1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT LIBRARY COMPONENTS                          --
4--                                                                          --
5--                        S Y S T E M  . C R C 3 2                          --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 2001-2021, Free Software Foundation, Inc.         --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  This package provides routines for computing a commonly used checksum
33--  called CRC-32. This is a checksum based on treating the binary data
34--  as a polynomial over a binary field, and the exact specifications of
35--  the CRC-32 algorithm are as follows:
36--
37--     Name   : "CRC-32"
38--     Width  : 32
39--     Poly   : 04C11DB7
40--     Init   : FFFFFFFF
41--     RefIn  : True
42--     RefOut : True
43--     XorOut : FFFFFFFF
44--     Check  : CBF43926
45--
46--  Note that this is the algorithm used by PKZip, Ethernet and FDDI.
47--
48--  For more information about this algorithm see:
49--
50--  ftp://ftp.rocksoft.com/papers/crc_v3.txt
51
52--  "A Painless Guide to CRC Error Detection Algorithms", Ross N. Williams
53--
54--  "Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
55--  of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
56
57pragma Compiler_Unit_Warning;
58
59with Interfaces;
60
61package System.CRC32 is
62
63   type CRC32 is new Interfaces.Unsigned_32;
64   --  Used to represent CRC32 values, which are 32 bit bit-strings
65
66   procedure Initialize (C : out CRC32);
67   pragma Inline (Initialize);
68   --  Initialize CRC value by assigning the standard Init value (16#FFFF_FFFF)
69
70   procedure Update
71     (C     : in out CRC32;
72      Value : Character);
73   pragma Inline (Update);
74   --  Evolve CRC by including the contribution from Character'Pos (Value)
75
76   function Get_Value (C : CRC32) return Interfaces.Unsigned_32;
77   pragma Inline (Get_Value);
78   --  Get_Value computes the CRC32 value by performing an XOR with the
79   --  standard XorOut value (16#FFFF_FFFF). Note that this does not
80   --  change the value of C, so it may be used to retrieve intermediate
81   --  values of the CRC32 value during a sequence of Update calls.
82
83end System.CRC32;
84