1 /* $OpenBSD: inftrees.c,v 1.14 2005/07/20 15:56:46 millert 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 const char inflate_copyright[] =
13 " inflate 1.2.3 Copyright 1995-2005 Mark Adler ";
14 /*
15 If you use the zlib library in a product, an acknowledgment is welcome
16 in the documentation of your product. If for some reason you cannot
17 include such an acknowledgment, I would appreciate that you keep this
18 copyright string in the executable of your product.
19 */
20
21 /*
22 Build a set of tables to decode the provided canonical Huffman code.
23 The code lengths are lens[0..codes-1]. The result starts at *table,
24 whose indices are 0..2^bits-1. work is a writable array of at least
25 lens shorts, which is used as a work area. type is the type of code
26 to be generated, CODES, LENS, or DISTS. On return, zero is success,
27 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
28 on return points to the next available entry's address. bits is the
29 requested root table index bits, and on return it is the actual root
30 table index bits. It will differ if the request is greater than the
31 longest code or if it is less than the shortest code.
32 */
33 int inflate_table(type, lens, codes, table, bits, work)
34 codetype type;
35 unsigned short FAR *lens;
36 unsigned codes;
37 code FAR * FAR *table;
38 unsigned FAR *bits;
39 unsigned short FAR *work;
40 {
41 unsigned len; /* a code's length in bits */
42 unsigned sym; /* index of code symbols */
43 unsigned min, max; /* minimum and maximum code lengths */
44 unsigned root; /* number of index bits for root table */
45 unsigned curr; /* number of index bits for current table */
46 unsigned drop; /* code bits to drop for sub-table */
47 int left; /* number of prefix codes available */
48 unsigned used; /* code entries in table used */
49 unsigned huff; /* Huffman code */
50 unsigned incr; /* for incrementing code, index */
51 unsigned fill; /* index for replicating entries */
52 unsigned low; /* low bits for current root entry */
53 unsigned mask; /* mask for low root bits */
54 code this; /* table entry for duplication */
55 code FAR *next; /* next available space in table */
56 const unsigned short FAR *base; /* base value table to use */
57 const unsigned short FAR *extra; /* extra bits table to use */
58 int end; /* use base and extra for symbol > end */
59 unsigned short count[MAXBITS+1]; /* number of codes of each length */
60 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
61 static const unsigned short lbase[31] = { /* Length codes 257..285 base */
62 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
63 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
64 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
65 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
66 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196};
67 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
68 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
69 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
70 8193, 12289, 16385, 24577, 0, 0};
71 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
72 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
73 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
74 28, 28, 29, 29, 64, 64};
75
76 /*
77 Process a set of code lengths to create a canonical Huffman code. The
78 code lengths are lens[0..codes-1]. Each length corresponds to the
79 symbols 0..codes-1. The Huffman code is generated by first sorting the
80 symbols by length from short to long, and retaining the symbol order
81 for codes with equal lengths. Then the code starts with all zero bits
82 for the first code of the shortest length, and the codes are integer
83 increments for the same length, and zeros are appended as the length
84 increases. For the deflate format, these bits are stored backwards
85 from their more natural integer increment ordering, and so when the
86 decoding tables are built in the large loop below, the integer codes
87 are incremented backwards.
88
89 This routine assumes, but does not check, that all of the entries in
90 lens[] are in the range 0..MAXBITS. The caller must assure this.
91 1..MAXBITS is interpreted as that code length. zero means that that
92 symbol does not occur in this code.
93
94 The codes are sorted by computing a count of codes for each length,
95 creating from that a table of starting indices for each length in the
96 sorted table, and then entering the symbols in order in the sorted
97 table. The sorted table is work[], with that space being provided by
98 the caller.
99
100 The length counts are used for other purposes as well, i.e. finding
101 the minimum and maximum length codes, determining if there are any
102 codes at all, checking for a valid set of lengths, and looking ahead
103 at length counts to determine sub-table sizes when building the
104 decoding tables.
105 */
106
107 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
108 for (len = 0; len <= MAXBITS; len++)
109 count[len] = 0;
110 for (sym = 0; sym < codes; sym++)
111 count[lens[sym]]++;
112
113 /* bound code lengths, force root to be within code lengths */
114 root = *bits;
115 for (max = MAXBITS; max >= 1; max--)
116 if (count[max] != 0) break;
117 if (root > max) root = max;
118 if (max == 0) { /* no symbols to code at all */
119 this.op = (unsigned char)64; /* invalid code marker */
120 this.bits = (unsigned char)1;
121 this.val = (unsigned short)0;
122 *(*table)++ = this; /* make a table to force an error */
123 *(*table)++ = this;
124 *bits = 1;
125 return 0; /* no symbols, but wait for decoding to report error */
126 }
127 for (min = 1; min <= MAXBITS; min++)
128 if (count[min] != 0) break;
129 if (root < min) root = min;
130
131 /* check for an over-subscribed or incomplete set of lengths */
132 left = 1;
133 for (len = 1; len <= MAXBITS; len++) {
134 left <<= 1;
135 left -= count[len];
136 if (left < 0) return -1; /* over-subscribed */
137 }
138 if (left > 0 && (type == CODES || max != 1))
139 return -1; /* incomplete set */
140
141 /* generate offsets into symbol table for each length for sorting */
142 offs[1] = 0;
143 for (len = 1; len < MAXBITS; len++)
144 offs[len + 1] = offs[len] + count[len];
145
146 /* sort symbols by length, by symbol order within each length */
147 for (sym = 0; sym < codes; sym++)
148 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
149
150 /*
151 Create and fill in decoding tables. In this loop, the table being
152 filled is at next and has curr index bits. The code being used is huff
153 with length len. That code is converted to an index by dropping drop
154 bits off of the bottom. For codes where len is less than drop + curr,
155 those top drop + curr - len bits are incremented through all values to
156 fill the table with replicated entries.
157
158 root is the number of index bits for the root table. When len exceeds
159 root, sub-tables are created pointed to by the root entry with an index
160 of the low root bits of huff. This is saved in low to check for when a
161 new sub-table should be started. drop is zero when the root table is
162 being filled, and drop is root when sub-tables are being filled.
163
164 When a new sub-table is needed, it is necessary to look ahead in the
165 code lengths to determine what size sub-table is needed. The length
166 counts are used for this, and so count[] is decremented as codes are
167 entered in the tables.
168
169 used keeps track of how many table entries have been allocated from the
170 provided *table space. It is checked when a LENS table is being made
171 against the space in *table, ENOUGH, minus the maximum space needed by
172 the worst case distance code, MAXD. This should never happen, but the
173 sufficiency of ENOUGH has not been proven exhaustively, hence the check.
174 This assumes that when type == LENS, bits == 9.
175
176 sym increments through all symbols, and the loop terminates when
177 all codes of length max, i.e. all codes, have been processed. This
178 routine permits incomplete codes, so another loop after this one fills
179 in the rest of the decoding tables with invalid code markers.
180 */
181
182 /* set up for code type */
183 switch (type) {
184 case CODES:
185 base = extra = work; /* dummy value--not used */
186 end = 19;
187 break;
188 case LENS:
189 base = lbase;
190 base -= 257;
191 extra = lext;
192 extra -= 257;
193 end = 256;
194 break;
195 default: /* DISTS */
196 base = dbase;
197 extra = dext;
198 end = -1;
199 }
200
201 /* initialize state for loop */
202 huff = 0; /* starting code */
203 sym = 0; /* starting code symbol */
204 len = min; /* starting code length */
205 next = *table; /* current table to fill in */
206 curr = root; /* current table index bits */
207 drop = 0; /* current bits to drop from code for index */
208 low = (unsigned)(-1); /* trigger new sub-table when len > root */
209 used = 1U << root; /* use root table entries */
210 mask = used - 1; /* mask for comparing low */
211
212 /* check available table space */
213 if (type == LENS && used >= ENOUGH - MAXD)
214 return 1;
215
216 /* process all codes and make table entries */
217 for (;;) {
218 /* create table entry */
219 this.bits = (unsigned char)(len - drop);
220 if ((int)(work[sym]) < end) {
221 this.op = (unsigned char)0;
222 this.val = work[sym];
223 }
224 else if ((int)(work[sym]) > end) {
225 this.op = (unsigned char)(extra[work[sym]]);
226 this.val = base[work[sym]];
227 }
228 else {
229 this.op = (unsigned char)(32 + 64); /* end of block */
230 this.val = 0;
231 }
232
233 /* replicate for those indices with low len bits equal to huff */
234 incr = 1U << (len - drop);
235 fill = 1U << curr;
236 min = fill; /* save offset to next table */
237 do {
238 fill -= incr;
239 next[(huff >> drop) + fill] = this;
240 } while (fill != 0);
241
242 /* backwards increment the len-bit code huff */
243 incr = 1U << (len - 1);
244 while (huff & incr)
245 incr >>= 1;
246 if (incr != 0) {
247 huff &= incr - 1;
248 huff += incr;
249 }
250 else
251 huff = 0;
252
253 /* go to next symbol, update count, len */
254 sym++;
255 if (--(count[len]) == 0) {
256 if (len == max) break;
257 len = lens[work[sym]];
258 }
259
260 /* create new sub-table if needed */
261 if (len > root && (huff & mask) != low) {
262 /* if first time, transition to sub-tables */
263 if (drop == 0)
264 drop = root;
265
266 /* increment past last table */
267 next += min; /* here min is 1 << curr */
268
269 /* determine length of next table */
270 curr = len - drop;
271 left = (int)(1 << curr);
272 while (curr + drop < max) {
273 left -= count[curr + drop];
274 if (left <= 0) break;
275 curr++;
276 left <<= 1;
277 }
278
279 /* check for enough space */
280 used += 1U << curr;
281 if (type == LENS && used >= ENOUGH - MAXD)
282 return 1;
283
284 /* point entry in root table to sub-table */
285 low = huff & mask;
286 (*table)[low].op = (unsigned char)curr;
287 (*table)[low].bits = (unsigned char)root;
288 (*table)[low].val = (unsigned short)(next - *table);
289 }
290 }
291
292 /*
293 Fill in rest of table for incomplete codes. This loop is similar to the
294 loop above in incrementing huff for table indices. It is assumed that
295 len is equal to curr + drop, so there is no loop needed to increment
296 through high index bits. When the current sub-table is filled, the loop
297 drops back to the root table to fill in any remaining entries there.
298 */
299 this.op = (unsigned char)64; /* invalid code marker */
300 this.bits = (unsigned char)(len - drop);
301 this.val = (unsigned short)0;
302 while (huff != 0) {
303 /* when done with sub-table, drop back to root table */
304 if (drop != 0 && (huff & mask) != low) {
305 drop = 0;
306 len = root;
307 next = *table;
308 this.bits = (unsigned char)len;
309 }
310
311 /* put invalid code marker in table */
312 next[huff >> drop] = this;
313
314 /* backwards increment the len-bit code huff */
315 incr = 1U << (len - 1);
316 while (huff & incr)
317 incr >>= 1;
318 if (incr != 0) {
319 huff &= incr - 1;
320 huff += incr;
321 }
322 else
323 huff = 0;
324 }
325
326 /* set return parameters */
327 *table += used;
328 *bits = root;
329 return 0;
330 }