------------------------------------------------------------------------------ -- -- -- GNAT LIBRARY COMPONENTS -- -- -- -- S Y S T E M . C R C 3 2 -- -- -- -- S p e c -- -- -- -- Copyright (C) 2001-2009, 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 3, 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. -- -- -- -- As a special exception under Section 7 of GPL version 3, you are granted -- -- additional permissions described in the GCC Runtime Library Exception, -- -- version 3.1, as published by the Free Software Foundation. -- -- -- -- You should have received a copy of the GNU General Public License and -- -- a copy of the GCC Runtime Library Exception along with this program; -- -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- -- . -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ -- 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. pragma Compiler_Unit; 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;