1 | /* |
2 | * Copyright (c) 2008-2016, 2020 Apple Inc. All rights reserved. |
3 | * |
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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 |
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 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 | |