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