CRC8 String Calculating

Unit CRC8.pas

unit Crc8;

interface

{unit Crc8.pas}

Uses
Classes, Windows;

Function Crc_8n(p : array of BYTE; len : BYTE) : Byte;

implementation

Function Crc_8n(p : array of BYTE; len : BYTE) : Byte;
Var
	j, cbit, aout, crc, crc_a, crc_b : Byte;
	i : integer;
begin
	crc := 0;
	i := 0;

// Take the shifted bit
	repeat
		crc_a := p[i];
		inc(i);
		j := 8;
		cbit := 1;
			repeat
			crc_b := crc_a;
			crc_b := crc_b xor crc; 
			aout := crc_b and cbit;
			if aout<>0 then begin
			crc := crc xor $18; 
			crc := crc shr 1;
			crc := crc or $80;
	end else begin
	crc := crc shr 1;
	end;
crc_a := crc_a shr 1;
dec(j);
until j = 0;
dec(len);
until len = 0;

result := crc;
end;

end.

Funktion:

uses CRC8

const MinBase = 2; 
      MaxBase = 36;

//

Function strtonum (const S: string; base: integer;
Neg: Boolean; max: integer): integer;
var negate, done: Boolean;
    I, Len, digit, MMB: integer;
    C: Char;
    Mdb, Res: integer;
Begin
   Res := 0; I:= 1; digit:= 0;
    If (base >= minbase) and (base <= maxbase) then begin
    MMB:= max mod base;
    MDB:= max Div base;
    Len:= length (s );
    Negate:= false;
     While (I <= Len) and (S [I] = '') Do Inc (I );
      If neg then begin
       Case s[I] of '+': Inc (I );
       '-': Begin Inc (I); negate:= true; end;
     End; (* case *)
    End; (* If neg *)
  Done:= Len> I;
    While (I <= Len) and done do begin
    C:= upcase (s [I]);
     Case C  of
      '0' .. '9': digit:= ord (c)-48;
      'A' .. 'Z': digit:= ord (c)-55;
    Else done:= false
  End; (* case *)
  Done:= Done And (digit <base );
    If done then begin
     Done:= (RES <MDB) or (RES = MDB) and (digit <= MMB );
       If done then begin
         Res:= res * base + digit;
         INC (I );
       End; (* if done *)
    End; (* if done *)
   End; (* While *)
  If negate then res:=-res;
 End; (* if done *)
Result:= res;
End;

Beispiel :

procedure TForm1.Button1Click(Sender: TObject);
Var S : String; P : Array[0..255] of Byte;
    Len : Byte; R : Byte; I : Integer;
begin
  S := Edit1.Text;
  if length(s) mod 2 = 1 then s := s + '0';
  	Memo1.Lines.Add(S + ':');
  		for i:=1 to length(s) div 2 do begin
  		p[i-1] := BYTE(StrToNum(copy(s, (i-1)*2 + 1, 2), 16, false, 500));
  	Memo1.Lines.Add(IntToStr(I) + '--> ' + IntToHex(p[i-1], 2));
  end;

  Len := length(s) div 2;
  R := Crc_8n(P, Len);
  Memo1.Lines.Add('Crc8 Result:' + IntToHex(R, 2));
end;