Código Delphi [-]
Library CRC;

uses
   SysUtils, Classes, Dialogs, StrUtils, Math;

{$R *.res}

function Crc16(Buffer : String; Polynom, Initial : Cardinal) : Cardinal;
var
   i,j : Integer;

begin
   Result := Initial;
   for i := 1 to Length(Buffer) do
   begin
      Result := Result xor ord(buffer[i]);
      for j := 0 to 7 do
      begin
         if (Result and $0001) <> 0 then
            Result := (Result shr 1) xor Polynom
         else
            Result := Result shr 1;
      end;
   end;
end;

function ComputeChecksum(Buffer : PChar) : Cardinal; stdcall;
var
   i : Cardinal;
   CrcTable : Array[0..255] of Cardinal;

begin

   for i := 0 to 255 do
      CrcTable[i] := Crc16(chr(i), $A001, 0);

   Result := 0;

   for i := 1 to Length(Buffer) do
     Result := (Result shr 8) xor CrcTable[(ord(Buffer[i]) xor Result) and $ff];

end;

exports
   ComputeChecksum;

end.

Código Delphi [-]
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    Label1: TLabel;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  function ComputeChecksum(Buffer : PChar) : Cardinal; StdCall; external 'CRC.dll';

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
   ShowMessage(IntToStr(ComputeChecksum(PChar(Edit1.Text))));
end;

end.