k-9/src/com/jcraft/jzlib/Tree.java

/* -*-mode:java; c-basic-offset:2; -*- */
/*
Copyright (c) 2000,2001,2002,2003 ymnk, JCraft,Inc. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice,
     this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright 
     notice, this list of conditions and the following disclaimer in 
     the documentation and/or other materials provided with the distribution.

  3. The names of the authors may not be used to endorse or promote products
     derived from this software without specific prior written permission.

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/*
 * This program is based on zlib-1.1.3, so all credit should go authors
 * Jean-loup Gailly(jloup@gzip.org) and Mark Adler(madler@alumni.caltech.edu)
 * and contributors of zlib.
 */

package com.jcraft.jzlib;

final class Tree{
  static final private int MAX_BITS=15;
  static final private int BL_CODES=19;
  static final private int D_CODES=30;
  static final private int LITERALS=256;
  static final private int LENGTH_CODES=29;
  static final private int L_CODES=(LITERALS+1+LENGTH_CODES);
  static final private int HEAP_SIZE=(2*L_CODES+1);

  // Bit length codes must not exceed MAX_BL_BITS bits
  static final int MAX_BL_BITS=7; 

  // end of block literal code
  static final int END_BLOCK=256; 

  // repeat previous bit length 3-6 times (2 bits of repeat count)
  static final int REP_3_6=16; 

  // repeat a zero length 3-10 times  (3 bits of repeat count)
  static final int REPZ_3_10=17; 

  // repeat a zero length 11-138 times  (7 bits of repeat count)
  static final int REPZ_11_138=18; 

  // extra bits for each length code
  static final int[] extra_lbits={
    0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0
  };

  // extra bits for each distance code
  static final int[] extra_dbits={
    0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13
  };

  // extra bits for each bit length code
  static final int[] extra_blbits={
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7
  };

  static final byte[] bl_order={
    16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};


  // The lengths of the bit length codes are sent in order of decreasing
  // probability, to avoid transmitting the lengths for unused bit
  // length codes.

  static final int Buf_size=8*2;

  // see definition of array dist_code below
  static final int DIST_CODE_LEN=512;

  static final byte[] _dist_code = {
    0,  1,  2,  3,  4,  4,  5,  5,  6,  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  8,
    8,  8,  8,  8,  9,  9,  9,  9,  9,  9,  9,  9, 10, 10, 10, 10, 10, 10, 10, 10,
    10, 10, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
    11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
    12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13,
    13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
    13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
    14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
    14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
    14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 15,
    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,  0,  0, 16, 17,
    18, 18, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22, 22, 22,
    23, 23, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
    24, 24, 24, 24, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
    26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
    26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27,
    27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
    27, 27, 27, 27, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
    28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
    28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
    28, 28, 28, 28, 28, 28, 28, 28, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
    29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
    29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
    29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29
  };

  static final byte[] _length_code={
    0,  1,  2,  3,  4,  5,  6,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 12, 12,
    13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
    17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
    19, 19, 19, 19, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
    21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
    22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
    23, 23, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
    24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
    25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
    25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
    26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
    26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
    27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 28
  };

  static final int[] base_length = {
    0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
    64, 80, 96, 112, 128, 160, 192, 224, 0
  };

  static final int[] base_dist = {
       0,   1,      2,     3,     4,    6,     8,    12,    16,     24,
      32,  48,     64,    96,   128,  192,   256,   384,   512,    768,
    1024, 1536,  2048,  3072,  4096,  6144,  8192, 12288, 16384, 24576
  };

  // Mapping from a distance to a distance code. dist is the distance - 1 and
  // must not have side effects. _dist_code[256] and _dist_code[257] are never
  // used.
  static int d_code(int dist){
    return ((dist) < 256 ? _dist_code[dist] : _dist_code[256+((dist)>>>7)]);
  }

  short[] dyn_tree;      // the dynamic tree
  int     max_code;      // largest code with non zero frequency
  StaticTree stat_desc;  // the corresponding static tree

  // Compute the optimal bit lengths for a tree and update the total bit length
  // for the current block.
  // IN assertion: the fields freq and dad are set, heap[heap_max] and
  //    above are the tree nodes sorted by increasing frequency.
  // OUT assertions: the field len is set to the optimal bit length, the
  //     array bl_count contains the frequencies for each bit length.
  //     The length opt_len is updated; static_len is also updated if stree is
  //     not null.
  void gen_bitlen(Deflate s){
    short[] tree = dyn_tree;
    short[] stree = stat_desc.static_tree;
    int[] extra = stat_desc.extra_bits;
    int base = stat_desc.extra_base;
    int max_length = stat_desc.max_length;
    int h;              // heap index
    int n, m;           // iterate over the tree elements
    int bits;           // bit length
    int xbits;          // extra bits
    short f;            // frequency
    int overflow = 0;   // number of elements with bit length too large

    for (bits = 0; bits <= MAX_BITS; bits++) s.bl_count[bits] = 0;

    // In a first pass, compute the optimal bit lengths (which may
    // overflow in the case of the bit length tree).
    tree[s.heap[s.heap_max]*2+1] = 0; // root of the heap

    for(h=s.heap_max+1; h<HEAP_SIZE; h++){
      n = s.heap[h];
      bits = tree[tree[n*2+1]*2+1] + 1;
      if (bits > max_length){ bits = max_length; overflow++; }
      tree[n*2+1] = (short)bits;
      // We overwrite tree[n*2+1] which is no longer needed

      if (n > max_code) continue;  // not a leaf node

      s.bl_count[bits]++;
      xbits = 0;
      if (n >= base) xbits = extra[n-base];
      f = tree[n*2];
      s.opt_len += f * (bits + xbits);
      if (stree!=null) s.static_len += f * (stree[n*2+1] + xbits);
    }
    if (overflow == 0) return;

    // This happens for example on obj2 and pic of the Calgary corpus
    // Find the first bit length which could increase:
    do {
      bits = max_length-1;
      while(s.bl_count[bits]==0) bits--;
      s.bl_count[bits]--;      // move one leaf down the tree
      s.bl_count[bits+1]+=2;   // move one overflow item as its brother
      s.bl_count[max_length]--;
      // The brother of the overflow item also moves one step up,
      // but this does not affect bl_count[max_length]
      overflow -= 2;
    }
    while (overflow > 0);

    for (bits = max_length; bits != 0; bits--) {
      n = s.bl_count[bits];
      while (n != 0) {
	m = s.heap[--h];
	if (m > max_code) continue;
	if (tree[m*2+1] != bits) {
	  s.opt_len += ((long)bits - (long)tree[m*2+1])*(long)tree[m*2];
	  tree[m*2+1] = (short)bits;
	}
	n--;
      }
    }
  }

  // Construct one Huffman tree and assigns the code bit strings and lengths.
  // Update the total bit length for the current block.
  // IN assertion: the field freq is set for all tree elements.
  // OUT assertions: the fields len and code are set to the optimal bit length
  //     and corresponding code. The length opt_len is updated; static_len is
  //     also updated if stree is not null. The field max_code is set.
  void build_tree(Deflate s){
    short[] tree=dyn_tree;
    short[] stree=stat_desc.static_tree;
    int elems=stat_desc.elems;
    int n, m;          // iterate over heap elements
    int max_code=-1;   // largest code with non zero frequency
    int node;          // new node being created

    // Construct the initial heap, with least frequent element in
    // heap[1]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
    // heap[0] is not used.
    s.heap_len = 0;
    s.heap_max = HEAP_SIZE;

    for(n=0; n<elems; n++) {
      if(tree[n*2] != 0) {
	s.heap[++s.heap_len] = max_code = n;
	s.depth[n] = 0;
      }
      else{
	tree[n*2+1] = 0;
      }
    }

    // The pkzip format requires that at least one distance code exists,
    // and that at least one bit should be sent even if there is only one
    // possible code. So to avoid special checks later on we force at least
    // two codes of non zero frequency.
    while (s.heap_len < 2) {
      node = s.heap[++s.heap_len] = (max_code < 2 ? ++max_code : 0);
      tree[node*2] = 1;
      s.depth[node] = 0;
      s.opt_len--; if (stree!=null) s.static_len -= stree[node*2+1];
      // node is 0 or 1 so it does not have extra bits
    }
    this.max_code = max_code;

    // The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
    // establish sub-heaps of increasing lengths:

    for(n=s.heap_len/2;n>=1; n--)
      s.pqdownheap(tree, n);

    // Construct the Huffman tree by repeatedly combining the least two
    // frequent nodes.

    node=elems;                 // next internal node of the tree
    do{
      // n = node of least frequency
      n=s.heap[1];
      s.heap[1]=s.heap[s.heap_len--];
      s.pqdownheap(tree, 1);
      m=s.heap[1];                // m = node of next least frequency

      s.heap[--s.heap_max] = n; // keep the nodes sorted by frequency
      s.heap[--s.heap_max] = m;

      // Create a new node father of n and m
      tree[node*2] = (short)(tree[n*2] + tree[m*2]);
      s.depth[node] = (byte)(Math.max(s.depth[n],s.depth[m])+1);
      tree[n*2+1] = tree[m*2+1] = (short)node;

      // and insert the new node in the heap
      s.heap[1] = node++;
      s.pqdownheap(tree, 1);
    }
    while(s.heap_len>=2);

    s.heap[--s.heap_max] = s.heap[1];

    // At this point, the fields freq and dad are set. We can now
    // generate the bit lengths.

    gen_bitlen(s);

    // The field len is now set, we can generate the bit codes
    gen_codes(tree, max_code, s.bl_count);
  }

  // Generate the codes for a given tree and bit counts (which need not be
  // optimal).
  // IN assertion: the array bl_count contains the bit length statistics for
  // the given tree and the field len is set for all tree elements.
  // OUT assertion: the field code is set for all tree elements of non
  //     zero code length.
  static void gen_codes(short[] tree, // the tree to decorate
			int max_code, // largest code with non zero frequency
			short[] bl_count // number of codes at each bit length
			){
    short[] next_code=new short[MAX_BITS+1]; // next code value for each bit length
    short code = 0;            // running code value
    int bits;                  // bit index
    int n;                     // code index

    // The distribution counts are first used to generate the code values
    // without bit reversal.
    for (bits = 1; bits <= MAX_BITS; bits++) {
      next_code[bits] = code = (short)((code + bl_count[bits-1]) << 1);
    }

    // Check that the bit counts in bl_count are consistent. The last code
    // must be all ones.
    //Assert (code + bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1,
    //        "inconsistent bit counts");
    //Tracev((stderr,"\ngen_codes: max_code %d ", max_code));

    for (n = 0;  n <= max_code; n++) {
      int len = tree[n*2+1];
      if (len == 0) continue;
      // Now reverse the bits
      tree[n*2] = (short)(bi_reverse(next_code[len]++, len));
    }
  }

  // Reverse the first len bits of a code, using straightforward code (a faster
  // method would use a table)
  // IN assertion: 1 <= len <= 15
  static int bi_reverse(int code, // the value to invert
			int len   // its bit length
			){
    int res = 0;
    do{
      res|=code&1;
      code>>>=1;
      res<<=1;
    } 
    while(--len>0);
    return res>>>1;
  }
}