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   1  --  Just for fun, playing with the old Zip "Reduce" format...
   2  --
   3  --  "Reduce" combines the LZ77 method with a probabilistic
   4  --  predictor using a Markov chain.
   5  --
   6  --  The format has a single block, then a single matrix,
   7  --  for the whole data to be compressed :-(.
   8  --
   9  --  NB: this compressor works in two passes, the first pass
  10  --     serving to compute the exact optimal Markov matrix for the whole
  11  --     data to be compressed. Hence, it is slow. However,
  12  --     we cache the last n=LZ_cache_size bytes compressed by LZ77.
  13  --     The resulting compression is optimal within the constraints of the
  14  --     "Reduce" format (one block, poor encoding of compressed data and of the
  15  --     compression structure itself (the Markov matrix)).
  16  --
  17  --  Author: G. de Montmollin, January 2009
  18  --
  19  --  Legal licensing note:
  20  
  21  --  Copyright (c) 2009 .. 2023 Gautier de Montmollin
  22  --  SWITZERLAND
  23  
  24  --  Permission is hereby granted, free of charge, to any person obtaining a copy
  25  --  of this software and associated documentation files (the "Software"), to deal
  26  --  in the Software without restriction, including without limitation the rights
  27  --  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  28  --  copies of the Software, and to permit persons to whom the Software is
  29  --  furnished to do so, subject to the following conditions:
  30  
  31  --  The above copyright notice and this permission notice shall be included in
  32  --  all copies or substantial portions of the Software.
  33  
  34  --  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  35  --  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  36  --  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  37  --  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  38  --  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  39  --  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  40  --  THE SOFTWARE.
  41  
  42  --  NB: this is the MIT License, as found on the site
  43  --  http://www.opensource.org/licenses/mit-license.php
  44  
  45  with Zip.CRC_Crypto;
  46  
  47  private procedure Zip.Compress.Reduce
  48    (input,
  49     output           : in out Zip_Streams.Root_Zipstream_Type'Class;
  50     input_size_known :        Boolean;
  51     input_size       :        Zip_64_Data_Size_Type;  --  ignored if unknown
  52     feedback         :        Feedback_Proc;
  53     method           :        Reduction_Method;
  54     CRC              : in out Interfaces.Unsigned_32;  --  only updated here
  55     crypto           : in out CRC_Crypto.Crypto_pack;
  56     output_size      :    out Zip_64_Data_Size_Type;
  57     compression_ok   :    out Boolean);  --  indicates when compressed <= uncompressed