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------------------------------------------------------------------------------
-- --
-- GNAT LIBRARY COMPONENTS --
-- --
-- S Y S T E M . C R C 3 2 --
-- --
-- S p e c --
-- --
-- --
-- Copyright (C) 2001 Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 2, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
-- Public License distributed with GNAT; see file COPYING. If not, write --
-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, USA. --
-- --
-- As a special exception, if other files instantiate generics from this --
-- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
-- --
-- GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). --
-- --
------------------------------------------------------------------------------
-- This package provides routines for computing a commonly used checksum
-- called CRC-32. This is a checksum based on treating the binary data
-- as a polynomial over a binary field, and the exact specifications of
-- the CRC-32 algorithm are as follows:
--
-- Name : "CRC-32"
-- Width : 32
-- Poly : 04C11DB7
-- Init : FFFFFFFF
-- RefIn : True
-- RefOut : True
-- XorOut : FFFFFFFF
-- Check : CBF43926
--
-- Note that this is the algorithm used by PKZip, Ethernet and FDDI.
--
-- For more information about this algorithm see:
--
-- ftp://ftp.rocksoft.com/papers/crc_v3.txt
-- "A Painless Guide to CRC Error Detection Algorithms", Ross N. Williams
--
-- "Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
-- of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
with Interfaces;
package System.CRC32 is
type CRC32 is new Interfaces.Unsigned_32;
-- Used to represent CRC32 values, which are 32 bit bit-strings
procedure Initialize (C : out CRC32);
pragma Inline (Initialize);
-- Initialize CRC value by assigning the standard Init value (16#FFFF_FFFF)
procedure Update
(C : in out CRC32;
Value : Character);
pragma Inline (Update);
-- Evolve CRC by including the contribution from Character'Pos (Value)
function Get_Value (C : CRC32) return Interfaces.Unsigned_32;
pragma Inline (Get_Value);
-- Get_Value computes the CRC32 value by performing an XOR with the
-- standard XorOut value (16#FFFF_FFFF). Note that this does not
-- change the value of C, so it may be used to retrieve intermediate
-- values of the CRC32 value during a sequence of Update calls.
end System.CRC32;
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