type
   ByteString  = String[2];  { String representing a u8.  }
   ShortString =  String[4]; { String representing a u16. }


function ValidHexDigit(bval: Byte): Boolean;
var
   IsValid : Boolean = False;
begin
   if ((bval >= $30) and (bval <= $39)) then
      IsValid := True;
   if ((bval >= $41) and (bval <= $46)) then
      IsValid := True;
   if ((bval >= $61) and (bval <= $66)) then
      IsValid := True;

   ValidHexDigit := IsValid;
end;


function ReadDigit(bchr: Char): Byte;
var
   bval	: Byte = 0;
label
   exitearly;
begin
   bval := Byte(bchr);

   if (not ValidHexDigit(bval)) then
   begin
      bval := 0;
      goto exitearly;
   end;

   {Normalize downcase digits to upcase digits.}
   if (bchr >= 'a') then
      bval := bval xor $20;

   {Perform the conversion.}
   if (bchr >= 'A') then
      bval := (bval - $41) + 10
   else
      bval := bval - $30;

exitearly:
	  ReadDigit := bval;
end;


function ReadByte(bstr : ByteString): Byte;
var
   out : Byte = 0;
begin
   out := ReadDigit(bstr[1]) shl 4;
   out := out + ReadDigit(bstr[2]);
   ReadByte := out;
end;