unit cksumunit;

{$mode objfpc}{$H+}

interface

//CkSum compatible CRC32 function
function CkSum(sum: longword; buf: PByte; len: longword): longword;

implementation

const
  cksum_table: array[byte] of longword = (
  $00000000,
  $04c11db7, $09823b6e, $0d4326d9, $130476dc, $17c56b6b,
  $1a864db2, $1e475005, $2608edb8, $22c9f00f, $2f8ad6d6,
  $2b4bcb61, $350c9b64, $31cd86d3, $3c8ea00a, $384fbdbd,
  $4c11db70, $48d0c6c7, $4593e01e, $4152fda9, $5f15adac,
  $5bd4b01b, $569796c2, $52568b75, $6a1936c8, $6ed82b7f,
  $639b0da6, $675a1011, $791d4014, $7ddc5da3, $709f7b7a,
  $745e66cd, $9823b6e0, $9ce2ab57, $91a18d8e, $95609039,
  $8b27c03c, $8fe6dd8b, $82a5fb52, $8664e6e5, $be2b5b58,
  $baea46ef, $b7a96036, $b3687d81, $ad2f2d84, $a9ee3033,
  $a4ad16ea, $a06c0b5d, $d4326d90, $d0f37027, $ddb056fe,
  $d9714b49, $c7361b4c, $c3f706fb, $ceb42022, $ca753d95,
  $f23a8028, $f6fb9d9f, $fbb8bb46, $ff79a6f1, $e13ef6f4,
  $e5ffeb43, $e8bccd9a, $ec7dd02d, $34867077, $30476dc0,
  $3d044b19, $39c556ae, $278206ab, $23431b1c, $2e003dc5,
  $2ac12072, $128e9dcf, $164f8078, $1b0ca6a1, $1fcdbb16,
  $018aeb13, $054bf6a4, $0808d07d, $0cc9cdca, $7897ab07,
  $7c56b6b0, $71159069, $75d48dde, $6b93dddb, $6f52c06c,
  $6211e6b5, $66d0fb02, $5e9f46bf, $5a5e5b08, $571d7dd1,
  $53dc6066, $4d9b3063, $495a2dd4, $44190b0d, $40d816ba,
  $aca5c697, $a864db20, $a527fdf9, $a1e6e04e, $bfa1b04b,
  $bb60adfc, $b6238b25, $b2e29692, $8aad2b2f, $8e6c3698,
  $832f1041, $87ee0df6, $99a95df3, $9d684044, $902b669d,
  $94ea7b2a, $e0b41de7, $e4750050, $e9362689, $edf73b3e,
  $f3b06b3b, $f771768c, $fa325055, $fef34de2, $c6bcf05f,
  $c27dede8, $cf3ecb31, $cbffd686, $d5b88683, $d1799b34,
  $dc3abded, $d8fba05a, $690ce0ee, $6dcdfd59, $608edb80,
  $644fc637, $7a089632, $7ec98b85, $738aad5c, $774bb0eb,
  $4f040d56, $4bc510e1, $46863638, $42472b8f, $5c007b8a,
  $58c1663d, $558240e4, $51435d53, $251d3b9e, $21dc2629,
  $2c9f00f0, $285e1d47, $36194d42, $32d850f5, $3f9b762c,
  $3b5a6b9b, $0315d626, $07d4cb91, $0a97ed48, $0e56f0ff,
  $1011a0fa, $14d0bd4d, $19939b94, $1d528623, $f12f560e,
  $f5ee4bb9, $f8ad6d60, $fc6c70d7, $e22b20d2, $e6ea3d65,
  $eba91bbc, $ef68060b, $d727bbb6, $d3e6a601, $dea580d8,
  $da649d6f, $c423cd6a, $c0e2d0dd, $cda1f604, $c960ebb3,
  $bd3e8d7e, $b9ff90c9, $b4bcb610, $b07daba7, $ae3afba2,
  $aafbe615, $a7b8c0cc, $a379dd7b, $9b3660c6, $9ff77d71,
  $92b45ba8, $9675461f, $8832161a, $8cf30bad, $81b02d74,
  $857130c3, $5d8a9099, $594b8d2e, $5408abf7, $50c9b640,
  $4e8ee645, $4a4ffbf2, $470cdd2b, $43cdc09c, $7b827d21,
  $7f436096, $7200464f, $76c15bf8, $68860bfd, $6c47164a,
  $61043093, $65c52d24, $119b4be9, $155a565e, $18197087,
  $1cd86d30, $029f3d35, $065e2082, $0b1d065b, $0fdc1bec,
  $3793a651, $3352bbe6, $3e119d3f, $3ad08088, $2497d08d,
  $2056cd3a, $2d15ebe3, $29d4f654, $c5a92679, $c1683bce,
  $cc2b1d17, $c8ea00a0, $d6ad50a5, $d26c4d12, $df2f6bcb,
  $dbee767c, $e3a1cbc1, $e760d676, $ea23f0af, $eee2ed18,
  $f0a5bd1d, $f464a0aa, $f9278673, $fde69bc4, $89b8fd09,
  $8d79e0be, $803ac667, $84fbdbd0, $9abc8bd5, $9e7d9662,
  $933eb0bb, $97ffad0c, $afb010b1, $ab710d06, $a6322bdf,
  $a2f33668, $bcb4666d, $b8757bda, $b5365d03, $b1f740b4
  );

function CkSum(sum: longword; buf: PByte; len: longword): longword;
var i: longword;
begin
  if buf=nil then
    exit(0);

  //Calculating data CRC
  for i:=0 to len-1 do
  begin
    sum:=(sum shl 8) xor cksum_table[((sum shr 24) xor buf^) and $FF];
    inc(buf);
  end;

  //Adding data length to CRC
  while len>0 do
  begin
    sum:=(sum shl 8) xor cksum_table[((sum shr 24) xor len) and $FF];
    len:=len shr 8;
  end;

  Result:=not sum;
end;

end.