gcc/ada/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 --                            $Revision$
  10 --                                                                          --
  11 --              Copyright (C) 2001 Ada Core Technologies, Inc.              --
  12 --                                                                          --
  13 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  16 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com).   --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 --  This package provides routines for computing a commonly used checksum
  36 --  called CRC-32. This is a checksum based on treating the binary data
  37 --  as a polynomial over a binary field, and the exact specifications of
  38 --  the CRC-32 algorithm are as follows:
  39 --
  40 --     Name   : "CRC-32"
  41 --     Width  : 32
  42 --     Poly   : 04C11DB7
  43 --     Init   : FFFFFFFF
  44 --     RefIn  : True
  45 --     RefOut : True
  46 --     XorOut : FFFFFFFF
  47 --     Check  : CBF43926
  48 --
  49 --  Note that this is the algorithm used by PKZip, Ethernet and FDDI.
  50 --
  51 --  For more information about this algorithm see:
  52 --
  53 --  ftp://ftp.rocksoft.com/papers/crc_v3.txt
  54
  55 --  "A Painless Guide to CRC Error Detection Algorithms", Ross N. Williams
  56 --
  57 --  "Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
  58 --  of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
  59
  60 with Interfaces;
  61
  62 package System.CRC32 is
  63
  64    type CRC32 is new Interfaces.Unsigned_32;
  65    --  Used to represent CRC32 values, which are 32 bit bit-strings
  66
  67    procedure Initialize (C : out CRC32);
  68    pragma Inline (Initialize);
  69    --  Initialize CRC value by assigning the standard Init value (16#FFFF_FFFF)
  70
  71    procedure Update
  72      (C     : in out CRC32;
  73       Value : Character);
  74    pragma Inline (Update);
  75    --  Evolve CRC by including the contribution from Character'Pos (Value)
  76
  77    function Get_Value (C : CRC32) return Interfaces.Unsigned_32;
  78    pragma Inline (Get_Value);
  79    --  Get_Value computes the CRC32 value by performing an XOR with the
  80    --  standard XorOut value (16#FFFF_FFFF). Note that this does not
  81    --  change the value of C, so it may be used to retrieve intermediate
  82    --  values of the CRC32 value during a sequence of Update calls.
  83
  84 end System.CRC32;