gcc/ada/libgnat/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) 2001-2017, 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
  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;