kc3-lang/brotli/java/dec/Huffman.java

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• Hash : 5025365d
  Author :
  Date : 2016-10-17T14:04:59
  

  Add Java port of Brotli decoder.
  

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• java/dec/Huffman.java

• /* Copyright 2015 Google Inc. All Rights Reserved.
  
     Distributed under MIT license.
     See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
  */
  
  package org.brotli.dec;
  
  /**
   * Utilities for building Huffman decoding tables.
   */
  final class Huffman {
  
    /**
     * Maximum possible Huffman table size for an alphabet size of 704, max code length 15 and root
     * table bits 8.
     */
    static final int HUFFMAN_MAX_TABLE_SIZE = 1080;
  
    private static final int MAX_LENGTH = 15;
  
    /**
     * Returns reverse(reverse(key, len) + 1, len).
     *
     * <p> reverse(key, len) is the bit-wise reversal of the len least significant bits of key.
     */
    private static int getNextKey(int key, int len) {
      int step = 1 << (len - 1);
      while ((key & step) != 0) {
        step >>= 1;
      }
      return (key & (step - 1)) + step;
    }
  
    /**
     * Stores {@code item} in {@code table[0], table[step], table[2 * step] .., table[end]}.
     *
     * <p> Assumes that end is an integer multiple of step.
     */
    private static void replicateValue(int[] table, int offset, int step, int end, int item) {
      do {
        end -= step;
        table[offset + end] = item;
      } while (end > 0);
    }
  
    /**
     * @param count histogram of bit lengths for the remaining symbols,
     * @param len code length of the next processed symbol.
     * @return table width of the next 2nd level table.
     */
    private static int nextTableBitSize(int[] count, int len, int rootBits) {
      int left = 1 << (len - rootBits);
      while (len < MAX_LENGTH) {
        left -= count[len];
        if (left <= 0) {
          break;
        }
        len++;
        left <<= 1;
      }
      return len - rootBits;
    }
  
    /**
     * Builds Huffman lookup table assuming code lengths are in symbol order.
     */
    static void buildHuffmanTable(int[] rootTable, int tableOffset, int rootBits, int[] codeLengths,
        int codeLengthsSize) {
      int key; // Reversed prefix code.
      int[] sorted = new int[codeLengthsSize]; // Symbols sorted by code length.
      // TODO: fill with zeroes?
      int[] count = new int[MAX_LENGTH + 1]; // Number of codes of each length.
      int[] offset = new int[MAX_LENGTH + 1]; // Offsets in sorted table for each length.
      int symbol;
  
      // Build histogram of code lengths.
      for (symbol = 0; symbol < codeLengthsSize; symbol++) {
        count[codeLengths[symbol]]++;
      }
  
      // Generate offsets into sorted symbol table by code length.
      offset[1] = 0;
      for (int len = 1; len < MAX_LENGTH; len++) {
        offset[len + 1] = offset[len] + count[len];
      }
  
      // Sort symbols by length, by symbol order within each length.
      for (symbol = 0; symbol < codeLengthsSize; symbol++) {
        if (codeLengths[symbol] != 0) {
          sorted[offset[codeLengths[symbol]]++] = symbol;
        }
      }
  
      int tableBits = rootBits;
      int tableSize = 1 << tableBits;
      int totalSize = tableSize;
  
      // Special case code with only one value.
      if (offset[MAX_LENGTH] == 1) {
        for (key = 0; key < totalSize; key++) {
          rootTable[tableOffset + key] = sorted[0];
        }
        return;
      }
  
      // Fill in root table.
      key = 0;
      symbol = 0;
      for (int len = 1, step = 2; len <= rootBits; len++, step <<= 1) {
        for (; count[len] > 0; count[len]--) {
          replicateValue(rootTable, tableOffset + key, step, tableSize, len << 16 | sorted[symbol++]);
          key = getNextKey(key, len);
        }
      }
  
      // Fill in 2nd level tables and add pointers to root table.
      int mask = totalSize - 1;
      int low = -1;
      int currentOffset = tableOffset;
      for (int len = rootBits + 1, step = 2; len <= MAX_LENGTH; len++, step <<= 1) {
        for (; count[len] > 0; count[len]--) {
          if ((key & mask) != low) {
            currentOffset += tableSize;
            tableBits = nextTableBitSize(count, len, rootBits);
            tableSize = 1 << tableBits;
            totalSize += tableSize;
            low = key & mask;
            rootTable[tableOffset + low] =
                (tableBits + rootBits) << 16 | (currentOffset - tableOffset - low);
          }
          replicateValue(rootTable, currentOffset + (key >> rootBits), step, tableSize,
              (len - rootBits) << 16 | sorted[symbol++]);
          key = getNextKey(key, len);
        }
      }
    }
  }
  

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