1 /*
2 * Copyright (c) 2008-2016, 2020 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
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14 *
15 * Please obtain a copy of the License at
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27 */
28 /* inftrees.c -- generate Huffman trees for efficient decoding
29 * Copyright (C) 1995-2005 Mark Adler
30 * For conditions of distribution and use, see copyright notice in zlib.h
31 */
32
33 #include "zutil.h"
34 #include "inftrees.h"
35
36 #define MAXBITS 15
37
38 const char inflate_copyright[] =
39 " inflate 1.2.3 Copyright 1995-2005 Mark Adler ";
40 /*
41 If you use the zlib library in a product, an acknowledgment is welcome
42 in the documentation of your product. If for some reason you cannot
43 include such an acknowledgment, I would appreciate that you keep this
44 copyright string in the executable of your product.
45 */
46
47 /*
48 Build a set of tables to decode the provided canonical Huffman code.
49 The code lengths are lens[0..codes-1]. The result starts at *table,
50 whose indices are 0..2^bits-1. work is a writable array of at least
51 lens shorts, which is used as a work area. type is the type of code
52 to be generated, CODES, LENS, or DISTS. On return, zero is success,
53 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
54 on return points to the next available entry's address. bits is the
55 requested root table index bits, and on return it is the actual root
56 table index bits. It will differ if the request is greater than the
57 longest code or if it is less than the shortest code.
58 */
59 int
inflate_table(codetype type,unsigned short FAR * lens,unsigned codes,code FAR * FAR * table,unsigned FAR * bits,unsigned short FAR * work)60 inflate_table(codetype type, unsigned short FAR *lens, unsigned codes,
61 code FAR * FAR *table, unsigned FAR *bits,
62 unsigned short FAR *work)
63 {
64 unsigned len; /* a code's length in bits */
65 unsigned sym; /* index of code symbols */
66 unsigned min, max; /* minimum and maximum code lengths */
67 unsigned root; /* number of index bits for root table */
68 unsigned curr; /* number of index bits for current table */
69 unsigned drop; /* code bits to drop for sub-table */
70 int left; /* number of prefix codes available */
71 unsigned used; /* code entries in table used */
72 unsigned huff; /* Huffman code */
73 unsigned incr; /* for incrementing code, index */
74 unsigned fill; /* index for replicating entries */
75 unsigned low; /* low bits for current root entry */
76 unsigned mask; /* mask for low root bits */
77 code this; /* table entry for duplication */
78 code FAR *next; /* next available space in table */
79 const unsigned short FAR *base; /* base value table to use */
80 const unsigned short FAR *extra; /* extra bits table to use */
81 unsigned match; /* use base and extra for symbol >= match */
82 unsigned short count[MAXBITS+1]; /* number of codes of each length */
83 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
84 static const unsigned short lbase[31] = { /* Length codes 257..285 base */
85 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
86 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
87 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
88 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
89 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196};
90 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
91 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
92 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
93 8193, 12289, 16385, 24577, 0, 0};
94 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
95 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
96 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
97 28, 28, 29, 29, 64, 64};
98
99 /*
100 Process a set of code lengths to create a canonical Huffman code. The
101 code lengths are lens[0..codes-1]. Each length corresponds to the
102 symbols 0..codes-1. The Huffman code is generated by first sorting the
103 symbols by length from short to long, and retaining the symbol order
104 for codes with equal lengths. Then the code starts with all zero bits
105 for the first code of the shortest length, and the codes are integer
106 increments for the same length, and zeros are appended as the length
107 increases. For the deflate format, these bits are stored backwards
108 from their more natural integer increment ordering, and so when the
109 decoding tables are built in the large loop below, the integer codes
110 are incremented backwards.
111
112 This routine assumes, but does not check, that all of the entries in
113 lens[] are in the range 0..MAXBITS. The caller must assure this.
114 1..MAXBITS is interpreted as that code length. zero means that that
115 symbol does not occur in this code.
116
117 The codes are sorted by computing a count of codes for each length,
118 creating from that a table of starting indices for each length in the
119 sorted table, and then entering the symbols in order in the sorted
120 table. The sorted table is work[], with that space being provided by
121 the caller.
122
123 The length counts are used for other purposes as well, i.e. finding
124 the minimum and maximum length codes, determining if there are any
125 codes at all, checking for a valid set of lengths, and looking ahead
126 at length counts to determine sub-table sizes when building the
127 decoding tables.
128 */
129
130 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
131 for (len = 0; len <= MAXBITS; len++)
132 count[len] = 0;
133 for (sym = 0; sym < codes; sym++)
134 count[lens[sym]]++;
135
136 /* bound code lengths, force root to be within code lengths */
137 root = *bits;
138 for (max = MAXBITS; max >= 1; max--)
139 if (count[max] != 0) break;
140 if (root > max) root = max;
141 if (max == 0) { /* no symbols to code at all */
142 this.op = (unsigned char)64; /* invalid code marker */
143 this.bits = (unsigned char)1;
144 this.val = (unsigned short)0;
145 *(*table)++ = this; /* make a table to force an error */
146 *(*table)++ = this;
147 *bits = 1;
148 return 0; /* no symbols, but wait for decoding to report error */
149 }
150 for (min = 1; min <= MAXBITS; min++)
151 if (count[min] != 0) break;
152 if (root < min) root = min;
153
154 /* check for an over-subscribed or incomplete set of lengths */
155 left = 1;
156 for (len = 1; len <= MAXBITS; len++) {
157 left <<= 1;
158 left -= count[len];
159 if (left < 0) return -1; /* over-subscribed */
160 }
161 if (left > 0 && (type == CODES || max != 1))
162 return -1; /* incomplete set */
163
164 /* generate offsets into symbol table for each length for sorting */
165 offs[1] = 0;
166 for (len = 1; len < MAXBITS; len++)
167 offs[len + 1] = offs[len] + count[len];
168
169 /* sort symbols by length, by symbol order within each length */
170 for (sym = 0; sym < codes; sym++)
171 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
172
173 /*
174 Create and fill in decoding tables. In this loop, the table being
175 filled is at next and has curr index bits. The code being used is huff
176 with length len. That code is converted to an index by dropping drop
177 bits off of the bottom. For codes where len is less than drop + curr,
178 those top drop + curr - len bits are incremented through all values to
179 fill the table with replicated entries.
180
181 root is the number of index bits for the root table. When len exceeds
182 root, sub-tables are created pointed to by the root entry with an index
183 of the low root bits of huff. This is saved in low to check for when a
184 new sub-table should be started. drop is zero when the root table is
185 being filled, and drop is root when sub-tables are being filled.
186
187 When a new sub-table is needed, it is necessary to look ahead in the
188 code lengths to determine what size sub-table is needed. The length
189 counts are used for this, and so count[] is decremented as codes are
190 entered in the tables.
191
192 used keeps track of how many table entries have been allocated from the
193 provided *table space. It is checked when a LENS table is being made
194 against the space in *table, ENOUGH, minus the maximum space needed by
195 the worst case distance code, MAXD. This should never happen, but the
196 sufficiency of ENOUGH has not been proven exhaustively, hence the check.
197 This assumes that when type == LENS, bits == 9.
198
199 sym increments through all symbols, and the loop terminates when
200 all codes of length max, i.e. all codes, have been processed. This
201 routine permits incomplete codes, so another loop after this one fills
202 in the rest of the decoding tables with invalid code markers.
203 */
204
205 /* set up for code type */
206 switch (type) {
207 case CODES:
208 base = extra = work; /* dummy value--not used */
209 match = 20;
210 break;
211 case LENS:
212 base = lbase;
213 extra = lext;
214 match = 257;
215 break;
216 default: /* DISTS */
217 base = dbase;
218 extra = dext;
219 match = 0;
220 }
221
222 /* initialize state for loop */
223 huff = 0; /* starting code */
224 sym = 0; /* starting code symbol */
225 len = min; /* starting code length */
226 next = *table; /* current table to fill in */
227 curr = root; /* current table index bits */
228 drop = 0; /* current bits to drop from code for index */
229 low = (unsigned)(-1); /* trigger new sub-table when len > root */
230 used = 1U << root; /* use root table entries */
231 mask = used - 1; /* mask for comparing low */
232
233 /* check available table space */
234 if (type == LENS && used >= ENOUGH - MAXD)
235 return 1;
236
237 /* process all codes and make table entries */
238 for (;;) {
239 /* create table entry */
240 this.bits = (unsigned char)(len - drop);
241 if (work[sym] + 1 < match) {
242 this.op = (unsigned char)0;
243 this.val = work[sym];
244 }
245 else if (work[sym] >= match) {
246 this.op = (unsigned char)(extra[work[sym] - match]);
247 this.val = base[work[sym] - match];
248 }
249 else {
250 this.op = (unsigned char)(32 + 64); /* end of block */
251 this.val = 0;
252 }
253
254 /* replicate for those indices with low len bits equal to huff */
255 incr = 1U << (len - drop);
256 fill = 1U << curr;
257 min = fill; /* save offset to next table */
258 do {
259 fill -= incr;
260 next[(huff >> drop) + fill] = this;
261 } while (fill != 0);
262
263 /* backwards increment the len-bit code huff */
264 incr = 1U << (len - 1);
265 while (huff & incr)
266 incr >>= 1;
267 if (incr != 0) {
268 huff &= incr - 1;
269 huff += incr;
270 }
271 else
272 huff = 0;
273
274 /* go to next symbol, update count, len */
275 sym++;
276 if (--(count[len]) == 0) {
277 if (len == max) break;
278 len = lens[work[sym]];
279 }
280
281 /* create new sub-table if needed */
282 if (len > root && (huff & mask) != low) {
283 /* if first time, transition to sub-tables */
284 if (drop == 0)
285 drop = root;
286
287 /* increment past last table */
288 next += min; /* here min is 1 << curr */
289
290 /* determine length of next table */
291 curr = len - drop;
292 left = (int)(1 << curr);
293 while (curr + drop < max) {
294 left -= count[curr + drop];
295 if (left <= 0) break;
296 curr++;
297 left <<= 1;
298 }
299
300 /* check for enough space */
301 used += 1U << curr;
302 if (type == LENS && used >= ENOUGH - MAXD)
303 return 1;
304
305 /* point entry in root table to sub-table */
306 low = huff & mask;
307 (*table)[low].op = (unsigned char)curr;
308 (*table)[low].bits = (unsigned char)root;
309 (*table)[low].val = (unsigned short)(next - *table);
310 }
311 }
312
313 /*
314 Fill in rest of table for incomplete codes. This loop is similar to the
315 loop above in incrementing huff for table indices. It is assumed that
316 len is equal to curr + drop, so there is no loop needed to increment
317 through high index bits. When the current sub-table is filled, the loop
318 drops back to the root table to fill in any remaining entries there.
319 */
320 this.op = (unsigned char)64; /* invalid code marker */
321 this.bits = (unsigned char)(len - drop);
322 this.val = (unsigned short)0;
323 while (huff != 0) {
324 /* when done with sub-table, drop back to root table */
325 if (drop != 0 && (huff & mask) != low) {
326 drop = 0;
327 len = root;
328 next = *table;
329 this.bits = (unsigned char)len;
330 }
331
332 /* put invalid code marker in table */
333 next[huff >> drop] = this;
334
335 /* backwards increment the len-bit code huff */
336 incr = 1U << (len - 1);
337 while (huff & incr)
338 incr >>= 1;
339 if (incr != 0) {
340 huff &= incr - 1;
341 huff += incr;
342 }
343 else
344 huff = 0;
345 }
346
347 /* set return parameters */
348 *table += used;
349 *bits = root;
350 return 0;
351 }
352