1 ------------------------------------------------------------------------------
3 -- GNAT LIBRARY COMPONENTS --
5 -- G N A T . C R C 3 2 --
9 -- Copyright (C) 2001 Ada Core Technologies, Inc. --
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, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
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. --
29 -- GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). --
31 ------------------------------------------------------------------------------
33 -- This package provides routines for computing a commonly used checksum
34 -- called CRC-32. This is a checksum based on treating the binary data
35 -- as a polynomial over a binary field, and the exact specifications of
36 -- the CRC-32 algorithm are as follows:
47 -- Note that this is the algorithm used by PKZip, Ethernet and FDDI.
49 -- For more information about this algorithm see:
51 -- ftp://ftp.rocksoft.com/papers/crc_v3.txt
53 -- "A Painless Guide to CRC Error Detection Algorithms", Ross N. Williams
55 -- "Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
56 -- of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
64 subtype CRC32
is System
.CRC32
.CRC32
;
65 -- Used to represent CRC32 values, which are 32 bit bit-strings
67 procedure Initialize
(C
: out CRC32
)
68 renames System
.CRC32
.Initialize
;
69 -- Initialize CRC value by assigning the standard Init value (16#FFFF_FFFF)
74 renames System
.CRC32
.Update
;
75 -- Evolve CRC by including the contribution from Character'Pos (Value)
80 pragma Inline
(Update
);
81 -- For each character in the Value string call above routine
85 Value
: Wide_Character);
86 pragma Inline
(Update
);
87 -- Evolve CRC by including the contribution from Wide_Character'Pos (Value)
88 -- with the bytes being included in the natural memory order.
93 pragma Inline
(Update
);
94 -- For each character in the Value string call above routine
98 Value
: Ada
.Streams
.Stream_Element
);
99 pragma Inline
(Update
);
100 -- Evolve CRC by including the contribution from Value
104 Value
: Ada
.Streams
.Stream_Element_Array
);
105 pragma Inline
(Update
);
106 -- For each element in the Value array call above routine
108 function Get_Value
(C
: CRC32
) return Interfaces
.Unsigned_32
109 renames System
.CRC32
.Get_Value
;
110 -- Get_Value computes the CRC32 value by performing an XOR with the
111 -- standard XorOut value (16#FFFF_FFFF). Note that this does not
112 -- change the value of C, so it may be used to retrieve intermediate
113 -- values of the CRC32 value during a sequence of Update calls.