Re: CRC in Ada?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 14 Nov 2013 09:39:54 -0800 (PST), david wrote:

> On Sunday, March 2, 1997 3:00:00 AM UTC-5, Dr. John B. Matthews wrote:
>> Hi! Can anyone point me to 16-bit CRC code in Ada? I've checked the
>> PAL and several other archives without luck. Any help appreciated.

From simple components:

http://www.dmitry-kazakov.de/ada/components.htm

   function Fletcher_16
            (  Data : Stream_Element_Array;
               Last : Stream_Element_Offset
            )  return Stream_Element_Array is
      Sum_1 : Unsigned_16 := 16#FF#;
      Sum_2 : Unsigned_16 := 16#FF#;
      Index : Stream_Element_Offset := Data'First;
   begin
      for Major in 1..(Last - Data'First + 1) / 21 loop
         for Index in Major * 21 - 20..Major * 21 loop
            Sum_1 := Sum_1 + Unsigned_16 (Data (Index));
            Sum_2 := Sum_2 + Sum_1;
         end loop;
         Sum_1 := (Sum_1 and 16#FF#) + Sum_1 / 2**8;
         Sum_2 := (Sum_2 and 16#FF#) + Sum_2 / 2**8;
      end loop;
      Sum_1 := (Sum_1 and 16#FF#) + Sum_1 / 2**8;
      Sum_2 := (Sum_2 and 16#FF#) + Sum_2 / 2**8;
      return
      (  1 => Stream_Element (Sum_1 and 16#FF#),
         2 => Stream_Element (Sum_2 and 16#FF#)
      );
   end Fletcher_16;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de