1 | /* inftrees.c -- generate Huffman trees for efficient decoding |
2 | * Copyright (C) 1995-2023 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 1.3 Copyright 1995-2023 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 | int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens, |
33 | unsigned codes, code FAR * FAR *table, |
34 | unsigned FAR *bits, unsigned short FAR *work) { |
35 | unsigned len; /* a code's length in bits */ |
36 | unsigned sym; /* index of code symbols */ |
37 | unsigned min, max; /* minimum and maximum code lengths */ |
38 | unsigned root; /* number of index bits for root table */ |
39 | unsigned curr; /* number of index bits for current table */ |
40 | unsigned drop; /* code bits to drop for sub-table */ |
41 | int left; /* number of prefix codes available */ |
42 | unsigned used; /* code entries in table used */ |
43 | unsigned huff; /* Huffman code */ |
44 | unsigned incr; /* for incrementing code, index */ |
45 | unsigned fill; /* index for replicating entries */ |
46 | unsigned low; /* low bits for current root entry */ |
47 | unsigned mask; /* mask for low root bits */ |
48 | code here; /* table entry for duplication */ |
49 | code FAR *next; /* next available space in table */ |
50 | const unsigned short FAR *base; /* base value table to use */ |
51 | const unsigned short FAR *; /* extra bits table to use */ |
52 | unsigned match; /* use base and extra for symbol >= match */ |
53 | unsigned short count[MAXBITS+1]; /* number of codes of each length */ |
54 | unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ |
55 | static const unsigned short lbase[31] = { /* Length codes 257..285 base */ |
56 | 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, |
57 | 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; |
58 | static const unsigned short lext[31] = { /* Length codes 257..285 extra */ |
59 | 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, |
60 | 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 198, 203}; |
61 | static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ |
62 | 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, |
63 | 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, |
64 | 8193, 12289, 16385, 24577, 0, 0}; |
65 | static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ |
66 | 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, |
67 | 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, |
68 | 28, 28, 29, 29, 64, 64}; |
69 | |
70 | /* |
71 | Process a set of code lengths to create a canonical Huffman code. The |
72 | code lengths are lens[0..codes-1]. Each length corresponds to the |
73 | symbols 0..codes-1. The Huffman code is generated by first sorting the |
74 | symbols by length from short to long, and retaining the symbol order |
75 | for codes with equal lengths. Then the code starts with all zero bits |
76 | for the first code of the shortest length, and the codes are integer |
77 | increments for the same length, and zeros are appended as the length |
78 | increases. For the deflate format, these bits are stored backwards |
79 | from their more natural integer increment ordering, and so when the |
80 | decoding tables are built in the large loop below, the integer codes |
81 | are incremented backwards. |
82 | |
83 | This routine assumes, but does not check, that all of the entries in |
84 | lens[] are in the range 0..MAXBITS. The caller must assure this. |
85 | 1..MAXBITS is interpreted as that code length. zero means that that |
86 | symbol does not occur in this code. |
87 | |
88 | The codes are sorted by computing a count of codes for each length, |
89 | creating from that a table of starting indices for each length in the |
90 | sorted table, and then entering the symbols in order in the sorted |
91 | table. The sorted table is work[], with that space being provided by |
92 | the caller. |
93 | |
94 | The length counts are used for other purposes as well, i.e. finding |
95 | the minimum and maximum length codes, determining if there are any |
96 | codes at all, checking for a valid set of lengths, and looking ahead |
97 | at length counts to determine sub-table sizes when building the |
98 | decoding tables. |
99 | */ |
100 | |
101 | /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ |
102 | for (len = 0; len <= MAXBITS; len++) |
103 | count[len] = 0; |
104 | for (sym = 0; sym < codes; sym++) |
105 | count[lens[sym]]++; |
106 | |
107 | /* bound code lengths, force root to be within code lengths */ |
108 | root = *bits; |
109 | for (max = MAXBITS; max >= 1; max--) |
110 | if (count[max] != 0) break; |
111 | if (root > max) root = max; |
112 | if (max == 0) { /* no symbols to code at all */ |
113 | here.op = (unsigned char)64; /* invalid code marker */ |
114 | here.bits = (unsigned char)1; |
115 | here.val = (unsigned short)0; |
116 | *(*table)++ = here; /* make a table to force an error */ |
117 | *(*table)++ = here; |
118 | *bits = 1; |
119 | return 0; /* no symbols, but wait for decoding to report error */ |
120 | } |
121 | for (min = 1; min < max; min++) |
122 | if (count[min] != 0) break; |
123 | if (root < min) root = min; |
124 | |
125 | /* check for an over-subscribed or incomplete set of lengths */ |
126 | left = 1; |
127 | for (len = 1; len <= MAXBITS; len++) { |
128 | left <<= 1; |
129 | left -= count[len]; |
130 | if (left < 0) return -1; /* over-subscribed */ |
131 | } |
132 | if (left > 0 && (type == CODES || max != 1)) |
133 | return -1; /* incomplete set */ |
134 | |
135 | /* generate offsets into symbol table for each length for sorting */ |
136 | offs[1] = 0; |
137 | for (len = 1; len < MAXBITS; len++) |
138 | offs[len + 1] = offs[len] + count[len]; |
139 | |
140 | /* sort symbols by length, by symbol order within each length */ |
141 | for (sym = 0; sym < codes; sym++) |
142 | if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; |
143 | |
144 | /* |
145 | Create and fill in decoding tables. In this loop, the table being |
146 | filled is at next and has curr index bits. The code being used is huff |
147 | with length len. That code is converted to an index by dropping drop |
148 | bits off of the bottom. For codes where len is less than drop + curr, |
149 | those top drop + curr - len bits are incremented through all values to |
150 | fill the table with replicated entries. |
151 | |
152 | root is the number of index bits for the root table. When len exceeds |
153 | root, sub-tables are created pointed to by the root entry with an index |
154 | of the low root bits of huff. This is saved in low to check for when a |
155 | new sub-table should be started. drop is zero when the root table is |
156 | being filled, and drop is root when sub-tables are being filled. |
157 | |
158 | When a new sub-table is needed, it is necessary to look ahead in the |
159 | code lengths to determine what size sub-table is needed. The length |
160 | counts are used for this, and so count[] is decremented as codes are |
161 | entered in the tables. |
162 | |
163 | used keeps track of how many table entries have been allocated from the |
164 | provided *table space. It is checked for LENS and DIST tables against |
165 | the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in |
166 | the initial root table size constants. See the comments in inftrees.h |
167 | for more information. |
168 | |
169 | sym increments through all symbols, and the loop terminates when |
170 | all codes of length max, i.e. all codes, have been processed. This |
171 | routine permits incomplete codes, so another loop after this one fills |
172 | in the rest of the decoding tables with invalid code markers. |
173 | */ |
174 | |
175 | /* set up for code type */ |
176 | switch (type) { |
177 | case CODES: |
178 | base = extra = work; /* dummy value--not used */ |
179 | match = 20; |
180 | break; |
181 | case LENS: |
182 | base = lbase; |
183 | extra = lext; |
184 | match = 257; |
185 | break; |
186 | default: /* DISTS */ |
187 | base = dbase; |
188 | extra = dext; |
189 | match = 0; |
190 | } |
191 | |
192 | /* initialize state for loop */ |
193 | huff = 0; /* starting code */ |
194 | sym = 0; /* starting code symbol */ |
195 | len = min; /* starting code length */ |
196 | next = *table; /* current table to fill in */ |
197 | curr = root; /* current table index bits */ |
198 | drop = 0; /* current bits to drop from code for index */ |
199 | low = (unsigned)(-1); /* trigger new sub-table when len > root */ |
200 | used = 1U << root; /* use root table entries */ |
201 | mask = used - 1; /* mask for comparing low */ |
202 | |
203 | /* check available table space */ |
204 | if ((type == LENS && used > ENOUGH_LENS) || |
205 | (type == DISTS && used > ENOUGH_DISTS)) |
206 | return 1; |
207 | |
208 | /* process all codes and make table entries */ |
209 | for (;;) { |
210 | /* create table entry */ |
211 | here.bits = (unsigned char)(len - drop); |
212 | if (work[sym] + 1U < match) { |
213 | here.op = (unsigned char)0; |
214 | here.val = work[sym]; |
215 | } |
216 | else if (work[sym] >= match) { |
217 | here.op = (unsigned char)(extra[work[sym] - match]); |
218 | here.val = base[work[sym] - match]; |
219 | } |
220 | else { |
221 | here.op = (unsigned char)(32 + 64); /* end of block */ |
222 | here.val = 0; |
223 | } |
224 | |
225 | /* replicate for those indices with low len bits equal to huff */ |
226 | incr = 1U << (len - drop); |
227 | fill = 1U << curr; |
228 | min = fill; /* save offset to next table */ |
229 | do { |
230 | fill -= incr; |
231 | next[(huff >> drop) + fill] = here; |
232 | } while (fill != 0); |
233 | |
234 | /* backwards increment the len-bit code huff */ |
235 | incr = 1U << (len - 1); |
236 | while (huff & incr) |
237 | incr >>= 1; |
238 | if (incr != 0) { |
239 | huff &= incr - 1; |
240 | huff += incr; |
241 | } |
242 | else |
243 | huff = 0; |
244 | |
245 | /* go to next symbol, update count, len */ |
246 | sym++; |
247 | if (--(count[len]) == 0) { |
248 | if (len == max) break; |
249 | len = lens[work[sym]]; |
250 | } |
251 | |
252 | /* create new sub-table if needed */ |
253 | if (len > root && (huff & mask) != low) { |
254 | /* if first time, transition to sub-tables */ |
255 | if (drop == 0) |
256 | drop = root; |
257 | |
258 | /* increment past last table */ |
259 | next += min; /* here min is 1 << curr */ |
260 | |
261 | /* determine length of next table */ |
262 | curr = len - drop; |
263 | left = (int)(1 << curr); |
264 | while (curr + drop < max) { |
265 | left -= count[curr + drop]; |
266 | if (left <= 0) break; |
267 | curr++; |
268 | left <<= 1; |
269 | } |
270 | |
271 | /* check for enough space */ |
272 | used += 1U << curr; |
273 | if ((type == LENS && used > ENOUGH_LENS) || |
274 | (type == DISTS && used > ENOUGH_DISTS)) |
275 | return 1; |
276 | |
277 | /* point entry in root table to sub-table */ |
278 | low = huff & mask; |
279 | (*table)[low].op = (unsigned char)curr; |
280 | (*table)[low].bits = (unsigned char)root; |
281 | (*table)[low].val = (unsigned short)(next - *table); |
282 | } |
283 | } |
284 | |
285 | /* fill in remaining table entry if code is incomplete (guaranteed to have |
286 | at most one remaining entry, since if the code is incomplete, the |
287 | maximum code length that was allowed to get this far is one bit) */ |
288 | if (huff != 0) { |
289 | here.op = (unsigned char)64; /* invalid code marker */ |
290 | here.bits = (unsigned char)(len - drop); |
291 | here.val = (unsigned short)0; |
292 | next[huff] = here; |
293 | } |
294 | |
295 | /* set return parameters */ |
296 | *table += used; |
297 | *bits = root; |
298 | return 0; |
299 | } |
300 | |