Line data Source code
1 : /* inftrees.c -- generate Huffman trees for efficient decoding
2 : * Copyright (C) 1995-2017 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 1.2.11 Copyright 1995-2017 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 : */
32 525 : int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work)
33 : codetype type;
34 : unsigned short FAR *lens;
35 : unsigned codes;
36 : code FAR * FAR *table;
37 : unsigned FAR *bits;
38 : unsigned 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 here; /* 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 : unsigned match; /* use base and extra for symbol >= match */
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, 77, 202};
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 8925 : for (len = 0; len <= MAXBITS; len++)
108 8400 : count[len] = 0;
109 57575 : for (sym = 0; sym < codes; sym++)
110 57050 : count[lens[sym]]++;
111 :
112 : /* bound code lengths, force root to be within code lengths */
113 525 : root = *bits;
114 3897 : for (max = MAXBITS; max >= 1; max--)
115 3897 : if (count[max] != 0) break;
116 525 : if (root > max) root = max;
117 525 : if (max == 0) { /* no symbols to code at all */
118 0 : here.op = (unsigned char)64; /* invalid code marker */
119 0 : here.bits = (unsigned char)1;
120 0 : here.val = (unsigned short)0;
121 0 : *(*table)++ = here; /* make a table to force an error */
122 0 : *(*table)++ = here;
123 0 : *bits = 1;
124 0 : return 0; /* no symbols, but wait for decoding to report error */
125 : }
126 1453 : for (min = 1; min < max; min++)
127 1447 : if (count[min] != 0) break;
128 525 : if (root < min) root = min;
129 :
130 : /* check for an over-subscribed or incomplete set of lengths */
131 525 : left = 1;
132 8400 : for (len = 1; len <= MAXBITS; len++) {
133 7875 : left <<= 1;
134 7875 : left -= count[len];
135 7875 : if (left < 0) return -1; /* over-subscribed */
136 : }
137 525 : if (left > 0 && (type == CODES || max != 1))
138 0 : return -1; /* incomplete set */
139 :
140 : /* generate offsets into symbol table for each length for sorting */
141 525 : offs[1] = 0;
142 7875 : for (len = 1; len < MAXBITS; len++)
143 7350 : offs[len + 1] = offs[len] + count[len];
144 :
145 : /* sort symbols by length, by symbol order within each length */
146 57575 : for (sym = 0; sym < codes; sym++)
147 57050 : if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
148 :
149 : /*
150 : Create and fill in decoding tables. In this loop, the table being
151 : filled is at next and has curr index bits. The code being used is huff
152 : with length len. That code is converted to an index by dropping drop
153 : bits off of the bottom. For codes where len is less than drop + curr,
154 : those top drop + curr - len bits are incremented through all values to
155 : fill the table with replicated entries.
156 :
157 : root is the number of index bits for the root table. When len exceeds
158 : root, sub-tables are created pointed to by the root entry with an index
159 : of the low root bits of huff. This is saved in low to check for when a
160 : new sub-table should be started. drop is zero when the root table is
161 : being filled, and drop is root when sub-tables are being filled.
162 :
163 : When a new sub-table is needed, it is necessary to look ahead in the
164 : code lengths to determine what size sub-table is needed. The length
165 : counts are used for this, and so count[] is decremented as codes are
166 : entered in the tables.
167 :
168 : used keeps track of how many table entries have been allocated from the
169 : provided *table space. It is checked for LENS and DIST tables against
170 : the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
171 : the initial root table size constants. See the comments in inftrees.h
172 : for more information.
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 */
181 525 : switch (type) {
182 : case CODES:
183 175 : base = extra = work; /* dummy value--not used */
184 175 : match = 20;
185 175 : break;
186 : case LENS:
187 175 : base = lbase;
188 175 : extra = lext;
189 175 : match = 257;
190 175 : break;
191 : default: /* DISTS */
192 175 : base = dbase;
193 175 : extra = dext;
194 175 : match = 0;
195 : }
196 :
197 : /* initialize state for loop */
198 525 : huff = 0; /* starting code */
199 525 : sym = 0; /* starting code symbol */
200 525 : len = min; /* starting code length */
201 525 : next = *table; /* current table to fill in */
202 525 : curr = root; /* current table index bits */
203 525 : drop = 0; /* current bits to drop from code for index */
204 525 : low = (unsigned)(-1); /* trigger new sub-table when len > root */
205 525 : used = 1U << root; /* use root table entries */
206 525 : mask = used - 1; /* mask for comparing low */
207 :
208 : /* check available table space */
209 525 : if ((type == LENS && used > ENOUGH_LENS) ||
210 175 : (type == DISTS && used > ENOUGH_DISTS))
211 0 : return 1;
212 :
213 : /* process all codes and make table entries */
214 : for (;;) {
215 : /* create table entry */
216 86731 : here.bits = (unsigned char)(len - drop);
217 43628 : if (work[sym] + 1U < match) {
218 35310 : here.op = (unsigned char)0;
219 35310 : here.val = work[sym];
220 : }
221 8318 : else if (work[sym] >= match) {
222 8143 : here.op = (unsigned char)(extra[work[sym] - match]);
223 8143 : here.val = base[work[sym] - match];
224 : }
225 : else {
226 175 : here.op = (unsigned char)(32 + 64); /* end of block */
227 175 : here.val = 0;
228 : }
229 :
230 : /* replicate for those indices with low len bits equal to huff */
231 43628 : incr = 1U << (len - drop);
232 43628 : fill = 1U << curr;
233 43628 : min = fill; /* save offset to next table */
234 : do {
235 128301 : fill -= incr;
236 128301 : next[(huff >> drop) + fill] = here;
237 128301 : } while (fill != 0);
238 :
239 : /* backwards increment the len-bit code huff */
240 43628 : incr = 1U << (len - 1);
241 130359 : while (huff & incr)
242 43103 : incr >>= 1;
243 43628 : if (incr != 0) {
244 43103 : huff &= incr - 1;
245 43103 : huff += incr;
246 : }
247 : else
248 525 : huff = 0;
249 :
250 : /* go to next symbol, update count, len */
251 43628 : sym++;
252 43628 : if (--(count[len]) == 0) {
253 3475 : if (len == max) break;
254 2950 : len = lens[work[sym]];
255 : }
256 :
257 : /* create new sub-table if needed */
258 43103 : if (len > root && (huff & mask) != low) {
259 : /* if first time, transition to sub-tables */
260 5935 : if (drop == 0)
261 318 : drop = root;
262 :
263 : /* increment past last table */
264 5935 : next += min; /* here min is 1 << curr */
265 :
266 : /* determine length of next table */
267 5935 : curr = len - drop;
268 5935 : left = (int)(1 << curr);
269 12263 : while (curr + drop < max) {
270 4774 : left -= count[curr + drop];
271 4774 : if (left <= 0) break;
272 393 : curr++;
273 393 : left <<= 1;
274 : }
275 :
276 : /* check for enough space */
277 5935 : used += 1U << curr;
278 5935 : if ((type == LENS && used > ENOUGH_LENS) ||
279 206 : (type == DISTS && used > ENOUGH_DISTS))
280 0 : return 1;
281 :
282 : /* point entry in root table to sub-table */
283 5935 : low = huff & mask;
284 5935 : (*table)[low].op = (unsigned char)curr;
285 5935 : (*table)[low].bits = (unsigned char)root;
286 5935 : (*table)[low].val = (unsigned short)(next - *table);
287 : }
288 : }
289 :
290 : /* fill in remaining table entry if code is incomplete (guaranteed to have
291 : at most one remaining entry, since if the code is incomplete, the
292 : maximum code length that was allowed to get this far is one bit) */
293 525 : if (huff != 0) {
294 0 : here.op = (unsigned char)64; /* invalid code marker */
295 0 : here.bits = (unsigned char)(len - drop);
296 0 : here.val = (unsigned short)0;
297 0 : next[huff] = here;
298 : }
299 :
300 : /* set return parameters */
301 525 : *table += used;
302 525 : *bits = root;
303 525 : return 0;
304 : }
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