1 /* inftree9.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2017 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6 #include "zutil.h"
7 #include "inftree9.h"
8
9 #define MAXBITS 15
10
11 const char inflate9_copyright[] =
12 " inflate9 1.2.11 Copyright 1995-2017 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 */
inflate_table9(type,lens,codes,table,bits,work)32 int inflate_table9(type, lens, codes, table, bits, work)
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 */
53 code this; /* table entry for duplication */
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 */
57 int end; /* use base and extra for symbol > end */
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 */
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};
64 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
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, 77, 202};
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};
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;
119 if (max == 0) return -1; /* no codes! */
120 for (min = 1; min <= MAXBITS; min++)
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
165 the initial root table size constants. See the comments in inftree9.h
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 */
178 end = 19;
179 break;
180 case LENS:
181 base = lbase;
182 base -= 257;
183 extra = lext;
184 extra -= 257;
185 end = 256;
186 break;
187 default: /* DISTS */
188 base = dbase;
189 extra = dext;
190 end = -1;
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 */
205 if ((type == LENS && used >= ENOUGH_LENS) ||
206 (type == DISTS && used >= ENOUGH_DISTS))
207 return 1;
208
209 /* process all codes and make table entries */
210 for (;;) {
211 /* create table entry */
212 this.bits = (unsigned char)(len - drop);
213 if ((int)(work[sym]) < end) {
214 this.op = (unsigned char)0;
215 this.val = work[sym];
216 }
217 else if ((int)(work[sym]) > end) {
218 this.op = (unsigned char)(extra[work[sym]]);
219 this.val = base[work[sym]];
220 }
221 else {
222 this.op = (unsigned char)(32 + 64); /* end of block */
223 this.val = 0;
224 }
225
226 /* replicate for those indices with low len bits equal to huff */
227 incr = 1U << (len - drop);
228 fill = 1U << curr;
229 do {
230 fill -= incr;
231 next[(huff >> drop) + fill] = this;
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 += 1U << 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 /*
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;
318 }
319
320 /* set return parameters */
321 *table += used;
322 *bits = root;
323 return 0;
324 }
325