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annotate BitDecoder.hpp @ 27:95a10553ff90

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Optimize BitDecoder, and refactor functions that are not timecritical out of header.
author Tom Fredrik Blenning Klaussen <bfg@blenning.no>
date Thu, 06 Sep 2012 18:20:11 +0200
parents 754e12c927b3
children f711ddb56ae7
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754e12c927b3 Class for decoding binary datarepresentations, eg. Huffman trees.
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1 #ifndef BITDECODER_HPP
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2 #define BITDECODER_HPP
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3
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4 #include <QtCore/QBitArray>
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5 #include <QtCore/QString>
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6 #include <QtCore/QMap>
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7
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8 class BitDecoder {
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9 BitDecoder* low;
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10 BitDecoder* high;
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11 QString _data;
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12
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13 private:
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14 BitDecoder(BitDecoder* low_in, BitDecoder* high_in);
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16 uint decode(QString& resString, const QBitArray& bits, uint offset)
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17 {
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18 //Data is always stored in a leaf node.
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19 if (high) {
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20 return (bits.testBit(offset) ? high : low)->decode(resString, bits, offset + 1) + 1;
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21 }
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22 else {
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23 resString.append(_data);
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24 return 1;
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25 }
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26 }
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28 public:
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29 BitDecoder(const QString& d);
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30 ~BitDecoder();
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31 const QString& data() const;
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32
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33 QString decode(const QBitArray& bits)
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34 {
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35 QString combined;
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36 uint n = bits.size();
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37 //Just a qualified overestimate guess on what we will need.
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38 combined.reserve(n/4);
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39 for (uint decodedBits = 0; decodedBits < n; decodedBits += decode(combined, bits, decodedBits) - 1);
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40 combined.squeeze();
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41 return combined;
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42 }
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43
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44 static BitDecoder* merge(BitDecoder* low, BitDecoder* high);
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45 static QBitArray unite(const QBitArray& first, const QBitArray& second)
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46 {
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47 int n = first.size();
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48 int n2 = second.size();
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49 QBitArray result(n + n2);
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50 for (int i = 0; i < n; ++i) {
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51 result.setBit(i, first.testBit(i));
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52 }
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53 for (int i = 0; i < n2; ++i) {
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54 result.setBit(n + i, second.testBit(i));
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55 }
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56 return result;
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57 }
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60 QMap<QString, QBitArray> createEncoder() const;
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61 };
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63 #endif //BITDECODER_HPP