Tree.java

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

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/*
 * This program is based on zlib-1.1.3, so all credit should go authors
 * Jean-loup Gailly([email protected]) and Mark Adler([email protected])
 * 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, s.next_code);
  }

  // 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.
  private final 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){
    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.
    next_code[0]=0;
    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
  private final 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;
  }
}