| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT LIBRARY COMPONENTS -- |
| -- -- |
| -- S Y S T E M . C R C 3 2 -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- $Revision$ |
| -- -- |
| -- Copyright (C) 2001 Ada Core Technologies, 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; |
