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annotate m-toolbox/classes/+utils/@helper/dzip.m @ 0:f0afece42f48

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Import.
author Daniele Nicolodi <nicolodi@science.unitn.it>
date Wed, 23 Nov 2011 19:22:13 +0100
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Daniele Nicolodi <nicolodi@science.unitn.it>
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1 function Z = dzip(M)
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Daniele Nicolodi <nicolodi@science.unitn.it>
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2 % DZIP - losslessly compress data into smaller memory space
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Daniele Nicolodi <nicolodi@science.unitn.it>
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3 %
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Daniele Nicolodi <nicolodi@science.unitn.it>
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4 % USAGE:
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Daniele Nicolodi <nicolodi@science.unitn.it>
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5 % Z = dzip(M)
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Daniele Nicolodi <nicolodi@science.unitn.it>
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6 %
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Daniele Nicolodi <nicolodi@science.unitn.it>
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7 % VARIABLES:
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Daniele Nicolodi <nicolodi@science.unitn.it>
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8 % M = variable to compress
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Daniele Nicolodi <nicolodi@science.unitn.it>
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9 % Z = compressed output
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Daniele Nicolodi <nicolodi@science.unitn.it>
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10 %
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Daniele Nicolodi <nicolodi@science.unitn.it>
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11 % NOTES: (1) The input variable M can be a scalar, vector, matrix, or
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Daniele Nicolodi <nicolodi@science.unitn.it>
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12 % n-dimensional matrix
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Daniele Nicolodi <nicolodi@science.unitn.it>
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13 % (2) The input variable must be a non-complex and full (meaning
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Daniele Nicolodi <nicolodi@science.unitn.it>
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14 % matrices declared as type "sparse" are not allowed)
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Daniele Nicolodi <nicolodi@science.unitn.it>
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15 % (3) Permitted input types include: double, single, logical,
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Daniele Nicolodi <nicolodi@science.unitn.it>
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16 % char, int8, uint8, int16, uint16, int32, uint32, int64,
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Daniele Nicolodi <nicolodi@science.unitn.it>
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17 % and uint64.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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18 % (4) In testing, DZIP compresses several megabytes of data per
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Daniele Nicolodi <nicolodi@science.unitn.it>
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19 % second.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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20 % (5) In testing, random matrices of type double compress to about
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Daniele Nicolodi <nicolodi@science.unitn.it>
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21 % 75% of their original size. Sparsely populated matrices or
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Daniele Nicolodi <nicolodi@science.unitn.it>
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22 % matrices with regular structure can compress to less than
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Daniele Nicolodi <nicolodi@science.unitn.it>
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23 % 1% of their original size. The realized compression ratio
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Daniele Nicolodi <nicolodi@science.unitn.it>
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24 % is heavily dependent on the data.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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25 % (6) Variables originally occupying very little memory (less than
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Daniele Nicolodi <nicolodi@science.unitn.it>
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26 % about half of one kilobyte) are handled correctly, but
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Daniele Nicolodi <nicolodi@science.unitn.it>
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27 % the compression requires some overhead and may actually
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Daniele Nicolodi <nicolodi@science.unitn.it>
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28 % increase the storage size of such small data sets.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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29 % One exception to this rule is noted below.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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30 % (7) LOGICAL variables are compressed to a small fraction of
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Daniele Nicolodi <nicolodi@science.unitn.it>
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31 % their original sizes.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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32 % (8) The DUNZIP function decompresses the output of this function
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Daniele Nicolodi <nicolodi@science.unitn.it>
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33 % and restores the original data, including size and class type.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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34 % (9) This function uses the public domain ZLIB Deflater algorithm.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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35 % (10) Carefully tested, but no warranty; use at your own risk.
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Daniele Nicolodi <nicolodi@science.unitn.it>
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36 % (11) Michael Kleder, Nov 2005
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Daniele Nicolodi <nicolodi@science.unitn.it>
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37
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Daniele Nicolodi <nicolodi@science.unitn.it>
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38 s = size(M);
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Daniele Nicolodi <nicolodi@science.unitn.it>
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39 c = class(M);
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Daniele Nicolodi <nicolodi@science.unitn.it>
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40 cn = strmatch(c,{'double','single','logical','char','int8','uint8',...
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Daniele Nicolodi <nicolodi@science.unitn.it>
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41 'int16','uint16','int32','uint32','int64','uint64'});
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Daniele Nicolodi <nicolodi@science.unitn.it>
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42 if cn == 3 | cn == 4
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Daniele Nicolodi <nicolodi@science.unitn.it>
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43 M=uint8(M);
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Daniele Nicolodi <nicolodi@science.unitn.it>
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44 end
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Daniele Nicolodi <nicolodi@science.unitn.it>
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45 M=typecast(M(:),'uint8');
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Daniele Nicolodi <nicolodi@science.unitn.it>
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46 M=[uint8(cn);uint8(length(s));typecast(s(:),'uint8');M(:)];
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Daniele Nicolodi <nicolodi@science.unitn.it>
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47 f=java.io.ByteArrayOutputStream();
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Daniele Nicolodi <nicolodi@science.unitn.it>
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48 g=java.util.zip.DeflaterOutputStream(f);
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Daniele Nicolodi <nicolodi@science.unitn.it>
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49 g.write(M);
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Daniele Nicolodi <nicolodi@science.unitn.it>
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50 g.close;
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Daniele Nicolodi <nicolodi@science.unitn.it>
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51 Z=typecast(f.toByteArray,'uint8');
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Daniele Nicolodi <nicolodi@science.unitn.it>
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52 f.close;
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Daniele Nicolodi <nicolodi@science.unitn.it>
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53 return