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1 | /* inftree9.c -- generate Huffman trees for efficient decoding |
2 | * Copyright (C) 1995-2022 Mark Adler |
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3 | * For conditions of distribution and use, see copyright notice in zlib.h |
4 | */ |
5 | |
6 | #include "zutil.h" |
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7 | #include "inftree9.h" |
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8 | |
9 | #define MAXBITS 15 |
10 | |
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11 | const char inflate9_copyright[] = |
12 | " inflate9 1.2.13 Copyright 1995-2022 Mark Adler "; |
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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 | */ |
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32 | int inflate_table9(type, lens, codes, table, bits, work) |
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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 */ |
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53 | code this; /* table entry for duplication */ |
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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 */ |
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57 | int end; /* use base and extra for symbol > end */ |
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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 */ |
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61 | 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, |
62 | 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, |
63 | 131, 163, 195, 227, 3, 0, 0}; |
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64 | static const unsigned short lext[31] = { /* Length codes 257..285 extra */ |
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65 | 128, 128, 128, 128, 128, 128, 128, 128, 129, 129, 129, 129, |
66 | 130, 130, 130, 130, 131, 131, 131, 131, 132, 132, 132, 132, |
67 | 133, 133, 133, 133, 144, 194, 65}; |
68 | static const unsigned short dbase[32] = { /* Distance codes 0..31 base */ |
69 | 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, |
70 | 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, |
71 | 4097, 6145, 8193, 12289, 16385, 24577, 32769, 49153}; |
72 | static const unsigned short dext[32] = { /* Distance codes 0..31 extra */ |
73 | 128, 128, 128, 128, 129, 129, 130, 130, 131, 131, 132, 132, |
74 | 133, 133, 134, 134, 135, 135, 136, 136, 137, 137, 138, 138, |
75 | 139, 139, 140, 140, 141, 141, 142, 142}; |
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76 | |
77 | /* |
78 | Process a set of code lengths to create a canonical Huffman code. The |
79 | code lengths are lens[0..codes-1]. Each length corresponds to the |
80 | symbols 0..codes-1. The Huffman code is generated by first sorting the |
81 | symbols by length from short to long, and retaining the symbol order |
82 | for codes with equal lengths. Then the code starts with all zero bits |
83 | for the first code of the shortest length, and the codes are integer |
84 | increments for the same length, and zeros are appended as the length |
85 | increases. For the deflate format, these bits are stored backwards |
86 | from their more natural integer increment ordering, and so when the |
87 | decoding tables are built in the large loop below, the integer codes |
88 | are incremented backwards. |
89 | |
90 | This routine assumes, but does not check, that all of the entries in |
91 | lens[] are in the range 0..MAXBITS. The caller must assure this. |
92 | 1..MAXBITS is interpreted as that code length. zero means that that |
93 | symbol does not occur in this code. |
94 | |
95 | The codes are sorted by computing a count of codes for each length, |
96 | creating from that a table of starting indices for each length in the |
97 | sorted table, and then entering the symbols in order in the sorted |
98 | table. The sorted table is work[], with that space being provided by |
99 | the caller. |
100 | |
101 | The length counts are used for other purposes as well, i.e. finding |
102 | the minimum and maximum length codes, determining if there are any |
103 | codes at all, checking for a valid set of lengths, and looking ahead |
104 | at length counts to determine sub-table sizes when building the |
105 | decoding tables. |
106 | */ |
107 | |
108 | /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ |
109 | for (len = 0; len <= MAXBITS; len++) |
110 | count[len] = 0; |
111 | for (sym = 0; sym < codes; sym++) |
112 | count[lens[sym]]++; |
113 | |
114 | /* bound code lengths, force root to be within code lengths */ |
115 | root = *bits; |
116 | for (max = MAXBITS; max >= 1; max--) |
117 | if (count[max] != 0) break; |
118 | if (root > max) root = max; |
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119 | if (max == 0) return -1; /* no codes! */ |
120 | for (min = 1; min <= MAXBITS; min++) |
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121 | if (count[min] != 0) break; |
122 | if (root < min) root = min; |
123 | |
124 | /* check for an over-subscribed or incomplete set of lengths */ |
125 | left = 1; |
126 | for (len = 1; len <= MAXBITS; len++) { |
127 | left <<= 1; |
128 | left -= count[len]; |
129 | if (left < 0) return -1; /* over-subscribed */ |
130 | } |
131 | if (left > 0 && (type == CODES || max != 1)) |
132 | return -1; /* incomplete set */ |
133 | |
134 | /* generate offsets into symbol table for each length for sorting */ |
135 | offs[1] = 0; |
136 | for (len = 1; len < MAXBITS; len++) |
137 | offs[len + 1] = offs[len] + count[len]; |
138 | |
139 | /* sort symbols by length, by symbol order within each length */ |
140 | for (sym = 0; sym < codes; sym++) |
141 | if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; |
142 | |
143 | /* |
144 | Create and fill in decoding tables. In this loop, the table being |
145 | filled is at next and has curr index bits. The code being used is huff |
146 | with length len. That code is converted to an index by dropping drop |
147 | bits off of the bottom. For codes where len is less than drop + curr, |
148 | those top drop + curr - len bits are incremented through all values to |
149 | fill the table with replicated entries. |
150 | |
151 | root is the number of index bits for the root table. When len exceeds |
152 | root, sub-tables are created pointed to by the root entry with an index |
153 | of the low root bits of huff. This is saved in low to check for when a |
154 | new sub-table should be started. drop is zero when the root table is |
155 | being filled, and drop is root when sub-tables are being filled. |
156 | |
157 | When a new sub-table is needed, it is necessary to look ahead in the |
158 | code lengths to determine what size sub-table is needed. The length |
159 | counts are used for this, and so count[] is decremented as codes are |
160 | entered in the tables. |
161 | |
162 | used keeps track of how many table entries have been allocated from the |
163 | provided *table space. It is checked for LENS and DIST tables against |
164 | the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in |
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165 | the initial root table size constants. See the comments in inftree9.h |
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166 | for more information. |
167 | |
168 | sym increments through all symbols, and the loop terminates when |
169 | all codes of length max, i.e. all codes, have been processed. This |
170 | routine permits incomplete codes, so another loop after this one fills |
171 | in the rest of the decoding tables with invalid code markers. |
172 | */ |
173 | |
174 | /* set up for code type */ |
175 | switch (type) { |
176 | case CODES: |
177 | base = extra = work; /* dummy value--not used */ |
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178 | end = 19; |
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179 | break; |
180 | case LENS: |
181 | base = lbase; |
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182 | base -= 257; |
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183 | extra = lext; |
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184 | extra -= 257; |
185 | end = 256; |
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186 | break; |
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187 | default: /* DISTS */ |
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188 | base = dbase; |
189 | extra = dext; |
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190 | end = -1; |
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191 | } |
192 | |
193 | /* initialize state for loop */ |
194 | huff = 0; /* starting code */ |
195 | sym = 0; /* starting code symbol */ |
196 | len = min; /* starting code length */ |
197 | next = *table; /* current table to fill in */ |
198 | curr = root; /* current table index bits */ |
199 | drop = 0; /* current bits to drop from code for index */ |
200 | low = (unsigned)(-1); /* trigger new sub-table when len > root */ |
201 | used = 1U << root; /* use root table entries */ |
202 | mask = used - 1; /* mask for comparing low */ |
203 | |
204 | /* check available table space */ |
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205 | if ((type == LENS && used >= ENOUGH_LENS) || |
206 | (type == DISTS && used >= ENOUGH_DISTS)) |
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207 | return 1; |
208 | |
209 | /* process all codes and make table entries */ |
210 | for (;;) { |
211 | /* create table entry */ |
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212 | this.bits = (unsigned char)(len - drop); |
213 | if ((int)(work[sym]) < end) { |
214 | this.op = (unsigned char)0; |
215 | this.val = work[sym]; |
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216 | } |
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217 | else if ((int)(work[sym]) > end) { |
218 | this.op = (unsigned char)(extra[work[sym]]); |
219 | this.val = base[work[sym]]; |
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220 | } |
221 | else { |
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222 | this.op = (unsigned char)(32 + 64); /* end of block */ |
223 | this.val = 0; |
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224 | } |
225 | |
226 | /* replicate for those indices with low len bits equal to huff */ |
227 | incr = 1U << (len - drop); |
228 | fill = 1U << curr; |
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229 | do { |
230 | fill -= incr; |
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231 | next[(huff >> drop) + fill] = this; |
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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 */ |
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259 | next += 1U << curr; |
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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; |
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273 | if ((type == LENS && used >= ENOUGH_LENS) || |
274 | (type == DISTS && used >= ENOUGH_DISTS)) |
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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 | |
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285 | /* |
286 | Fill in rest of table for incomplete codes. This loop is similar to the |
287 | loop above in incrementing huff for table indices. It is assumed that |
288 | len is equal to curr + drop, so there is no loop needed to increment |
289 | through high index bits. When the current sub-table is filled, the loop |
290 | drops back to the root table to fill in any remaining entries there. |
291 | */ |
292 | this.op = (unsigned char)64; /* invalid code marker */ |
293 | this.bits = (unsigned char)(len - drop); |
294 | this.val = (unsigned short)0; |
295 | while (huff != 0) { |
296 | /* when done with sub-table, drop back to root table */ |
297 | if (drop != 0 && (huff & mask) != low) { |
298 | drop = 0; |
299 | len = root; |
300 | next = *table; |
301 | curr = root; |
302 | this.bits = (unsigned char)len; |
303 | } |
304 | |
305 | /* put invalid code marker in table */ |
306 | next[huff >> drop] = this; |
307 | |
308 | /* backwards increment the len-bit code huff */ |
309 | incr = 1U << (len - 1); |
310 | while (huff & incr) |
311 | incr >>= 1; |
312 | if (incr != 0) { |
313 | huff &= incr - 1; |
314 | huff += incr; |
315 | } |
316 | else |
317 | huff = 0; |
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318 | } |
319 | |
320 | /* set return parameters */ |
321 | *table += used; |
322 | *bits = root; |
323 | return 0; |
324 | } |