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1 706 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT LIBRARY COMPONENTS                          --
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--                                                                          --
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--                        S Y S T E M  . C R C 3 2                          --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--          Copyright (C) 2001-2009, Free Software Foundation, Inc.         --
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--                                                                          --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
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--                                                                          --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception,   --
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-- version 3.1, as published by the Free Software Foundation.               --
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--                                                                          --
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-- You should have received a copy of the GNU General Public License and    --
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-- a copy of the GCC Runtime Library Exception along with this program;     --
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-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
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-- <http://www.gnu.org/licenses/>.                                          --
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--                                                                          --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc.      --
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--                                                                          --
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------------------------------------------------------------------------------
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--  This package provides routines for computing a commonly used checksum
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--  called CRC-32. This is a checksum based on treating the binary data
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--  as a polynomial over a binary field, and the exact specifications of
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--  the CRC-32 algorithm are as follows:
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--
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--     Name   : "CRC-32"
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--     Width  : 32
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--     Poly   : 04C11DB7
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--     Init   : FFFFFFFF
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--     RefIn  : True
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--     RefOut : True
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--     XorOut : FFFFFFFF
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--     Check  : CBF43926
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--
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--  Note that this is the algorithm used by PKZip, Ethernet and FDDI.
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--
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--  For more information about this algorithm see:
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--
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--  ftp://ftp.rocksoft.com/papers/crc_v3.txt
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--  "A Painless Guide to CRC Error Detection Algorithms", Ross N. Williams
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--
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--  "Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
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--  of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
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pragma Compiler_Unit;
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with Interfaces;
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package System.CRC32 is
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   type CRC32 is new Interfaces.Unsigned_32;
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   --  Used to represent CRC32 values, which are 32 bit bit-strings
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   procedure Initialize (C : out CRC32);
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   pragma Inline (Initialize);
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   --  Initialize CRC value by assigning the standard Init value (16#FFFF_FFFF)
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   procedure Update
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     (C     : in out CRC32;
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      Value : Character);
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   pragma Inline (Update);
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   --  Evolve CRC by including the contribution from Character'Pos (Value)
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   function Get_Value (C : CRC32) return Interfaces.Unsigned_32;
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   pragma Inline (Get_Value);
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   --  Get_Value computes the CRC32 value by performing an XOR with the
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   --  standard XorOut value (16#FFFF_FFFF). Note that this does not
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   --  change the value of C, so it may be used to retrieve intermediate
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   --  values of the CRC32 value during a sequence of Update calls.
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end System.CRC32;

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