gcc/libjava/classpath/java/util/zip/InflaterHuffmanTree.java

/* InflaterHuffmanTree.java --
   Copyright (C) 2001, 2004  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package java.util.zip;

class InflaterHuffmanTree
{
  private static final int MAX_BITLEN = 15;

  private short[] tree;

  static InflaterHuffmanTree defLitLenTree, defDistTree;

  static
  {
    try
      {
        byte[] codeLengths = new byte[288];
        int i = 0;
        while (i < 144)
          codeLengths[i++] = 8;
        while (i < 256)
          codeLengths[i++] = 9;
        while (i < 280)
          codeLengths[i++] = 7;
        while (i < 288)
          codeLengths[i++] = 8;
        defLitLenTree = new InflaterHuffmanTree(codeLengths);

        codeLengths = new byte[32];
        i = 0;
        while (i < 32)
          codeLengths[i++] = 5;
        defDistTree = new InflaterHuffmanTree(codeLengths);
      }
    catch (DataFormatException ex)
      {
        throw new InternalError
          ("InflaterHuffmanTree: static tree length illegal");
      }
  }

  /**
   * Constructs a Huffman tree from the array of code lengths.
   *
   * @param codeLengths the array of code lengths
   */
  InflaterHuffmanTree(byte[] codeLengths) throws DataFormatException
  {
    buildTree(codeLengths);
  }

  private void buildTree(byte[] codeLengths) throws DataFormatException
  {
    int[] blCount = new int[MAX_BITLEN+1];
    int[] nextCode = new int[MAX_BITLEN+1];
    for (int i = 0; i < codeLengths.length; i++)
      {
        int bits = codeLengths[i];
        if (bits > 0)
          blCount[bits]++;
      }

    int max = 0;
    int code = 0;
    int treeSize = 512;
    for (int bits = 1; bits <= MAX_BITLEN; bits++)
      {
        nextCode[bits] = code;
        if (blCount[bits] > 0)
          max = bits;
        code += blCount[bits] << (16 - bits);
        if (bits >= 10)
          {
            /* We need an extra table for bit lengths >= 10. */
            int start = nextCode[bits] & 0x1ff80;
            int end   = code & 0x1ff80;
            treeSize += (end - start) >> (16 - bits);
          }
      }
    if (code != 65536 && max > 1)
      throw new DataFormatException("incomplete dynamic bit lengths tree");

    /* Now create and fill the extra tables from longest to shortest
     * bit len.  This way the sub trees will be aligned.
     */
    tree = new short[treeSize];
    int treePtr = 512;
    for (int bits = MAX_BITLEN; bits >= 10; bits--)
      {
        int end   = code & 0x1ff80;
        code -= blCount[bits] << (16 - bits);
        int start = code & 0x1ff80;
        for (int i = start; i < end; i += 1 << 7)
          {
            tree[DeflaterHuffman.bitReverse(i)]
              = (short) ((-treePtr << 4) | bits);
            treePtr += 1 << (bits-9);
          }
      }

    for (int i = 0; i < codeLengths.length; i++)
      {
        int bits = codeLengths[i];
        if (bits == 0)
          continue;
        code = nextCode[bits];
        int revcode = DeflaterHuffman.bitReverse(code);
        if (bits <= 9)
          {
            do
              {
                tree[revcode] = (short) ((i << 4) | bits);
                revcode += 1 << bits;
              }
            while (revcode < 512);
          }
        else
          {
            int subTree = tree[revcode & 511];
            int treeLen = 1 << (subTree & 15);
            subTree = -(subTree >> 4);
            do
              {
                tree[subTree | (revcode >> 9)] = (short) ((i << 4) | bits);
                revcode += 1 << bits;
              }
            while (revcode < treeLen);
          }
        nextCode[bits] = code + (1 << (16 - bits));
      }
  }

  /**
   * Reads the next symbol from input.  The symbol is encoded using the
   * huffman tree.
   * @param input the input source.
   * @return the next symbol, or -1 if not enough input is available.
   */
  int getSymbol(StreamManipulator input) throws DataFormatException
  {
    int lookahead, symbol;
    if ((lookahead = input.peekBits(9)) >= 0)
      {
        if ((symbol = tree[lookahead]) >= 0)
          {
            input.dropBits(symbol & 15);
            return symbol >> 4;
          }
        int subtree = -(symbol >> 4);
        int bitlen = symbol & 15;
        if ((lookahead = input.peekBits(bitlen)) >= 0)
          {
            symbol = tree[subtree | (lookahead >> 9)];
            input.dropBits(symbol & 15);
            return symbol >> 4;
          }
        else
          {
            int bits = input.getAvailableBits();
            lookahead = input.peekBits(bits);
            symbol = tree[subtree | (lookahead >> 9)];
            if ((symbol & 15) <= bits)
              {
                input.dropBits(symbol & 15);
                return symbol >> 4;
              }
            else
              return -1;
          }
      }
    else
      {
        int bits = input.getAvailableBits();
        lookahead = input.peekBits(bits);
        symbol = tree[lookahead];
        if (symbol >= 0 && (symbol & 15) <= bits)
          {
            input.dropBits(symbol & 15);
            return symbol >> 4;
          }
        else
          return -1;
      }
  }
}