a65c9ec, $14015c4f, $63066cd9,
      $fa0f3d63, $8d080df5, $3b6e20c8, $4c69105e, $d56041e4,
      $a2677172, $3c03e4d1, $4b04d447, $d20d85fd, $a50ab56b,
      $35b5a8fa, $42b2986c, $dbbbc9d6, $acbcf940, $32d86ce3,
      $45df5c75, $dcd60dcf, $abd13d59, $26d930ac, $51de003a,
      $c8d75180, $bfd06116, $21b4f4b5, $56b3c423, $cfba9599,
      $b8bda50f, $2802b89e, $5f058808, $c60cd9b2, $b10be924,
      $2f6f7c87, $58684c11, $c1611dab, $b6662d3d, $76dc4190,
      $01db7106, $98d220bc, $efd5102a, $71b18589, $06b6b51f,
      $9fbfe4a5, $e8b8d433, $7807c9a2, $0f00f934, $9609a88e,
      $e10e9818, $7f6a0dbb, $086d3d2d, $91646c97, $e6635c01,
      $6b6b51f4, $1c6c6162, $856530d8, $f262004e, $6c0695ed,
      $1b01a57b, $8208f4c1, $f50fc457, $65b0d9c6, $12b7e950,
      $8bbeb8ea, $fcb9887c, $62dd1ddf, $15da2d49, $8cd37cf3,
      $fbd44c65, $4db26158, $3ab551ce, $a3bc0074, $d4bb30e2,
      $4adfa541, $3dd895d7, $a4d1c46d, $d3d6f4fb, $4369e96a,
      $346ed9fc, $ad678846, $da60b8d0, $44042d73, $33031de5,
      $aa0a4c5f, $dd0d7cc9, $5005713c, $270241aa, $be0b1010,
      $c90c2086, $5768b525, $206f85b3, $b966d409, $ce61e49f,
      $5edef90e, $29d9c998, $b0d09822, $c7d7a8b4, $59b33d17,
      $2eb40d81, $b7bd5c3b, $c0ba6cad, $edb88320, $9abfb3b6,
      $03b6e20c, $74b1d29a, $ead54739, $9dd277af, $04db2615,
      $73dc1683, $e3630b12, $94643b84, $0d6d6a3e, $7a6a5aa8,
      $e40ecf0b, $9309ff9d, $0a00ae27, $7d079eb1, $f00f9344,
      $8708a3d2, $1e01f268, $6906c2fe, $f762575d, $806567cb,
      $196c3671, $6e6b06e7, $fed41b76, $89d32be0, $10da7a5a,
      $67dd4acc, $f9b9df6f, $8ebeeff9, $17b7be43, $60b08ed5,
      $d6d6a3e8, $a1d1937e, $38d8c2c4, $4fdff252, $d1bb67f1,
      $a6bc5767, $3fb506dd, $48b2364b, $d80d2bda, $af0a1b4c,
      $36034af6, $41047a60, $df60efc3, $a867df55, $316e8eef,
      $4669be79, $cb61b38c, $bc66831a, $256fd2a0, $5268e236,
      $cc0c7795, $bb0b4703, $220216b9, $5505262f, $c5ba3bbe,
      $b2bd0b28, $2bb45a92, $5cb36a04, $c2d7ffa7, $b5d0cf31,
      $2cd99e8b, $5bdeae1d, $9b64c2b0, $ec63f226, $756aa39c,
      $026d930a, $9c0906a9, $eb0e363f, $72076785, $05005713,
      $95bf4a82, $e2b87a14, $7bb12bae, $0cb61b38, $92d28e9b,
      $e5d5be0d, $7cdcefb7, $0bdbdf21, $86d3d2d4, $f1d4e242,
      $68ddb3f8, $1fda836e, $81be16cd, $f6b9265b, $6fb077e1,
      $18b74777, $88085ae6, $ff0f6a70, $66063bca, $11010b5c,
      $8f659eff, $f862ae69, $616bffd3, $166ccf45, $a00ae278,
      $d70dd2ee, $4e048354, $3903b3c2, $a7672661, $d06016f7,
      $4969474d, $3e6e77db, $aed16a4a, $d9d65adc, $40df0b66,
      $37d83bf0, $a9bcae53, $debb9ec5, $47b2cf7f, $30b5ffe9,
      $bdbdf21c, $cabac28a, $53b39330, $24b4a3a6, $bad03605,
      $cdd70693, $54de5729, $23d967bf, $b3667a2e, $c4614ab8,
      $5d681b02, $2a6f2b94, $b40bbe37, $c30c8ea1, $5a05df1b,
      $2d02ef8d);

procedure updatecrc(s : pchar; len : integer);
(* update running CRC calculation with contents of a buffer *)

var
  crcl : longrec absolute crc32val;
  x : integer;

begin
  for x := 1 to len do
    begin
      crc32val := crc_32_tab[lo(crcl.lo) xor byte(s^)] xor ((crc32val 
shr 8) and $00ffffff);
      inc(s);
    end;
end;


end.
