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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT LIBRARY COMPONENTS --
4 -- --
5 -- G N A T . C R C 3 2 --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 2004-2005, AdaCore --
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 2, 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. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
20 -- Boston, MA 02110-1301, USA. --
21 -- --
22 -- As a special exception, if other files instantiate generics from this --
23 -- unit, or you link this unit with other files to produce an executable, --
24 -- this unit does not by itself cause the resulting executable to be --
25 -- covered by the GNU General Public License. This exception does not --
26 -- however invalidate any other reasons why the executable file might be --
27 -- covered by the GNU Public License. --
28 -- --
29 -- GNAT was originally developed by the GNAT team at New York University. --
30 -- Extensive contributions were provided by Ada Core Technologies Inc. --
31 -- --
32 ------------------------------------------------------------------------------
34 -- This package provides routines for computing a commonly used checksum
35 -- called CRC-32. This is a checksum based on treating the binary data
36 -- as a polynomial over a binary field, and the exact specifications of
37 -- the CRC-32 algorithm are as follows:
39 -- Name : "CRC-32"
40 -- Width : 32
41 -- Poly : 04C11DB7
42 -- Init : FFFFFFFF
43 -- RefIn : True
44 -- RefOut : True
45 -- XorOut : FFFFFFFF
46 -- Check : CBF43926
48 -- Note that this is the algorithm used by PKZip, Ethernet and FDDI
50 -- For more information about this algorithm see:
52 -- ftp://ftp.rocksoft.com/papers/crc_v3.txt
54 -- "A Painless Guide to CRC Error Detection Algorithms", Ross N. Williams
56 -- "Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
57 -- of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
59 with Ada.Streams;
60 with Interfaces;
61 with System.CRC32;
63 package GNAT.CRC32 is
65 subtype CRC32 is System.CRC32.CRC32;
66 -- Used to represent CRC32 values, which are 32 bit bit-strings
68 procedure Initialize (C : out CRC32)
69 renames System.CRC32.Initialize;
70 -- Initialize CRC value by assigning the standard Init value (16#FFFF_FFFF)
72 procedure Update
73 (C : in out CRC32;
74 Value : Character)
75 renames System.CRC32.Update;
76 -- Evolve CRC by including the contribution from Character'Pos (Value)
78 procedure Update
79 (C : in out CRC32;
80 Value : String);
81 -- For each character in the Value string call above routine
83 procedure Wide_Update
84 (C : in out CRC32;
85 Value : Wide_Character);
86 -- Evolve CRC by including the contribution from Wide_Character'Pos (Value)
87 -- with the bytes being included in the natural memory order.
89 procedure Wide_Update
90 (C : in out CRC32;
91 Value : Wide_String);
92 -- For each character in the Value string call above routine
94 procedure Update
95 (C : in out CRC32;
96 Value : Ada.Streams.Stream_Element);
97 -- Evolve CRC by including the contribution from Value
99 procedure Update
100 (C : in out CRC32;
101 Value : Ada.Streams.Stream_Element_Array);
102 -- For each element in the Value array call above routine
104 function Get_Value (C : CRC32) return Interfaces.Unsigned_32
105 renames System.CRC32.Get_Value;
106 -- Get_Value computes the CRC32 value by performing an XOR with the
107 -- standard XorOut value (16#FFFF_FFFF). Note that this does not
108 -- change the value of C, so it may be used to retrieve intermediate
109 -- values of the CRC32 value during a sequence of Update calls.
111 pragma Inline (Update);
112 pragma Inline (Wide_Update);
113 end GNAT.CRC32;