I need to calculate Crc16 checksums with a $1021 polynom over large files, below

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Asked: May 17, 20262026-05-17T01:57:10+00:00 2026-05-17T01:57:10+00:00

I need to calculate Crc16 checksums with a $1021 polynom over large files, below

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I need to calculate Crc16 checksums with a $1021 polynom over large files, below is my current implementation but it’s rather slow on large files (eg a 90 MB file takes about 9 seconds).

So my question is how to improve my current implementation (to make it faster), I have googled and looked at some samples implementing a table lookup but my problem is that I don’t understand how to modify them to include the polynom (probably my math is failing).

{ based on http://miscel.dk/MiscEl/CRCcalculations.html }
function Crc16(const Buffer: PByte; const BufSize: Int64;
  const Polynom: WORD=$1021; const Seed: WORD=0): Word;
var
  i,j: Integer;
begin
  Result := Seed;

  for i:=0 to BufSize-1 do
  begin
    Result := Result xor (Buffer[i] shl 8);

    for j:=0 to 7 do begin
      if (Result and $8000) <> 0 then
        Result := (Result shl 1) xor Polynom
      else Result := Result shl 1;
    end;
  end;

  Result := Result and $FFFF;
end;