xref: /illumos-gate/usr/src/common/bzip2/huffman.c (revision b9071c34)
1 
2 /*-------------------------------------------------------------*/
3 /*--- Huffman coding low-level stuff                        ---*/
4 /*---                                             huffman.c ---*/
5 /*-------------------------------------------------------------*/
6 
7 /* ------------------------------------------------------------------
8    This file is part of bzip2/libbzip2, a program and library for
9    lossless, block-sorting data compression.
10 
11    bzip2/libbzip2 version 1.0.6 of 6 September 2010
12    Copyright (C) 1996-2010 Julian Seward <jseward@bzip.org>
13 
14    Please read the WARNING, DISCLAIMER and PATENTS sections in the
15    README file.
16 
17    This program is released under the terms of the license contained
18    in the file LICENSE.
19    ------------------------------------------------------------------ */
20 
21 
22 #include "bzlib_private.h"
23 
24 /*---------------------------------------------------*/
25 #define WEIGHTOF(zz0)  ((zz0) & 0xffffff00)
26 #define DEPTHOF(zz1)   ((zz1) & 0x000000ff)
27 #define MYMAX(zz2,zz3) ((zz2) > (zz3) ? (zz2) : (zz3))
28 
29 #define ADDWEIGHTS(zw1,zw2)                           \
30    (WEIGHTOF(zw1)+WEIGHTOF(zw2)) |                    \
31    (1 + MYMAX(DEPTHOF(zw1),DEPTHOF(zw2)))
32 
33 #define UPHEAP(z)                                     \
34 {                                                     \
35    Int32 zz, tmp;                                     \
36    zz = z; tmp = heap[zz];                            \
37    while (weight[tmp] < weight[heap[zz >> 1]]) {      \
38       heap[zz] = heap[zz >> 1];                       \
39       zz >>= 1;                                       \
40    }                                                  \
41    heap[zz] = tmp;                                    \
42 }
43 
44 #define DOWNHEAP(z)                                   \
45 {                                                     \
46    Int32 zz, yy, tmp;                                 \
47    zz = z; tmp = heap[zz];                            \
48    while (True) {                                     \
49       yy = zz << 1;                                   \
50       if (yy > nHeap) break;                          \
51       if (yy < nHeap &&                               \
52           weight[heap[yy+1]] < weight[heap[yy]])      \
53          yy++;                                        \
54       if (weight[tmp] < weight[heap[yy]]) break;      \
55       heap[zz] = heap[yy];                            \
56       zz = yy;                                        \
57    }                                                  \
58    heap[zz] = tmp;                                    \
59 }
60 
61 
62 /*---------------------------------------------------*/
BZ2_hbMakeCodeLengths(UChar * len,Int32 * freq,Int32 alphaSize,Int32 maxLen)63 void BZ2_hbMakeCodeLengths ( UChar *len,
64                              Int32 *freq,
65                              Int32 alphaSize,
66                              Int32 maxLen )
67 {
68    /*--
69       Nodes and heap entries run from 1.  Entry 0
70       for both the heap and nodes is a sentinel.
71    --*/
72    Int32 nNodes, nHeap, n1, n2, i, j, k;
73    Bool  tooLong;
74 
75    Int32 heap   [ BZ_MAX_ALPHA_SIZE + 2 ];
76    Int32 weight [ BZ_MAX_ALPHA_SIZE * 2 ];
77    Int32 parent [ BZ_MAX_ALPHA_SIZE * 2 ];
78 
79    for (i = 0; i < alphaSize; i++)
80       weight[i+1] = (freq[i] == 0 ? 1 : freq[i]) << 8;
81 
82    while (True) {
83 
84       nNodes = alphaSize;
85       nHeap = 0;
86 
87       heap[0] = 0;
88       weight[0] = 0;
89       parent[0] = -2;
90 
91       for (i = 1; i <= alphaSize; i++) {
92          parent[i] = -1;
93          nHeap++;
94          heap[nHeap] = i;
95          UPHEAP(nHeap);
96       }
97 
98       AssertH( nHeap < (BZ_MAX_ALPHA_SIZE+2), 2001 );
99 
100       while (nHeap > 1) {
101          n1 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
102          n2 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
103          nNodes++;
104          parent[n1] = parent[n2] = nNodes;
105          weight[nNodes] = ADDWEIGHTS(weight[n1], weight[n2]);
106          parent[nNodes] = -1;
107          nHeap++;
108          heap[nHeap] = nNodes;
109          UPHEAP(nHeap);
110       }
111 
112       AssertH( nNodes < (BZ_MAX_ALPHA_SIZE * 2), 2002 );
113 
114       tooLong = False;
115       for (i = 1; i <= alphaSize; i++) {
116          j = 0;
117          k = i;
118          while (parent[k] >= 0) { k = parent[k]; j++; }
119          len[i-1] = j;
120          if (j > maxLen) tooLong = True;
121       }
122 
123       if (! tooLong) break;
124 
125       /* 17 Oct 04: keep-going condition for the following loop used
126          to be 'i < alphaSize', which missed the last element,
127          theoretically leading to the possibility of the compressor
128          looping.  However, this count-scaling step is only needed if
129          one of the generated Huffman code words is longer than
130          maxLen, which up to and including version 1.0.2 was 20 bits,
131          which is extremely unlikely.  In version 1.0.3 maxLen was
132          changed to 17 bits, which has minimal effect on compression
133          ratio, but does mean this scaling step is used from time to
134          time, enough to verify that it works.
135 
136          This means that bzip2-1.0.3 and later will only produce
137          Huffman codes with a maximum length of 17 bits.  However, in
138          order to preserve backwards compatibility with bitstreams
139          produced by versions pre-1.0.3, the decompressor must still
140          handle lengths of up to 20. */
141 
142       for (i = 1; i <= alphaSize; i++) {
143          j = weight[i] >> 8;
144          j = 1 + (j / 2);
145          weight[i] = j << 8;
146       }
147    }
148 }
149 
150 
151 /*---------------------------------------------------*/
BZ2_hbAssignCodes(Int32 * code,UChar * length,Int32 minLen,Int32 maxLen,Int32 alphaSize)152 void BZ2_hbAssignCodes ( Int32 *code,
153                          UChar *length,
154                          Int32 minLen,
155                          Int32 maxLen,
156                          Int32 alphaSize )
157 {
158    Int32 n, vec, i;
159 
160    vec = 0;
161    for (n = minLen; n <= maxLen; n++) {
162       for (i = 0; i < alphaSize; i++)
163          if (length[i] == n) { code[i] = vec; vec++; };
164       vec <<= 1;
165    }
166 }
167 
168 
169 /*---------------------------------------------------*/
BZ2_hbCreateDecodeTables(Int32 * limit,Int32 * base,Int32 * perm,UChar * length,Int32 minLen,Int32 maxLen,Int32 alphaSize)170 void BZ2_hbCreateDecodeTables ( Int32 *limit,
171                                 Int32 *base,
172                                 Int32 *perm,
173                                 UChar *length,
174                                 Int32 minLen,
175                                 Int32 maxLen,
176                                 Int32 alphaSize )
177 {
178    Int32 pp, i, j, vec;
179 
180    pp = 0;
181    for (i = minLen; i <= maxLen; i++)
182       for (j = 0; j < alphaSize; j++)
183          if (length[j] == i) { perm[pp] = j; pp++; };
184 
185    for (i = 0; i < BZ_MAX_CODE_LEN; i++) base[i] = 0;
186    for (i = 0; i < alphaSize; i++) base[length[i]+1]++;
187 
188    for (i = 1; i < BZ_MAX_CODE_LEN; i++) base[i] += base[i-1];
189 
190    for (i = 0; i < BZ_MAX_CODE_LEN; i++) limit[i] = 0;
191    vec = 0;
192 
193    for (i = minLen; i <= maxLen; i++) {
194       vec += (base[i+1] - base[i]);
195       limit[i] = vec-1;
196       vec <<= 1;
197    }
198    for (i = minLen + 1; i <= maxLen; i++)
199       base[i] = ((limit[i-1] + 1) << 1) - base[i];
200 }
201 
202 
203 /*-------------------------------------------------------------*/
204 /*--- end                                         huffman.c ---*/
205 /*-------------------------------------------------------------*/
206