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Java Source format, 1 year 3 weeks old, and 202 hits.

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Wednesday, May 23rd, 2012 at 4:52:01pm MDT 

  1. package TDC.Compression.Arithmetic;
  2.  
  3. /**
  4. * Excluding Adaptive Unigram Model {
  5. * @author Inna Tuzhikova
  6. */
  7. final class ExcludingAdaptiveUnigramModel {
  8.  
  9.     /**
  10.      * Construct an excluding adaptive unigram model.
  11.      */
  12.     public ExcludingAdaptiveUnigramModel() {
  13.         _count = new int[257];
  14.         java.util.Arrays.fill(_count, 1); // counts are non-cumulative
  15.     }
  16.  
  17.     /**
  18.      * Compute the resulting interval to code the specified symbol given the
  19.      * specified excluded bytes.
  20.      *
  21.      * @param symbol Symbol to code.
  22.      * @param result Interval to code the symbol.
  23.      * @param exclusions Bytes to exclude as possible outcomes for interval.
  24.      */
  25.     public void interval(int symbol, int[] result, ByteSet exclusions) {
  26.         if (symbol == ArithCodeModel.EOF) {
  27.             symbol = EOF_INDEX;
  28.         }
  29.         int sum = 0;
  30.         for (int i = 0; i < symbol; ++i) {
  31.             if (!exclusions.contains(i)) {
  32.                 sum += _count[i];
  33.             }
  34.         }
  35.         result[0] = sum;
  36.         sum += _count[symbol];
  37.         result[1] = sum;
  38.         for (int i = symbol + 1; i < _count.length - 1; ++i) {
  39.             if (!exclusions.contains(i)) {
  40.                 sum += _count[i];
  41.             }
  42.         }
  43.         if (symbol != EOF_INDEX) {
  44.             sum += _count[EOF_INDEX];
  45.         }
  46.         result[2] = sum;
  47.         increment(symbol);
  48.     }
  49.  
  50.     /**
  51.      * Return the symbol corresponding to the specified count, given the
  52.      * specified excluded bytes.
  53.      *
  54.      * @param midCount Count of symbol to return.
  55.      * @param exclusions Bytes to exclude from consideration.
  56.      * @return Symbol represented by specified count.
  57.      */
  58.     public int pointToSymbol(int midCount, ByteSet exclusions) {
  59.         int sum = 0;
  60.         for (int mid = 0;; ++mid) {
  61.             if (mid != EOF_INDEX && exclusions.contains(mid)) {
  62.                 continue;
  63.             }
  64.             sum += _count[mid];
  65.             if (sum > midCount) {
  66.                 return (mid == EOF_INDEX) ? ArithCodeModel.EOF : mid;
  67.             }
  68.         }
  69.     }
  70.  
  71.     /**
  72.      * Total count for interval given specified set of exclusions.
  73.      *
  74.      * @param exclusions Bytes to exclude as outcomes.
  75.      * @return Total count of all non-excluded outcomes.
  76.      */
  77.     public int totalCount(ByteSet exclusions) {
  78.         int total = 0;
  79.         for (int i = 0; i < _count.length; ++i) {
  80.             if (i == EOF_INDEX || !exclusions.contains(i)) {
  81.                 total += _count[i];
  82.             }
  83.         }
  84.         return total;
  85.     }
  86.  
  87.     /**
  88.      * Increment the count for the given outcome.
  89.      *
  90.      * @param i Outcome to increment
  91.      */
  92.     public void increment(int i) {
  93.         if (++_count[i] > MAX_INDIVIDUAL_COUNT) {
  94.             rescale();
  95.         }
  96.     }
  97.     /**
  98.      * Counts for each outcome. Indices 0 to 255 for the usual counts, 256 for
  99.      * end-of-file, and 257 for total.
  100.      */
  101.     private int[] _count;
  102.  
  103.     /**
  104.      * Rescale the counts by dividing all frequencies by 2, but taking a minimum
  105.      * of 1.
  106.      */
  107.     private void rescale() {
  108.         for (int i = 0; i < _count.length; ++i) {
  109.             _count[i] = (_count[i] + 1) / 2;
  110.         }
  111.     }
  112.     /**
  113.      * Maximum count before rescaling.
  114.      */
  115.     private static final int MAX_INDIVIDUAL_COUNT = 8 * 1024;
  116.     /**
  117.      * Index in the count array for the end-of-file outcome.
  118.      */
  119.     private static final int EOF_INDEX = 256;
  120. }

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