1 /* inftrees.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2005 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
11 const char inflate_copyright[] =
12 " inflate 1.2.3 Copyright 1995-2005 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 */
inflate_table(codetype type,unsigned short FAR * lens,unsigned codes,code FAR * FAR * table,unsigned FAR * bits,unsigned short FAR * work)32 int inflate_table (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 thisx; /* 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 unsigned short count[MAXBITS+1]; /* number of codes of each length */
58 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 for (len = 0; len <= MAXBITS; len++)
107 count[len] = 0;
108 for (sym = 0; sym < codes; sym++)
109 count[lens[sym]]++;
110
111 /* bound code lengths, force root to be within code lengths */
112 root = *bits;
113 for (max = MAXBITS; max >= 1; max--)
114 if (count[max] != 0) break;
115 if (root > max) root = max;
116 if (max == 0) { /* no symbols to code at all */
117 thisx.op = (unsigned char)64; /* invalid code marker */
118 thisx.bits = (unsigned char)1;
119 thisx.val = (unsigned short)0;
120 *(*table)++ = thisx; /* make a table to force an error */
121 *(*table)++ = thisx;
122 *bits = 1;
123 return 0; /* no symbols, but wait for decoding to report error */
124 }
125 for (min = 1; min <= MAXBITS; min++)
126 if (count[min] != 0) break;
127 if (root < min) root = min;
128
129 /* check for an over-subscribed or incomplete set of lengths */
130 left = 1;
131 for (len = 1; len <= MAXBITS; len++) {
132 left <<= 1;
133 left -= count[len];
134 if (left < 0) return -1; /* over-subscribed */
135 }
136 if (left > 0 && (type == CODES || max != 1))
137 return -1; /* incomplete set */
138
139 /* generate offsets into symbol table for each length for sorting */
140 offs[1] = 0;
141 for (len = 1; len < MAXBITS; len++)
142 offs[len + 1] = offs[len] + count[len];
143
144 /* sort symbols by length, by symbol order within each length */
145 for (sym = 0; sym < codes; sym++)
146 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 switch (type) {
182 case CODES:
183 base = extra = work; /* dummy value--not used */
184 end = 19;
185 break;
186 case LENS:
187 base = lbase;
188 base -= 257;
189 extra = lext;
190 extra -= 257;
191 end = 256;
192 break;
193 default: /* DISTS */
194 base = dbase;
195 extra = dext;
196 end = -1;
197 }
198
199 /* initialize state for loop */
200 huff = 0; /* starting code */
201 sym = 0; /* starting code symbol */
202 len = min; /* starting code length */
203 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 used = 1U << root; /* use root table entries */
208 mask = used - 1; /* mask for comparing low */
209
210 /* check available table space */
211 if (type == LENS && used >= ENOUGH - MAXD)
212 return 1;
213
214 /* process all codes and make table entries */
215 for (;;) {
216 /* create table entry */
217 thisx.bits = (unsigned char)(len - drop);
218 if ((int)(work[sym]) < end) {
219 thisx.op = (unsigned char)0;
220 thisx.val = work[sym];
221 }
222 else if ((int)(work[sym]) > end) {
223 thisx.op = (unsigned char)(extra[work[sym]]);
224 thisx.val = base[work[sym]];
225 }
226 else {
227 thisx.op = (unsigned char)(32 + 64); /* end of block */
228 thisx.val = 0;
229 }
230
231 /* replicate for those indices with low len bits equal to huff */
232 incr = 1U << (len - drop);
233 fill = 1U << curr;
234 min = fill; /* save offset to next table */
235 do {
236 fill -= incr;
237 next[(huff >> drop) + fill] = thisx;
238 } while (fill != 0);
239
240 /* backwards increment the len-bit code huff */
241 incr = 1U << (len - 1);
242 while (huff & incr)
243 incr >>= 1;
244 if (incr != 0) {
245 huff &= incr - 1;
246 huff += incr;
247 }
248 else
249 huff = 0;
250
251 /* go to next symbol, update count, len */
252 sym++;
253 if (--(count[len]) == 0) {
254 if (len == max) break;
255 len = lens[work[sym]];
256 }
257
258 /* create new sub-table if needed */
259 if (len > root && (huff & mask) != low) {
260 /* if first time, transition to sub-tables */
261 if (drop == 0)
262 drop = root;
263
264 /* increment past last table */
265 next += min; /* here min is 1 << curr */
266
267 /* determine length of next table */
268 curr = len - drop;
269 left = (int)(1 << curr);
270 while (curr + drop < max) {
271 left -= count[curr + drop];
272 if (left <= 0) break;
273 curr++;
274 left <<= 1;
275 }
276
277 /* check for enough space */
278 used += 1U << curr;
279 if (type == LENS && used >= ENOUGH - MAXD)
280 return 1;
281
282 /* point entry in root table to sub-table */
283 low = huff & mask;
284 (*table)[low].op = (unsigned char)curr;
285 (*table)[low].bits = (unsigned char)root;
286 (*table)[low].val = (unsigned short)(next - *table);
287 }
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 thisx.op = (unsigned char)64; /* invalid code marker */
298 thisx.bits = (unsigned char)(len - drop);
299 thisx.val = (unsigned short)0;
300 while (huff != 0) {
301 /* when done with sub-table, drop back to root table */
302 if (drop != 0 && (huff & mask) != low) {
303 drop = 0;
304 len = root;
305 next = *table;
306 thisx.bits = (unsigned char)len;
307 }
308
309 /* put invalid code marker in table */
310 next[huff >> drop] = thisx;
311
312 /* backwards increment the len-bit code huff */
313 incr = 1U << (len - 1);
314 while (huff & incr)
315 incr >>= 1;
316 if (incr != 0) {
317 huff &= incr - 1;
318 huff += incr;
319 }
320 else
321 huff = 0;
322 }
323
324 /* set return parameters */
325 *table += used;
326 *bits = root;
327 return 0;
328 }
329