Tree


1   /* -*-mode:java; c-basic-offset:2; -*- */
2   /*
3   Copyright (c) 2000,2001,2002,2003 ymnk, JCraft,Inc. All rights reserved.
4   
5   Redistribution and use in source and binary forms, with or without
6   modification, are permitted provided that the following conditions are met:
7   
8     1. Redistributions of source code must retain the above copyright notice,
9        this list of conditions and the following disclaimer.
10  
11    2. Redistributions in binary form must reproduce the above copyright 
12       notice, this list of conditions and the following disclaimer in 
13       the documentation and/or other materials provided with the distribution.
14  
15    3. The names of the authors may not be used to endorse or promote products
16       derived from this software without specific prior written permission.
17  
18  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
19  INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
20  FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL JCRAFT,
21  INC. OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY DIRECT, INDIRECT,
22  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
23  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
24  OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
25  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
26  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
27  EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28   */
29  /*
30   * This program is based on zlib-1.1.3, so all credit should go authors
31   * Jean-loup Gailly(jloup@gzip.org) and Mark Adler(madler@alumni.caltech.edu)
32   * and contributors of zlib.
33   */
34  
35  package com.jcraft.jzlib;
36  
37  final class Tree{
38    static final private int MAX_BITS=15;
39    static final private int BL_CODES=19;
40    static final private int D_CODES=30;
41    static final private int LITERALS=256;
42    static final private int LENGTH_CODES=29;
43    static final private int L_CODES=(LITERALS+1+LENGTH_CODES);
44    static final private int HEAP_SIZE=(2*L_CODES+1);
45  
46    // Bit length codes must not exceed MAX_BL_BITS bits
47    static final int MAX_BL_BITS=7; 
48  
49    // end of block literal code
50    static final int END_BLOCK=256; 
51  
52    // repeat previous bit length 3-6 times (2 bits of repeat count)
53    static final int REP_3_6=16; 
54  
55    // repeat a zero length 3-10 times  (3 bits of repeat count)
56    static final int REPZ_3_10=17; 
57  
58    // repeat a zero length 11-138 times  (7 bits of repeat count)
59    static final int REPZ_11_138=18; 
60  
61    // extra bits for each length code
62    static final int[] extra_lbits={
63      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
64    };
65  
66    // extra bits for each distance code
67    static final int[] extra_dbits={
68      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
69    };
70  
71    // extra bits for each bit length code
72    static final int[] extra_blbits={
73      0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7
74    };
75  
76    static final byte[] bl_order={
77      16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};
78  
79  
80    // The lengths of the bit length codes are sent in order of decreasing
81    // probability, to avoid transmitting the lengths for unused bit
82    // length codes.
83  
84    static final int Buf_size=8*2;
85  
86    // see definition of array dist_code below
87    static final int DIST_CODE_LEN=512;
88  
89    static final byte[] _dist_code = {
90      0,  1,  2,  3,  4,  4,  5,  5,  6,  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  8,
91      8,  8,  8,  8,  9,  9,  9,  9,  9,  9,  9,  9, 10, 10, 10, 10, 10, 10, 10, 10,
92      10, 10, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
93      11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
94      12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13,
95      13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
96      13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
97      14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
98      14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
99      14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 15,
100     15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
101     15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
102     15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,  0,  0, 16, 17,
103     18, 18, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22, 22, 22,
104     23, 23, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
105     24, 24, 24, 24, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
106     26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
107     26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27,
108     27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
109     27, 27, 27, 27, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
110     28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
111     28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
112     28, 28, 28, 28, 28, 28, 28, 28, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
113     29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
114     29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
115     29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29
116   };
117 
118   static final byte[] _length_code={
119     0,  1,  2,  3,  4,  5,  6,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 12, 12,
120     13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
121     17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
122     19, 19, 19, 19, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
123     21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
124     22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
125     23, 23, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
126     24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
127     25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
128     25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
129     26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
130     26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
131     27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 28
132   };
133 
134   static final int[] base_length = {
135     0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
136     64, 80, 96, 112, 128, 160, 192, 224, 0
137   };
138 
139   static final int[] base_dist = {
140        0,   1,      2,     3,     4,    6,     8,    12,    16,     24,
141       32,  48,     64,    96,   128,  192,   256,   384,   512,    768,
142     1024, 1536,  2048,  3072,  4096,  6144,  8192, 12288, 16384, 24576
143   };
144 
145   // Mapping from a distance to a distance code. dist is the distance - 1 and
146   // must not have side effects. _dist_code[256] and _dist_code[257] are never
147   // used.
148   static int d_code(int dist){
149     return ((dist) < 256 ? _dist_code[dist] : _dist_code[256+((dist)>>>7)]);
150   }
151 
152   short[] dyn_tree;      // the dynamic tree
153   int     max_code;      // largest code with non zero frequency
154   StaticTree stat_desc;  // the corresponding static tree
155 
156   // Compute the optimal bit lengths for a tree and update the total bit length
157   // for the current block.
158   // IN assertion: the fields freq and dad are set, heap[heap_max] and
159   //    above are the tree nodes sorted by increasing frequency.
160   // OUT assertions: the field len is set to the optimal bit length, the
161   //     array bl_count contains the frequencies for each bit length.
162   //     The length opt_len is updated; static_len is also updated if stree is
163   //     not null.
164   void gen_bitlen(Deflate s){
165     short[] tree = dyn_tree;
166     short[] stree = stat_desc.static_tree;
167     int[] extra = stat_desc.extra_bits;
168     int base = stat_desc.extra_base;
169     int max_length = stat_desc.max_length;
170     int h;              // heap index
171     int n, m;           // iterate over the tree elements
172     int bits;           // bit length
173     int xbits;          // extra bits
174     short f;            // frequency
175     int overflow = 0;   // number of elements with bit length too large
176 
177     for (bits = 0; bits <= MAX_BITS; bits++) s.bl_count[bits] = 0;
178 
179     // In a first pass, compute the optimal bit lengths (which may
180     // overflow in the case of the bit length tree).
181     tree[s.heap[s.heap_max]*2+1] = 0; // root of the heap
182 
183     for(h=s.heap_max+1; h<HEAP_SIZE; h++){
184       n = s.heap[h];
185       bits = tree[tree[n*2+1]*2+1] + 1;
186       if (bits > max_length){ bits = max_length; overflow++; }
187       tree[n*2+1] = (short)bits;
188       // We overwrite tree[n*2+1] which is no longer needed
189 
190       if (n > max_code) continue;  // not a leaf node
191 
192       s.bl_count[bits]++;
193       xbits = 0;
194       if (n >= base) xbits = extra[n-base];
195       f = tree[n*2];
196       s.opt_len += f * (bits + xbits);
197       if (stree!=null) s.static_len += f * (stree[n*2+1] + xbits);
198     }
199     if (overflow == 0) return;
200 
201     // This happens for example on obj2 and pic of the Calgary corpus
202     // Find the first bit length which could increase:
203     do {
204       bits = max_length-1;
205       while(s.bl_count[bits]==0) bits--;
206       s.bl_count[bits]--;      // move one leaf down the tree
207       s.bl_count[bits+1]+=2;   // move one overflow item as its brother
208       s.bl_count[max_length]--;
209       // The brother of the overflow item also moves one step up,
210       // but this does not affect bl_count[max_length]
211       overflow -= 2;
212     }
213     while (overflow > 0);
214 
215     for (bits = max_length; bits != 0; bits--) {
216       n = s.bl_count[bits];
217       while (n != 0) {
218     m = s.heap[--h];
219     if (m > max_code) continue;
220     if (tree[m*2+1] != bits) {
221       s.opt_len += ((long)bits - (long)tree[m*2+1])*(long)tree[m*2];
222       tree[m*2+1] = (short)bits;
223     }
224     n--;
225       }
226     }
227   }
228 
229   // Construct one Huffman tree and assigns the code bit strings and lengths.
230   // Update the total bit length for the current block.
231   // IN assertion: the field freq is set for all tree elements.
232   // OUT assertions: the fields len and code are set to the optimal bit length
233   //     and corresponding code. The length opt_len is updated; static_len is
234   //     also updated if stree is not null. The field max_code is set.
235   void build_tree(Deflate s){
236     short[] tree=dyn_tree;
237     short[] stree=stat_desc.static_tree;
238     int elems=stat_desc.elems;
239     int n, m;          // iterate over heap elements
240     int max_code=-1;   // largest code with non zero frequency
241     int node;          // new node being created
242 
243     // Construct the initial heap, with least frequent element in
244     // heap[1]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
245     // heap[0] is not used.
246     s.heap_len = 0;
247     s.heap_max = HEAP_SIZE;
248 
249     for(n=0; n<elems; n++) {
250       if(tree[n*2] != 0) {
251     s.heap[++s.heap_len] = max_code = n;
252     s.depth[n] = 0;
253       }
254       else{
255     tree[n*2+1] = 0;
256       }
257     }
258 
259     // The pkzip format requires that at least one distance code exists,
260     // and that at least one bit should be sent even if there is only one
261     // possible code. So to avoid special checks later on we force at least
262     // two codes of non zero frequency.
263     while (s.heap_len < 2) {
264       node = s.heap[++s.heap_len] = (max_code < 2 ? ++max_code : 0);
265       tree[node*2] = 1;
266       s.depth[node] = 0;
267       s.opt_len--; if (stree!=null) s.static_len -= stree[node*2+1];
268       // node is 0 or 1 so it does not have extra bits
269     }
270     this.max_code = max_code;
271 
272     // The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
273     // establish sub-heaps of increasing lengths:
274 
275     for(n=s.heap_len/2;n>=1; n--)
276       s.pqdownheap(tree, n);
277 
278     // Construct the Huffman tree by repeatedly combining the least two
279     // frequent nodes.
280 
281     node=elems;                 // next internal node of the tree
282     do{
283       // n = node of least frequency
284       n=s.heap[1];
285       s.heap[1]=s.heap[s.heap_len--];
286       s.pqdownheap(tree, 1);
287       m=s.heap[1];                // m = node of next least frequency
288 
289       s.heap[--s.heap_max] = n; // keep the nodes sorted by frequency
290       s.heap[--s.heap_max] = m;
291 
292       // Create a new node father of n and m
293       tree[node*2] = (short)(tree[n*2] + tree[m*2]);
294       s.depth[node] = (byte)(Math.max(s.depth[n],s.depth[m])+1);
295       tree[n*2+1] = tree[m*2+1] = (short)node;
296 
297       // and insert the new node in the heap
298       s.heap[1] = node++;
299       s.pqdownheap(tree, 1);
300     }
301     while(s.heap_len>=2);
302 
303     s.heap[--s.heap_max] = s.heap[1];
304 
305     // At this point, the fields freq and dad are set. We can now
306     // generate the bit lengths.
307 
308     gen_bitlen(s);
309 
310     // The field len is now set, we can generate the bit codes
311     gen_codes(tree, max_code, s.bl_count);
312   }
313 
314   // Generate the codes for a given tree and bit counts (which need not be
315   // optimal).
316   // IN assertion: the array bl_count contains the bit length statistics for
317   // the given tree and the field len is set for all tree elements.
318   // OUT assertion: the field code is set for all tree elements of non
319   //     zero code length.
320   static void gen_codes(short[] tree, // the tree to decorate
321             int max_code, // largest code with non zero frequency
322             short[] bl_count // number of codes at each bit length
323             ){
324     short[] next_code=new short[MAX_BITS+1]; // next code value for each bit length
325     short code = 0;            // running code value
326     int bits;                  // bit index
327     int n;                     // code index
328 
329     // The distribution counts are first used to generate the code values
330     // without bit reversal.
331     for (bits = 1; bits <= MAX_BITS; bits++) {
332       next_code[bits] = code = (short)((code + bl_count[bits-1]) << 1);
333     }
334 
335     // Check that the bit counts in bl_count are consistent. The last code
336     // must be all ones.
337     //Assert (code + bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1,
338     //        "inconsistent bit counts");
339     //Tracev((stderr,"\ngen_codes: max_code %d ", max_code));
340 
341     for (n = 0;  n <= max_code; n++) {
342       int len = tree[n*2+1];
343       if (len == 0) continue;
344       // Now reverse the bits
345       tree[n*2] = (short)(bi_reverse(next_code[len]++, len));
346     }
347   }
348 
349   // Reverse the first len bits of a code, using straightforward code (a faster
350   // method would use a table)
351   // IN assertion: 1 <= len <= 15
352   static int bi_reverse(int code, // the value to invert
353             int len   // its bit length
354             ){
355     int res = 0;
356     do{
357       res|=code&1;
358       code>>>=1;
359       res<<=1;
360     } 
361     while(--len>0);
362     return res>>>1;
363   }
364 }
365 
366
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