File : s-crc32.ads
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) 2001-2013, 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 -- --
19 -- --
20 -- --
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
57 pragma Compiler_Unit_Warning;
58
59 with Interfaces;
60
61 package 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
83 end System.CRC32;