Line data Source code
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 0 : int zlib_inflate_table(codetype type, unsigned short *lens, unsigned codes,
24 : code **table, unsigned *bits, unsigned short *work)
25 : {
26 0 : unsigned len; /* a code's length in bits */
27 0 : unsigned sym; /* index of code symbols */
28 0 : unsigned min, max; /* minimum and maximum code lengths */
29 0 : unsigned root; /* number of index bits for root table */
30 0 : unsigned curr; /* number of index bits for current table */
31 0 : unsigned drop; /* code bits to drop for sub-table */
32 0 : int left; /* number of prefix codes available */
33 0 : unsigned used; /* code entries in table used */
34 0 : unsigned huff; /* Huffman code */
35 0 : unsigned incr; /* for incrementing code, index */
36 0 : unsigned fill; /* index for replicating entries */
37 0 : unsigned low; /* low bits for current root entry */
38 0 : unsigned mask; /* mask for low root bits */
39 0 : code this; /* table entry for duplication */
40 0 : code *next; /* next available space in table */
41 0 : const unsigned short *base; /* base value table to use */
42 0 : const unsigned short *extra; /* extra bits table to use */
43 0 : int end; /* use base and extra for symbol > end */
44 0 : unsigned short count[MAXBITS+1]; /* number of codes of each length */
45 0 : unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
46 0 : 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 0 : 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 0 : 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 0 : 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 0 : for (len = 0; len <= MAXBITS; len++)
94 0 : count[len] = 0;
95 0 : for (sym = 0; sym < codes; sym++)
96 0 : count[lens[sym]]++;
97 :
98 : /* bound code lengths, force root to be within code lengths */
99 0 : root = *bits;
100 0 : for (max = MAXBITS; max >= 1; max--)
101 0 : if (count[max] != 0) break;
102 0 : if (root > max) root = max;
103 0 : if (max == 0) { /* no symbols to code at all */
104 0 : this.op = (unsigned char)64; /* invalid code marker */
105 0 : this.bits = (unsigned char)1;
106 0 : this.val = (unsigned short)0;
107 0 : *(*table)++ = this; /* make a table to force an error */
108 0 : *(*table)++ = this;
109 0 : *bits = 1;
110 0 : return 0; /* no symbols, but wait for decoding to report error */
111 : }
112 0 : for (min = 1; min < MAXBITS; min++)
113 0 : if (count[min] != 0) break;
114 0 : if (root < min) root = min;
115 :
116 : /* check for an over-subscribed or incomplete set of lengths */
117 0 : left = 1;
118 0 : for (len = 1; len <= MAXBITS; len++) {
119 0 : left <<= 1;
120 0 : left -= count[len];
121 0 : if (left < 0) return -1; /* over-subscribed */
122 : }
123 0 : 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 0 : offs[1] = 0;
128 0 : for (len = 1; len < MAXBITS; len++)
129 0 : offs[len + 1] = offs[len] + count[len];
130 :
131 : /* sort symbols by length, by symbol order within each length */
132 0 : for (sym = 0; sym < codes; sym++)
133 0 : 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 0 : switch (type) {
169 : case CODES:
170 : base = extra = work; /* dummy value--not used */
171 : end = 19;
172 : break;
173 0 : case LENS:
174 0 : base = lbase;
175 0 : base -= 257;
176 0 : extra = lext;
177 0 : extra -= 257;
178 0 : end = 256;
179 0 : break;
180 0 : default: /* DISTS */
181 0 : base = dbase;
182 0 : extra = dext;
183 0 : end = -1;
184 : }
185 :
186 : /* initialize state for loop */
187 0 : huff = 0; /* starting code */
188 0 : sym = 0; /* starting code symbol */
189 0 : len = min; /* starting code length */
190 0 : next = *table; /* current table to fill in */
191 0 : curr = root; /* current table index bits */
192 0 : drop = 0; /* current bits to drop from code for index */
193 0 : low = (unsigned)(-1); /* trigger new sub-table when len > root */
194 0 : used = 1U << root; /* use root table entries */
195 0 : mask = used - 1; /* mask for comparing low */
196 :
197 : /* check available table space */
198 0 : if (type == LENS && used >= ENOUGH - MAXD)
199 : return 1;
200 :
201 : /* process all codes and make table entries */
202 0 : for (;;) {
203 : /* create table entry */
204 0 : this.bits = (unsigned char)(len - drop);
205 0 : if ((int)(work[sym]) < end) {
206 : this.op = (unsigned char)0;
207 : this.val = work[sym];
208 : }
209 0 : else if ((int)(work[sym]) > end) {
210 0 : this.op = (unsigned char)(extra[work[sym]]);
211 0 : 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 0 : incr = 1U << (len - drop);
220 0 : fill = 1U << curr;
221 0 : min = fill; /* save offset to next table */
222 0 : do {
223 0 : fill -= incr;
224 0 : next[(huff >> drop) + fill] = this;
225 0 : } while (fill != 0);
226 :
227 : /* backwards increment the len-bit code huff */
228 0 : incr = 1U << (len - 1);
229 0 : while (huff & incr)
230 0 : incr >>= 1;
231 0 : if (incr != 0) {
232 0 : huff &= incr - 1;
233 0 : huff += incr;
234 : }
235 : else
236 : huff = 0;
237 :
238 : /* go to next symbol, update count, len */
239 0 : sym++;
240 0 : if (--(count[len]) == 0) {
241 0 : if (len == max) break;
242 0 : len = lens[work[sym]];
243 : }
244 :
245 : /* create new sub-table if needed */
246 0 : if (len > root && (huff & mask) != low) {
247 : /* if first time, transition to sub-tables */
248 0 : if (drop == 0)
249 0 : drop = root;
250 :
251 : /* increment past last table */
252 0 : next += min; /* here min is 1 << curr */
253 :
254 : /* determine length of next table */
255 0 : curr = len - drop;
256 0 : left = (int)(1 << curr);
257 0 : while (curr + drop < max) {
258 0 : left -= count[curr + drop];
259 0 : if (left <= 0) break;
260 0 : curr++;
261 0 : left <<= 1;
262 : }
263 :
264 : /* check for enough space */
265 0 : used += 1U << curr;
266 0 : if (type == LENS && used >= ENOUGH - MAXD)
267 : return 1;
268 :
269 : /* point entry in root table to sub-table */
270 0 : low = huff & mask;
271 0 : (*table)[low].op = (unsigned char)curr;
272 0 : (*table)[low].bits = (unsigned char)root;
273 0 : (*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 0 : this.op = (unsigned char)64; /* invalid code marker */
285 : this.bits = (unsigned char)(len - drop);
286 0 : this.val = (unsigned short)0;
287 0 : while (huff != 0) {
288 : /* when done with sub-table, drop back to root table */
289 0 : if (drop != 0 && (huff & mask) != low) {
290 0 : drop = 0;
291 0 : len = root;
292 0 : next = *table;
293 0 : this.bits = (unsigned char)len;
294 : }
295 :
296 : /* put invalid code marker in table */
297 0 : next[huff >> drop] = this;
298 :
299 : /* backwards increment the len-bit code huff */
300 0 : incr = 1U << (len - 1);
301 0 : while (huff & incr)
302 0 : incr >>= 1;
303 0 : if (incr != 0) {
304 0 : huff &= incr - 1;
305 0 : huff += incr;
306 : }
307 : else
308 : huff = 0;
309 : }
310 :
311 : /* set return parameters */
312 0 : *table += used;
313 0 : *bits = root;
314 0 : return 0;
315 : }
|
