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Newsgroups: comp.lang.ada
Subject: Re: crc and Ada
References: <slrnbcec3j.rh.swierczu@staticline881.toya.net.pl>
From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: 19 May 2003 11:09:27 +0200
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Date: 2003-05-19T11:09:27+02:00
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Bart�omiej �. <swierczu@wpk.p.lodz.pl> writes:

> Hello,
> I'm starting in Ada, and I can't use same operators (like xor, and) in
> my programs. I need to count crc. In Java I was writting:

If your compiler is GNAT, there is the package System.CRC32.  Look at
the sources in lib/gcc-lib/.../.../adainclude/s-crc32.ad{b,s}.

There is also an older version of this file at:

http://korea.gnu.org/gcc/src/gcc-3.1/gcc/ada/s-crc32.adb
http://korea.gnu.org/gcc/src/gcc-3.1/gcc/ada/s-crc32.ads

FWIW, consider the following code:

type CRC32 is new Interfaces.Unsigned_32;
--  Used to represent CRC32 values, which are 32 bit bit-strings


procedure Update (C : in out CRC32; Value : Character) is
   V : constant CRC32 := CRC32 (Character'Pos (Value));
begin
   C := Shift_Right (C, 8) xor Table (V xor (C and 16#0000_00FF#));
end Update;

HTH

--
Ludovic Brenta.