1 /* $NetBSD: inftree9.c,v 1.1.1.1 2006/01/14 20:10:52 christos Exp $ */
2
3 /* inftree9.c -- generate Huffman trees for efficient decoding
4 * Copyright (C) 1995-2005 Mark Adler
5 * For conditions of distribution and use, see copyright notice in zlib.h
6 */
7
8 #include "zutil.h"
9 #include "inftree9.h"
10
11 #define MAXBITS 15
12
13 const char inflate9_copyright[] =
14 " inflate9 1.2.3 Copyright 1995-2005 Mark Adler ";
15 /*
16 If you use the zlib library in a product, an acknowledgment is welcome
17 in the documentation of your product. If for some reason you cannot
18 include such an acknowledgment, I would appreciate that you keep this
19 copyright string in the executable of your product.
20 */
21
22 /*
23 Build a set of tables to decode the provided canonical Huffman code.
24 The code lengths are lens[0..codes-1]. The result starts at *table,
25 whose indices are 0..2^bits-1. work is a writable array of at least
26 lens shorts, which is used as a work area. type is the type of code
27 to be generated, CODES, LENS, or DISTS. On return, zero is success,
28 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
29 on return points to the next available entry's address. bits is the
30 requested root table index bits, and on return it is the actual root
31 table index bits. It will differ if the request is greater than the
32 longest code or if it is less than the shortest code.
33 */
inflate_table9(type,lens,codes,table,bits,work)34 int inflate_table9(type, lens, codes, table, bits, work)
35 codetype type;
36 unsigned short FAR *lens;
37 unsigned codes;
38 code FAR * FAR *table;
39 unsigned FAR *bits;
40 unsigned short FAR *work;
41 {
42 unsigned len; /* a code's length in bits */
43 unsigned sym; /* index of code symbols */
44 unsigned min, max; /* minimum and maximum code lengths */
45 unsigned root; /* number of index bits for root table */
46 unsigned curr; /* number of index bits for current table */
47 unsigned drop; /* code bits to drop for sub-table */
48 int left; /* number of prefix codes available */
49 unsigned used; /* code entries in table used */
50 unsigned huff; /* Huffman code */
51 unsigned incr; /* for incrementing code, index */
52 unsigned fill; /* index for replicating entries */
53 unsigned low; /* low bits for current root entry */
54 unsigned mask; /* mask for low root bits */
55 code this; /* table entry for duplication */
56 code FAR *next; /* next available space in table */
57 const unsigned short FAR *base; /* base value table to use */
58 const unsigned short FAR *extra; /* extra bits table to use */
59 int end; /* use base and extra for symbol > end */
60 unsigned short count[MAXBITS+1]; /* number of codes of each length */
61 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
62 static const unsigned short lbase[31] = { /* Length codes 257..285 base */
63 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17,
64 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115,
65 131, 163, 195, 227, 3, 0, 0};
66 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
67 128, 128, 128, 128, 128, 128, 128, 128, 129, 129, 129, 129,
68 130, 130, 130, 130, 131, 131, 131, 131, 132, 132, 132, 132,
69 133, 133, 133, 133, 144, 201, 196};
70 static const unsigned short dbase[32] = { /* Distance codes 0..31 base */
71 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49,
72 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073,
73 4097, 6145, 8193, 12289, 16385, 24577, 32769, 49153};
74 static const unsigned short dext[32] = { /* Distance codes 0..31 extra */
75 128, 128, 128, 128, 129, 129, 130, 130, 131, 131, 132, 132,
76 133, 133, 134, 134, 135, 135, 136, 136, 137, 137, 138, 138,
77 139, 139, 140, 140, 141, 141, 142, 142};
78
79 /*
80 Process a set of code lengths to create a canonical Huffman code. The
81 code lengths are lens[0..codes-1]. Each length corresponds to the
82 symbols 0..codes-1. The Huffman code is generated by first sorting the
83 symbols by length from short to long, and retaining the symbol order
84 for codes with equal lengths. Then the code starts with all zero bits
85 for the first code of the shortest length, and the codes are integer
86 increments for the same length, and zeros are appended as the length
87 increases. For the deflate format, these bits are stored backwards
88 from their more natural integer increment ordering, and so when the
89 decoding tables are built in the large loop below, the integer codes
90 are incremented backwards.
91
92 This routine assumes, but does not check, that all of the entries in
93 lens[] are in the range 0..MAXBITS. The caller must assure this.
94 1..MAXBITS is interpreted as that code length. zero means that that
95 symbol does not occur in this code.
96
97 The codes are sorted by computing a count of codes for each length,
98 creating from that a table of starting indices for each length in the
99 sorted table, and then entering the symbols in order in the sorted
100 table. The sorted table is work[], with that space being provided by
101 the caller.
102
103 The length counts are used for other purposes as well, i.e. finding
104 the minimum and maximum length codes, determining if there are any
105 codes at all, checking for a valid set of lengths, and looking ahead
106 at length counts to determine sub-table sizes when building the
107 decoding tables.
108 */
109
110 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
111 for (len = 0; len <= MAXBITS; len++)
112 count[len] = 0;
113 for (sym = 0; sym < codes; sym++)
114 count[lens[sym]]++;
115
116 /* bound code lengths, force root to be within code lengths */
117 root = *bits;
118 for (max = MAXBITS; max >= 1; max--)
119 if (count[max] != 0) break;
120 if (root > max) root = max;
121 if (max == 0) return -1; /* no codes! */
122 for (min = 1; min <= MAXBITS; min++)
123 if (count[min] != 0) break;
124 if (root < min) root = min;
125
126 /* check for an over-subscribed or incomplete set of lengths */
127 left = 1;
128 for (len = 1; len <= MAXBITS; len++) {
129 left <<= 1;
130 left -= count[len];
131 if (left < 0) return -1; /* over-subscribed */
132 }
133 if (left > 0 && (type == CODES || max != 1))
134 return -1; /* incomplete set */
135
136 /* generate offsets into symbol table for each length for sorting */
137 offs[1] = 0;
138 for (len = 1; len < MAXBITS; len++)
139 offs[len + 1] = offs[len] + count[len];
140
141 /* sort symbols by length, by symbol order within each length */
142 for (sym = 0; sym < codes; sym++)
143 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
144
145 /*
146 Create and fill in decoding tables. In this loop, the table being
147 filled is at next and has curr index bits. The code being used is huff
148 with length len. That code is converted to an index by dropping drop
149 bits off of the bottom. For codes where len is less than drop + curr,
150 those top drop + curr - len bits are incremented through all values to
151 fill the table with replicated entries.
152
153 root is the number of index bits for the root table. When len exceeds
154 root, sub-tables are created pointed to by the root entry with an index
155 of the low root bits of huff. This is saved in low to check for when a
156 new sub-table should be started. drop is zero when the root table is
157 being filled, and drop is root when sub-tables are being filled.
158
159 When a new sub-table is needed, it is necessary to look ahead in the
160 code lengths to determine what size sub-table is needed. The length
161 counts are used for this, and so count[] is decremented as codes are
162 entered in the tables.
163
164 used keeps track of how many table entries have been allocated from the
165 provided *table space. It is checked when a LENS table is being made
166 against the space in *table, ENOUGH, minus the maximum space needed by
167 the worst case distance code, MAXD. This should never happen, but the
168 sufficiency of ENOUGH has not been proven exhaustively, hence the check.
169 This assumes that when type == LENS, bits == 9.
170
171 sym increments through all symbols, and the loop terminates when
172 all codes of length max, i.e. all codes, have been processed. This
173 routine permits incomplete codes, so another loop after this one fills
174 in the rest of the decoding tables with invalid code markers.
175 */
176
177 /* set up for code type */
178 switch (type) {
179 case CODES:
180 base = extra = work; /* dummy value--not used */
181 end = 19;
182 break;
183 case LENS:
184 base = lbase;
185 base -= 257;
186 extra = lext;
187 extra -= 257;
188 end = 256;
189 break;
190 default: /* DISTS */
191 base = dbase;
192 extra = dext;
193 end = -1;
194 }
195
196 /* initialize state for loop */
197 huff = 0; /* starting code */
198 sym = 0; /* starting code symbol */
199 len = min; /* starting code length */
200 next = *table; /* current table to fill in */
201 curr = root; /* current table index bits */
202 drop = 0; /* current bits to drop from code for index */
203 low = (unsigned)(-1); /* trigger new sub-table when len > root */
204 used = 1U << root; /* use root table entries */
205 mask = used - 1; /* mask for comparing low */
206
207 /* check available table space */
208 if (type == LENS && used >= ENOUGH - MAXD)
209 return 1;
210
211 /* process all codes and make table entries */
212 for (;;) {
213 /* create table entry */
214 this.bits = (unsigned char)(len - drop);
215 if ((int)(work[sym]) < end) {
216 this.op = (unsigned char)0;
217 this.val = work[sym];
218 }
219 else if ((int)(work[sym]) > end) {
220 this.op = (unsigned char)(extra[work[sym]]);
221 this.val = base[work[sym]];
222 }
223 else {
224 this.op = (unsigned char)(32 + 64); /* end of block */
225 this.val = 0;
226 }
227
228 /* replicate for those indices with low len bits equal to huff */
229 incr = 1U << (len - drop);
230 fill = 1U << curr;
231 do {
232 fill -= incr;
233 next[(huff >> drop) + fill] = this;
234 } while (fill != 0);
235
236 /* backwards increment the len-bit code huff */
237 incr = 1U << (len - 1);
238 while (huff & incr)
239 incr >>= 1;
240 if (incr != 0) {
241 huff &= incr - 1;
242 huff += incr;
243 }
244 else
245 huff = 0;
246
247 /* go to next symbol, update count, len */
248 sym++;
249 if (--(count[len]) == 0) {
250 if (len == max) break;
251 len = lens[work[sym]];
252 }
253
254 /* create new sub-table if needed */
255 if (len > root && (huff & mask) != low) {
256 /* if first time, transition to sub-tables */
257 if (drop == 0)
258 drop = root;
259
260 /* increment past last table */
261 next += 1U << curr;
262
263 /* determine length of next table */
264 curr = len - drop;
265 left = (int)(1 << curr);
266 while (curr + drop < max) {
267 left -= count[curr + drop];
268 if (left <= 0) break;
269 curr++;
270 left <<= 1;
271 }
272
273 /* check for enough space */
274 used += 1U << curr;
275 if (type == LENS && used >= ENOUGH - MAXD)
276 return 1;
277
278 /* point entry in root table to sub-table */
279 low = huff & mask;
280 (*table)[low].op = (unsigned char)curr;
281 (*table)[low].bits = (unsigned char)root;
282 (*table)[low].val = (unsigned short)(next - *table);
283 }
284 }
285
286 /*
287 Fill in rest of table for incomplete codes. This loop is similar to the
288 loop above in incrementing huff for table indices. It is assumed that
289 len is equal to curr + drop, so there is no loop needed to increment
290 through high index bits. When the current sub-table is filled, the loop
291 drops back to the root table to fill in any remaining entries there.
292 */
293 this.op = (unsigned char)64; /* invalid code marker */
294 this.bits = (unsigned char)(len - drop);
295 this.val = (unsigned short)0;
296 while (huff != 0) {
297 /* when done with sub-table, drop back to root table */
298 if (drop != 0 && (huff & mask) != low) {
299 drop = 0;
300 len = root;
301 next = *table;
302 curr = root;
303 this.bits = (unsigned char)len;
304 }
305
306 /* put invalid code marker in table */
307 next[huff >> drop] = this;
308
309 /* backwards increment the len-bit code huff */
310 incr = 1U << (len - 1);
311 while (huff & incr)
312 incr >>= 1;
313 if (incr != 0) {
314 huff &= incr - 1;
315 huff += incr;
316 }
317 else
318 huff = 0;
319 }
320
321 /* set return parameters */
322 *table += used;
323 *bits = root;
324 return 0;
325 }
326