84 lines
4 KiB
Ada
84 lines
4 KiB
Ada
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------------------------------------------------------------------------------
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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) 2001-2013, 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_Warning;
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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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