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source: vbox/trunk/src/libs/zlib-1.2.1/inftrees.c@ 7692

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export libpng and zlib so Windows and OS/2 builds cleanly.

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1/* inftrees.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2003 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6#include "zutil.h"
7#include "inftrees.h"
8
9#define MAXBITS 15
10
11const char inflate_copyright[] =
12 " inflate 1.2.1 Copyright 1995-2003 Mark Adler ";
13/*
14 If you use the zlib library in a product, an acknowledgment is welcome
15 in the documentation of your product. If for some reason you cannot
16 include such an acknowledgment, I would appreciate that you keep this
17 copyright string in the executable of your product.
18 */
19
20/*
21 Build a set of tables to decode the provided canonical Huffman code.
22 The code lengths are lens[0..codes-1]. The result starts at *table,
23 whose indices are 0..2^bits-1. work is a writable array of at least
24 lens shorts, which is used as a work area. type is the type of code
25 to be generated, CODES, LENS, or DISTS. On return, zero is success,
26 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
27 on return points to the next available entry's address. bits is the
28 requested root table index bits, and on return it is the actual root
29 table index bits. It will differ if the request is greater than the
30 longest code or if it is less than the shortest code.
31 */
32int inflate_table(type, lens, codes, table, bits, work)
33codetype type;
34unsigned short FAR *lens;
35unsigned codes;
36code FAR * FAR *table;
37unsigned FAR *bits;
38unsigned short FAR *work;
39{
40 unsigned len; /* a code's length in bits */
41 unsigned sym; /* index of code symbols */
42 unsigned min, max; /* minimum and maximum code lengths */
43 unsigned root; /* number of index bits for root table */
44 unsigned curr; /* number of index bits for current table */
45 unsigned drop; /* code bits to drop for sub-table */
46 int left; /* number of prefix codes available */
47 unsigned used; /* code entries in table used */
48 unsigned huff; /* Huffman code */
49 unsigned incr; /* for incrementing code, index */
50 unsigned fill; /* index for replicating entries */
51 unsigned low; /* low bits for current root entry */
52 unsigned mask; /* mask for low root bits */
53 code this; /* table entry for duplication */
54 code FAR *next; /* next available space in table */
55 const unsigned short FAR *base; /* base value table to use */
56 const unsigned short FAR *extra; /* extra bits table to use */
57 int end; /* use base and extra for symbol > end */
58 unsigned short count[MAXBITS+1]; /* number of codes of each length */
59 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
60 static const unsigned short lbase[31] = { /* Length codes 257..285 base */
61 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
62 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
63 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
64 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
65 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 76, 66};
66 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
67 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
68 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
69 8193, 12289, 16385, 24577, 0, 0};
70 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
71 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
72 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
73 28, 28, 29, 29, 64, 64};
74
75 /*
76 Process a set of code lengths to create a canonical Huffman code. The
77 code lengths are lens[0..codes-1]. Each length corresponds to the
78 symbols 0..codes-1. The Huffman code is generated by first sorting the
79 symbols by length from short to long, and retaining the symbol order
80 for codes with equal lengths. Then the code starts with all zero bits
81 for the first code of the shortest length, and the codes are integer
82 increments for the same length, and zeros are appended as the length
83 increases. For the deflate format, these bits are stored backwards
84 from their more natural integer increment ordering, and so when the
85 decoding tables are built in the large loop below, the integer codes
86 are incremented backwards.
87
88 This routine assumes, but does not check, that all of the entries in
89 lens[] are in the range 0..MAXBITS. The caller must assure this.
90 1..MAXBITS is interpreted as that code length. zero means that that
91 symbol does not occur in this code.
92
93 The codes are sorted by computing a count of codes for each length,
94 creating from that a table of starting indices for each length in the
95 sorted table, and then entering the symbols in order in the sorted
96 table. The sorted table is work[], with that space being provided by
97 the caller.
98
99 The length counts are used for other purposes as well, i.e. finding
100 the minimum and maximum length codes, determining if there are any
101 codes at all, checking for a valid set of lengths, and looking ahead
102 at length counts to determine sub-table sizes when building the
103 decoding tables.
104 */
105
106 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
107 for (len = 0; len <= MAXBITS; len++)
108 count[len] = 0;
109 for (sym = 0; sym < codes; sym++)
110 count[lens[sym]]++;
111
112 /* bound code lengths, force root to be within code lengths */
113 root = *bits;
114 for (max = MAXBITS; max >= 1; max--)
115 if (count[max] != 0) break;
116 if (root > max) root = max;
117 if (max == 0) return -1; /* no codes! */
118 for (min = 1; min <= MAXBITS; min++)
119 if (count[min] != 0) break;
120 if (root < min) root = min;
121
122 /* check for an over-subscribed or incomplete set of lengths */
123 left = 1;
124 for (len = 1; len <= MAXBITS; len++) {
125 left <<= 1;
126 left -= count[len];
127 if (left < 0) return -1; /* over-subscribed */
128 }
129 if (left > 0 && (type == CODES || (codes - count[0] != 1)))
130 return -1; /* incomplete set */
131
132 /* generate offsets into symbol table for each length for sorting */
133 offs[1] = 0;
134 for (len = 1; len < MAXBITS; len++)
135 offs[len + 1] = offs[len] + count[len];
136
137 /* sort symbols by length, by symbol order within each length */
138 for (sym = 0; sym < codes; sym++)
139 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
140
141 /*
142 Create and fill in decoding tables. In this loop, the table being
143 filled is at next and has curr index bits. The code being used is huff
144 with length len. That code is converted to an index by dropping drop
145 bits off of the bottom. For codes where len is less than drop + curr,
146 those top drop + curr - len bits are incremented through all values to
147 fill the table with replicated entries.
148
149 root is the number of index bits for the root table. When len exceeds
150 root, sub-tables are created pointed to by the root entry with an index
151 of the low root bits of huff. This is saved in low to check for when a
152 new sub-table should be started. drop is zero when the root table is
153 being filled, and drop is root when sub-tables are being filled.
154
155 When a new sub-table is needed, it is necessary to look ahead in the
156 code lengths to determine what size sub-table is needed. The length
157 counts are used for this, and so count[] is decremented as codes are
158 entered in the tables.
159
160 used keeps track of how many table entries have been allocated from the
161 provided *table space. It is checked when a LENS table is being made
162 against the space in *table, ENOUGH, minus the maximum space needed by
163 the worst case distance code, MAXD. This should never happen, but the
164 sufficiency of ENOUGH has not been proven exhaustively, hence the check.
165 This assumes that when type == LENS, bits == 9.
166
167 sym increments through all symbols, and the loop terminates when
168 all codes of length max, i.e. all codes, have been processed. This
169 routine permits incomplete codes, so another loop after this one fills
170 in the rest of the decoding tables with invalid code markers.
171 */
172
173 /* set up for code type */
174 switch (type) {
175 case CODES:
176 base = extra = work; /* dummy value--not used */
177 end = 19;
178 break;
179 case LENS:
180 base = lbase;
181 base -= 257;
182 extra = lext;
183 extra -= 257;
184 end = 256;
185 break;
186 default: /* DISTS */
187 base = dbase;
188 extra = dext;
189 end = -1;
190 }
191
192 /* initialize state for loop */
193 huff = 0; /* starting code */
194 sym = 0; /* starting code symbol */
195 len = min; /* starting code length */
196 next = *table; /* current table to fill in */
197 curr = root; /* current table index bits */
198 drop = 0; /* current bits to drop from code for index */
199 low = (unsigned)(-1); /* trigger new sub-table when len > root */
200 used = 1U << root; /* use root table entries */
201 mask = used - 1; /* mask for comparing low */
202
203 /* check available table space */
204 if (type == LENS && used >= ENOUGH - MAXD)
205 return 1;
206
207 /* process all codes and make table entries */
208 for (;;) {
209 /* create table entry */
210 this.bits = (unsigned char)(len - drop);
211 if ((int)(work[sym]) < end) {
212 this.op = (unsigned char)0;
213 this.val = work[sym];
214 }
215 else if ((int)(work[sym]) > end) {
216 this.op = (unsigned char)(extra[work[sym]]);
217 this.val = base[work[sym]];
218 }
219 else {
220 this.op = (unsigned char)(32 + 64); /* end of block */
221 this.val = 0;
222 }
223
224 /* replicate for those indices with low len bits equal to huff */
225 incr = 1U << (len - drop);
226 fill = 1U << curr;
227 do {
228 fill -= incr;
229 next[(huff >> drop) + fill] = this;
230 } while (fill != 0);
231
232 /* backwards increment the len-bit code huff */
233 incr = 1U << (len - 1);
234 while (huff & incr)
235 incr >>= 1;
236 if (incr != 0) {
237 huff &= incr - 1;
238 huff += incr;
239 }
240 else
241 huff = 0;
242
243 /* go to next symbol, update count, len */
244 sym++;
245 if (--(count[len]) == 0) {
246 if (len == max) break;
247 len = lens[work[sym]];
248 }
249
250 /* create new sub-table if needed */
251 if (len > root && (huff & mask) != low) {
252 /* if first time, transition to sub-tables */
253 if (drop == 0)
254 drop = root;
255
256 /* increment past last table */
257 next += 1U << curr;
258
259 /* determine length of next table */
260 curr = len - drop;
261 left = (int)(1 << curr);
262 while (curr + drop < max) {
263 left -= count[curr + drop];
264 if (left <= 0) break;
265 curr++;
266 left <<= 1;
267 }
268
269 /* check for enough space */
270 used += 1U << curr;
271 if (type == LENS && used >= ENOUGH - MAXD)
272 return 1;
273
274 /* point entry in root table to sub-table */
275 low = huff & mask;
276 (*table)[low].op = (unsigned char)curr;
277 (*table)[low].bits = (unsigned char)root;
278 (*table)[low].val = (unsigned short)(next - *table);
279 }
280 }
281
282 /*
283 Fill in rest of table for incomplete codes. This loop is similar to the
284 loop above in incrementing huff for table indices. It is assumed that
285 len is equal to curr + drop, so there is no loop needed to increment
286 through high index bits. When the current sub-table is filled, the loop
287 drops back to the root table to fill in any remaining entries there.
288 */
289 this.op = (unsigned char)64; /* invalid code marker */
290 this.bits = (unsigned char)(len - drop);
291 this.val = (unsigned short)0;
292 while (huff != 0) {
293 /* when done with sub-table, drop back to root table */
294 if (drop != 0 && (huff & mask) != low) {
295 drop = 0;
296 len = root;
297 next = *table;
298 curr = root;
299 this.bits = (unsigned char)len;
300 }
301
302 /* put invalid code marker in table */
303 next[huff >> drop] = this;
304
305 /* backwards increment the len-bit code huff */
306 incr = 1U << (len - 1);
307 while (huff & incr)
308 incr >>= 1;
309 if (incr != 0) {
310 huff &= incr - 1;
311 huff += incr;
312 }
313 else
314 huff = 0;
315 }
316
317 /* set return parameters */
318 *table += used;
319 *bits = root;
320 return 0;
321}
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