miniADSB receiver project - CRC calculation

Thread: http://www.mikrocontroller.net/topic/135459#new

  EUROCONTROL - CRC Calculation for Mode-S Transponders

Generic implementation in Pascal 

function parity112bit(st:string):string;
const poly:cardinal=FFFA0480;
var i,data,data1,data2:cardinal;
begin
       result:=000000;
       if length(st)<>11 then exit;
       data:=(ord(st[1])shl 24) OR (ord (st[2])shl 16) OR
        (ord (st[3])shl 8) or (ord(st[4]));
       data1:=(ord(st[5])shl 24) OR (ord (st[6])shl 16) OR
        (ord (st[7])shl 8) or (ord(st[8]));
       data2:=(ord(st[9])shl 24) OR (ord (st[10])shl 16) OR
        (ord (st[11])shl 8);

       for i:=1 to 88 do
       begin
          if (data and 80000000) <> 0 then
                data:=data xor poly;
          data:=data shl 1;
          if (data1 and 80000000) <>0 then data:=data or 1;
          data1:=data1 shl 1;
          if (data2 and 80000000) <>0 then data1:=data1 or 1;
          data2:=data2 shl 1;
       end;
       result:=copy(inttohex(data,8),1,6);
end;

function parity56bit(st:string):string;
const poly:cardinal=FFFA0480;
var i,data,data1:cardinal;
begin
       result:=000000;
       if length(st)<>4 then exit;
       data:=(ord(st[1])shl 24) OR (ord (st[2])shl 16) OR
        (ord (st[3])shl 8) or (ord(st[4]));
       for i:=1 to 32 do
       begin
          if (data and 80000000) <> 0 then
                data:=data xor poly;
          data:=data shl 1;
       end;
       result:=copy(inttohex(data,8),1,6);
end;

Implementation for AVR processors