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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT LIBRARY COMPONENTS --
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4 -- --
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5 -- S Y S T E M . C R C 3 2 --
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6 -- --
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7 -- S p e c --
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8 -- --
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145
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9 -- Copyright (C) 2001-2019, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package provides routines for computing a commonly used checksum
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33 -- called CRC-32. This is a checksum based on treating the binary data
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34 -- as a polynomial over a binary field, and the exact specifications of
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35 -- the CRC-32 algorithm are as follows:
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36 --
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37 -- Name : "CRC-32"
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38 -- Width : 32
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39 -- Poly : 04C11DB7
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40 -- Init : FFFFFFFF
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41 -- RefIn : True
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42 -- RefOut : True
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43 -- XorOut : FFFFFFFF
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44 -- Check : CBF43926
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45 --
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46 -- Note that this is the algorithm used by PKZip, Ethernet and FDDI.
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47 --
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48 -- For more information about this algorithm see:
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49 --
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50 -- ftp://ftp.rocksoft.com/papers/crc_v3.txt
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51
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52 -- "A Painless Guide to CRC Error Detection Algorithms", Ross N. Williams
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53 --
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54 -- "Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
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55 -- of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
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56
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57 pragma Compiler_Unit_Warning;
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58
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59 with Interfaces;
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60
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61 package System.CRC32 is
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62
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63 type CRC32 is new Interfaces.Unsigned_32;
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64 -- Used to represent CRC32 values, which are 32 bit bit-strings
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65
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66 procedure Initialize (C : out CRC32);
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67 pragma Inline (Initialize);
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68 -- Initialize CRC value by assigning the standard Init value (16#FFFF_FFFF)
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69
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70 procedure Update
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71 (C : in out CRC32;
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72 Value : Character);
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73 pragma Inline (Update);
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74 -- Evolve CRC by including the contribution from Character'Pos (Value)
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75
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76 function Get_Value (C : CRC32) return Interfaces.Unsigned_32;
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77 pragma Inline (Get_Value);
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78 -- Get_Value computes the CRC32 value by performing an XOR with the
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79 -- standard XorOut value (16#FFFF_FFFF). Note that this does not
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80 -- change the value of C, so it may be used to retrieve intermediate
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81 -- values of the CRC32 value during a sequence of Update calls.
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82
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83 end System.CRC32;
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