1 /* inftrees.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2013 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 zRCSID("$MirOS: src/kern/z/inftrees.c,v 1.4 2013/08/05 21:27:34 tg Exp $")
10
11 #define MAXBITS 15
12
13 #ifndef SMALL
14 const char inflate_copyright[] =
15 " inflate 1.2.8 Copyright 1995-2013 Mark Adler ";
16 #endif
17 /*
18 If you use the zlib library in a product, an acknowledgment is welcome
19 in the documentation of your product. If for some reason you cannot
20 include such an acknowledgment, I would appreciate that you keep this
21 copyright string in the executable of your product.
22 */
23
24 /*
25 Build a set of tables to decode the provided canonical Huffman code.
26 The code lengths are lens[0..codes-1]. The result starts at *table,
27 whose indices are 0..2^bits-1. work is a writable array of at least
28 lens shorts, which is used as a work area. type is the type of code
29 to be generated, CODES, LENS, or DISTS. On return, zero is success,
30 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
31 on return points to the next available entry's address. bits is the
32 requested root table index bits, and on return it is the actual root
33 table index bits. It will differ if the request is greater than the
34 longest code or if it is less than the shortest code.
35 */
inflate_table(type,lens,codes,table,bits,work)36 int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work)
37 codetype type;
38 unsigned short FAR *lens;
39 unsigned codes;
40 code FAR * FAR *table;
41 unsigned FAR *bits;
42 unsigned short FAR *work;
43 {
44 unsigned len; /* a code's length in bits */
45 unsigned sym; /* index of code symbols */
46 unsigned min, max; /* minimum and maximum code lengths */
47 unsigned root; /* number of index bits for root table */
48 unsigned curr; /* number of index bits for current table */
49 unsigned drop; /* code bits to drop for sub-table */
50 int left; /* number of prefix codes available */
51 unsigned used; /* code entries in table used */
52 unsigned huff; /* Huffman code */
53 unsigned incr; /* for incrementing code, index */
54 unsigned fill; /* index for replicating entries */
55 unsigned low; /* low bits for current root entry */
56 unsigned mask; /* mask for low root bits */
57 code here; /* table entry for duplication */
58 code FAR *next; /* next available space in table */
59 const unsigned short FAR *base; /* base value table to use */
60 const unsigned short FAR *extra; /* extra bits table to use */
61 int end; /* use base and extra for symbol > end */
62 unsigned short count[MAXBITS+1]; /* number of codes of each length */
63 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
64 static const unsigned short lbase[31] = { /* Length codes 257..285 base */
65 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
66 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
67 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
68 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
69 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 72, 78};
70 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
71 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
72 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
73 8193, 12289, 16385, 24577, 0, 0};
74 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
75 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
76 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
77 28, 28, 29, 29, 64, 64};
78
79 /*
80 Process a set of code lengths to create a canonical Huffman code. The
81 code lengths are lens[0..codes-1]. Each length corresponds to the
82 symbols 0..codes-1. The Huffman code is generated by first sorting the
83 symbols by length from short to long, and retaining the symbol order
84 for codes with equal lengths. Then the code starts with all zero bits
85 for the first code of the shortest length, and the codes are integer
86 increments for the same length, and zeros are appended as the length
87 increases. For the deflate format, these bits are stored backwards
88 from their more natural integer increment ordering, and so when the
89 decoding tables are built in the large loop below, the integer codes
90 are incremented backwards.
91
92 This routine assumes, but does not check, that all of the entries in
93 lens[] are in the range 0..MAXBITS. The caller must assure this.
94 1..MAXBITS is interpreted as that code length. zero means that that
95 symbol does not occur in this code.
96
97 The codes are sorted by computing a count of codes for each length,
98 creating from that a table of starting indices for each length in the
99 sorted table, and then entering the symbols in order in the sorted
100 table. The sorted table is work[], with that space being provided by
101 the caller.
102
103 The length counts are used for other purposes as well, i.e. finding
104 the minimum and maximum length codes, determining if there are any
105 codes at all, checking for a valid set of lengths, and looking ahead
106 at length counts to determine sub-table sizes when building the
107 decoding tables.
108 */
109
110 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
111 for (len = 0; len <= MAXBITS; len++)
112 count[len] = 0;
113 for (sym = 0; sym < codes; sym++)
114 count[lens[sym]]++;
115
116 /* bound code lengths, force root to be within code lengths */
117 root = *bits;
118 for (max = MAXBITS; max >= 1; max--)
119 if (count[max] != 0) break;
120 if (root > max) root = max;
121 if (max == 0) { /* no symbols to code at all */
122 here.op = (unsigned char)64; /* invalid code marker */
123 here.bits = (unsigned char)1;
124 here.val = (unsigned short)0;
125 *(*table)++ = here; /* make a table to force an error */
126 *(*table)++ = here;
127 *bits = 1;
128 return 0; /* no symbols, but wait for decoding to report error */
129 }
130 for (min = 1; min < max; min++)
131 if (count[min] != 0) break;
132 if (root < min) root = min;
133
134 /* check for an over-subscribed or incomplete set of lengths */
135 left = 1;
136 for (len = 1; len <= MAXBITS; len++) {
137 left <<= 1;
138 left -= count[len];
139 if (left < 0) return -1; /* over-subscribed */
140 }
141 if (left > 0 && (type == CODES || max != 1))
142 return -1; /* incomplete set */
143
144 /* generate offsets into symbol table for each length for sorting */
145 offs[1] = 0;
146 for (len = 1; len < MAXBITS; len++)
147 offs[len + 1] = offs[len] + count[len];
148
149 /* sort symbols by length, by symbol order within each length */
150 for (sym = 0; sym < codes; sym++)
151 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
152
153 /*
154 Create and fill in decoding tables. In this loop, the table being
155 filled is at next and has curr index bits. The code being used is huff
156 with length len. That code is converted to an index by dropping drop
157 bits off of the bottom. For codes where len is less than drop + curr,
158 those top drop + curr - len bits are incremented through all values to
159 fill the table with replicated entries.
160
161 root is the number of index bits for the root table. When len exceeds
162 root, sub-tables are created pointed to by the root entry with an index
163 of the low root bits of huff. This is saved in low to check for when a
164 new sub-table should be started. drop is zero when the root table is
165 being filled, and drop is root when sub-tables are being filled.
166
167 When a new sub-table is needed, it is necessary to look ahead in the
168 code lengths to determine what size sub-table is needed. The length
169 counts are used for this, and so count[] is decremented as codes are
170 entered in the tables.
171
172 used keeps track of how many table entries have been allocated from the
173 provided *table space. It is checked for LENS and DIST tables against
174 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
175 the initial root table size constants. See the comments in inftrees.h
176 for more information.
177
178 sym increments through all symbols, and the loop terminates when
179 all codes of length max, i.e. all codes, have been processed. This
180 routine permits incomplete codes, so another loop after this one fills
181 in the rest of the decoding tables with invalid code markers.
182 */
183
184 /* set up for code type */
185 switch (type) {
186 case CODES:
187 base = extra = work; /* dummy value--not used */
188 end = 19;
189 break;
190 case LENS:
191 base = lbase;
192 base -= 257;
193 extra = lext;
194 extra -= 257;
195 end = 256;
196 break;
197 default: /* DISTS */
198 base = dbase;
199 extra = dext;
200 end = -1;
201 }
202
203 /* initialize state for loop */
204 huff = 0; /* starting code */
205 sym = 0; /* starting code symbol */
206 len = min; /* starting code length */
207 next = *table; /* current table to fill in */
208 curr = root; /* current table index bits */
209 drop = 0; /* current bits to drop from code for index */
210 low = (unsigned)(-1); /* trigger new sub-table when len > root */
211 used = 1U << root; /* use root table entries */
212 mask = used - 1; /* mask for comparing low */
213
214 /* check available table space */
215 if ((type == LENS && used > ENOUGH_LENS) ||
216 (type == DISTS && used > ENOUGH_DISTS))
217 return 1;
218
219 /* process all codes and make table entries */
220 for (;;) {
221 /* create table entry */
222 here.bits = (unsigned char)(len - drop);
223 if ((int)(work[sym]) < end) {
224 here.op = (unsigned char)0;
225 here.val = work[sym];
226 }
227 else if ((int)(work[sym]) > end) {
228 here.op = (unsigned char)(extra[work[sym]]);
229 here.val = base[work[sym]];
230 }
231 else {
232 here.op = (unsigned char)(32 + 64); /* end of block */
233 here.val = 0;
234 }
235
236 /* replicate for those indices with low len bits equal to huff */
237 incr = 1U << (len - drop);
238 fill = 1U << curr;
239 min = fill; /* save offset to next table */
240 do {
241 fill -= incr;
242 next[(huff >> drop) + fill] = here;
243 } while (fill != 0);
244
245 /* backwards increment the len-bit code huff */
246 incr = 1U << (len - 1);
247 while (huff & incr)
248 incr >>= 1;
249 if (incr != 0) {
250 huff &= incr - 1;
251 huff += incr;
252 }
253 else
254 huff = 0;
255
256 /* go to next symbol, update count, len */
257 sym++;
258 if (--(count[len]) == 0) {
259 if (len == max) break;
260 len = lens[work[sym]];
261 }
262
263 /* create new sub-table if needed */
264 if (len > root && (huff & mask) != low) {
265 /* if first time, transition to sub-tables */
266 if (drop == 0)
267 drop = root;
268
269 /* increment past last table */
270 next += min; /* here min is 1 << curr */
271
272 /* determine length of next table */
273 curr = len - drop;
274 left = (int)(1 << curr);
275 while (curr + drop < max) {
276 left -= count[curr + drop];
277 if (left <= 0) break;
278 curr++;
279 left <<= 1;
280 }
281
282 /* check for enough space */
283 used += 1U << curr;
284 if ((type == LENS && used > ENOUGH_LENS) ||
285 (type == DISTS && used > ENOUGH_DISTS))
286 return 1;
287
288 /* point entry in root table to sub-table */
289 low = huff & mask;
290 (*table)[low].op = (unsigned char)curr;
291 (*table)[low].bits = (unsigned char)root;
292 (*table)[low].val = (unsigned short)(next - *table);
293 }
294 }
295
296 /* fill in remaining table entry if code is incomplete (guaranteed to have
297 at most one remaining entry, since if the code is incomplete, the
298 maximum code length that was allowed to get this far is one bit) */
299 if (huff != 0) {
300 here.op = (unsigned char)64; /* invalid code marker */
301 here.bits = (unsigned char)(len - drop);
302 here.val = (unsigned short)0;
303 next[huff] = here;
304 }
305
306 /* set return parameters */
307 *table += used;
308 *bits = root;
309 return 0;
310 }
311