Line data Source code
1 : /* $OpenBSD: inftrees.c,v 1.15 2011/07/07 02:57:24 deraadt Exp $ */
2 : /* inftrees.c -- generate Huffman trees for efficient decoding
3 : * Copyright (C) 1995-2005 Mark Adler
4 : * For conditions of distribution and use, see copyright notice in zlib.h
5 : */
6 :
7 : #include "zutil.h"
8 : #include "inftrees.h"
9 :
10 : #define MAXBITS 15
11 :
12 : /*
13 : If you use the zlib library in a product, an acknowledgment is welcome
14 : in the documentation of your product. If for some reason you cannot
15 : include such an acknowledgment, I would appreciate that you keep this
16 : copyright string in the executable of your product.
17 : */
18 :
19 : /*
20 : Build a set of tables to decode the provided canonical Huffman code.
21 : The code lengths are lens[0..codes-1]. The result starts at *table,
22 : whose indices are 0..2^bits-1. work is a writable array of at least
23 : lens shorts, which is used as a work area. type is the type of code
24 : to be generated, CODES, LENS, or DISTS. On return, zero is success,
25 : -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
26 : on return points to the next available entry's address. bits is the
27 : requested root table index bits, and on return it is the actual root
28 : table index bits. It will differ if the request is greater than the
29 : longest code or if it is less than the shortest code.
30 : */
31 0 : int inflate_table(type, lens, codes, table, bits, work)
32 : codetype type;
33 : unsigned short FAR *lens;
34 : unsigned codes;
35 : code FAR * FAR *table;
36 : unsigned FAR *bits;
37 : unsigned short FAR *work;
38 : {
39 : unsigned len; /* a code's length in bits */
40 : unsigned sym; /* index of code symbols */
41 : unsigned min, max; /* minimum and maximum code lengths */
42 : unsigned root; /* number of index bits for root table */
43 : unsigned curr; /* number of index bits for current table */
44 : unsigned drop; /* code bits to drop for sub-table */
45 : int left; /* number of prefix codes available */
46 : unsigned used; /* code entries in table used */
47 : unsigned huff; /* Huffman code */
48 : unsigned incr; /* for incrementing code, index */
49 : unsigned fill; /* index for replicating entries */
50 : unsigned low; /* low bits for current root entry */
51 : unsigned mask; /* mask for low root bits */
52 : code this; /* table entry for duplication */
53 : code FAR *next; /* next available space in table */
54 : const unsigned short FAR *base; /* base value table to use */
55 : const unsigned short FAR *extra; /* extra bits table to use */
56 : int end; /* use base and extra for symbol > end */
57 0 : unsigned short count[MAXBITS+1]; /* number of codes of each length */
58 0 : unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
59 : static const unsigned short lbase[31] = { /* Length codes 257..285 base */
60 : 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
61 : 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
62 : static const unsigned short lext[31] = { /* Length codes 257..285 extra */
63 : 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
64 : 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196};
65 : static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
66 : 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
67 : 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
68 : 8193, 12289, 16385, 24577, 0, 0};
69 : static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
70 : 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
71 : 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
72 : 28, 28, 29, 29, 64, 64};
73 :
74 : /*
75 : Process a set of code lengths to create a canonical Huffman code. The
76 : code lengths are lens[0..codes-1]. Each length corresponds to the
77 : symbols 0..codes-1. The Huffman code is generated by first sorting the
78 : symbols by length from short to long, and retaining the symbol order
79 : for codes with equal lengths. Then the code starts with all zero bits
80 : for the first code of the shortest length, and the codes are integer
81 : increments for the same length, and zeros are appended as the length
82 : increases. For the deflate format, these bits are stored backwards
83 : from their more natural integer increment ordering, and so when the
84 : decoding tables are built in the large loop below, the integer codes
85 : are incremented backwards.
86 :
87 : This routine assumes, but does not check, that all of the entries in
88 : lens[] are in the range 0..MAXBITS. The caller must assure this.
89 : 1..MAXBITS is interpreted as that code length. zero means that that
90 : symbol does not occur in this code.
91 :
92 : The codes are sorted by computing a count of codes for each length,
93 : creating from that a table of starting indices for each length in the
94 : sorted table, and then entering the symbols in order in the sorted
95 : table. The sorted table is work[], with that space being provided by
96 : the caller.
97 :
98 : The length counts are used for other purposes as well, i.e. finding
99 : the minimum and maximum length codes, determining if there are any
100 : codes at all, checking for a valid set of lengths, and looking ahead
101 : at length counts to determine sub-table sizes when building the
102 : decoding tables.
103 : */
104 :
105 : /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
106 0 : for (len = 0; len <= MAXBITS; len++)
107 0 : count[len] = 0;
108 0 : for (sym = 0; sym < codes; sym++)
109 0 : count[lens[sym]]++;
110 :
111 : /* bound code lengths, force root to be within code lengths */
112 0 : root = *bits;
113 0 : for (max = MAXBITS; max >= 1; max--)
114 0 : if (count[max] != 0) break;
115 0 : if (root > max) root = max;
116 0 : if (max == 0) { /* no symbols to code at all */
117 : this.op = (unsigned char)64; /* invalid code marker */
118 : this.bits = (unsigned char)1;
119 : this.val = (unsigned short)0;
120 0 : *(*table)++ = this; /* make a table to force an error */
121 0 : *(*table)++ = this;
122 0 : *bits = 1;
123 0 : return 0; /* no symbols, but wait for decoding to report error */
124 : }
125 0 : for (min = 1; min <= MAXBITS; min++)
126 0 : if (count[min] != 0) break;
127 0 : if (root < min) root = min;
128 :
129 : /* check for an over-subscribed or incomplete set of lengths */
130 : left = 1;
131 0 : for (len = 1; len <= MAXBITS; len++) {
132 0 : left <<= 1;
133 0 : left -= count[len];
134 0 : if (left < 0) return -1; /* over-subscribed */
135 : }
136 0 : if (left > 0 && (type == CODES || max != 1))
137 0 : return -1; /* incomplete set */
138 :
139 : /* generate offsets into symbol table for each length for sorting */
140 0 : offs[1] = 0;
141 0 : for (len = 1; len < MAXBITS; len++)
142 0 : offs[len + 1] = offs[len] + count[len];
143 :
144 : /* sort symbols by length, by symbol order within each length */
145 0 : for (sym = 0; sym < codes; sym++)
146 0 : if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
147 :
148 : /*
149 : Create and fill in decoding tables. In this loop, the table being
150 : filled is at next and has curr index bits. The code being used is huff
151 : with length len. That code is converted to an index by dropping drop
152 : bits off of the bottom. For codes where len is less than drop + curr,
153 : those top drop + curr - len bits are incremented through all values to
154 : fill the table with replicated entries.
155 :
156 : root is the number of index bits for the root table. When len exceeds
157 : root, sub-tables are created pointed to by the root entry with an index
158 : of the low root bits of huff. This is saved in low to check for when a
159 : new sub-table should be started. drop is zero when the root table is
160 : being filled, and drop is root when sub-tables are being filled.
161 :
162 : When a new sub-table is needed, it is necessary to look ahead in the
163 : code lengths to determine what size sub-table is needed. The length
164 : counts are used for this, and so count[] is decremented as codes are
165 : entered in the tables.
166 :
167 : used keeps track of how many table entries have been allocated from the
168 : provided *table space. It is checked when a LENS table is being made
169 : against the space in *table, ENOUGH, minus the maximum space needed by
170 : the worst case distance code, MAXD. This should never happen, but the
171 : sufficiency of ENOUGH has not been proven exhaustively, hence the check.
172 : This assumes that when type == LENS, bits == 9.
173 :
174 : sym increments through all symbols, and the loop terminates when
175 : all codes of length max, i.e. all codes, have been processed. This
176 : routine permits incomplete codes, so another loop after this one fills
177 : in the rest of the decoding tables with invalid code markers.
178 : */
179 :
180 : /* set up for code type */
181 0 : switch (type) {
182 : case CODES:
183 : base = extra = work; /* dummy value--not used */
184 : end = 19;
185 0 : break;
186 : case LENS:
187 : base = lbase;
188 : base -= 257;
189 : extra = lext;
190 : extra -= 257;
191 : end = 256;
192 0 : break;
193 : default: /* DISTS */
194 : base = dbase;
195 : extra = dext;
196 : end = -1;
197 0 : }
198 :
199 : /* initialize state for loop */
200 : huff = 0; /* starting code */
201 : sym = 0; /* starting code symbol */
202 : len = min; /* starting code length */
203 0 : next = *table; /* current table to fill in */
204 : curr = root; /* current table index bits */
205 : drop = 0; /* current bits to drop from code for index */
206 : low = (unsigned)(-1); /* trigger new sub-table when len > root */
207 0 : used = 1U << root; /* use root table entries */
208 0 : mask = used - 1; /* mask for comparing low */
209 :
210 : /* check available table space */
211 0 : if (type == LENS && used >= ENOUGH - MAXD)
212 0 : return 1;
213 :
214 : /* process all codes and make table entries */
215 0 : for (;;) {
216 : /* create table entry */
217 0 : this.bits = (unsigned char)(len - drop);
218 0 : if ((int)(work[sym]) < end) {
219 : this.op = (unsigned char)0;
220 : this.val = work[sym];
221 0 : }
222 0 : else if ((int)(work[sym]) > end) {
223 0 : this.op = (unsigned char)(extra[work[sym]]);
224 0 : this.val = base[work[sym]];
225 0 : }
226 : else {
227 : this.op = (unsigned char)(32 + 64); /* end of block */
228 : this.val = 0;
229 : }
230 :
231 : /* replicate for those indices with low len bits equal to huff */
232 0 : incr = 1U << (len - drop);
233 0 : fill = 1U << curr;
234 : min = fill; /* save offset to next table */
235 0 : do {
236 0 : fill -= incr;
237 0 : next[(huff >> drop) + fill] = this;
238 0 : } while (fill != 0);
239 :
240 : /* backwards increment the len-bit code huff */
241 0 : incr = 1U << (len - 1);
242 0 : while (huff & incr)
243 0 : incr >>= 1;
244 0 : if (incr != 0) {
245 0 : huff &= incr - 1;
246 0 : huff += incr;
247 0 : }
248 : else
249 : huff = 0;
250 :
251 : /* go to next symbol, update count, len */
252 0 : sym++;
253 0 : if (--(count[len]) == 0) {
254 0 : if (len == max) break;
255 0 : len = lens[work[sym]];
256 0 : }
257 :
258 : /* create new sub-table if needed */
259 0 : if (len > root && (huff & mask) != low) {
260 : /* if first time, transition to sub-tables */
261 0 : if (drop == 0)
262 0 : drop = root;
263 :
264 : /* increment past last table */
265 0 : next += min; /* here min is 1 << curr */
266 :
267 : /* determine length of next table */
268 0 : curr = len - drop;
269 0 : left = (int)(1 << curr);
270 0 : while (curr + drop < max) {
271 0 : left -= count[curr + drop];
272 0 : if (left <= 0) break;
273 0 : curr++;
274 0 : left <<= 1;
275 : }
276 :
277 : /* check for enough space */
278 0 : used += 1U << curr;
279 0 : if (type == LENS && used >= ENOUGH - MAXD)
280 0 : return 1;
281 :
282 : /* point entry in root table to sub-table */
283 : low = huff & mask;
284 0 : (*table)[low].op = (unsigned char)curr;
285 0 : (*table)[low].bits = (unsigned char)root;
286 0 : (*table)[low].val = (unsigned short)(next - *table);
287 0 : }
288 : }
289 :
290 : /*
291 : Fill in rest of table for incomplete codes. This loop is similar to the
292 : loop above in incrementing huff for table indices. It is assumed that
293 : len is equal to curr + drop, so there is no loop needed to increment
294 : through high index bits. When the current sub-table is filled, the loop
295 : drops back to the root table to fill in any remaining entries there.
296 : */
297 : this.op = (unsigned char)64; /* invalid code marker */
298 : this.bits = (unsigned char)(len - drop);
299 : this.val = (unsigned short)0;
300 0 : while (huff != 0) {
301 : /* when done with sub-table, drop back to root table */
302 0 : if (drop != 0 && (huff & mask) != low) {
303 : drop = 0;
304 : len = root;
305 0 : next = *table;
306 0 : this.bits = (unsigned char)len;
307 0 : }
308 :
309 : /* put invalid code marker in table */
310 0 : next[huff >> drop] = this;
311 :
312 : /* backwards increment the len-bit code huff */
313 0 : incr = 1U << (len - 1);
314 0 : while (huff & incr)
315 0 : incr >>= 1;
316 0 : if (incr != 0) {
317 0 : huff &= incr - 1;
318 0 : huff += incr;
319 0 : }
320 : else
321 : huff = 0;
322 : }
323 :
324 : /* set return parameters */
325 0 : *table += used;
326 0 : *bits = root;
327 0 : return 0;
328 0 : }
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