1/* inftrees.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2016 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6#include "zbuild.h"
7#include "zutil.h"
8#include "inftrees.h"
9
10#define MAXBITS 15
11
12const char PREFIX(inflate_copyright)[] = " inflate 1.2.11.f Copyright 1995-2016 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 */
32int Z_INTERNAL zng_inflate_table(codetype type, uint16_t *lens, unsigned codes,
33 code * *table, unsigned *bits, uint16_t *work) {
34 unsigned len; /* a code's length in bits */
35 unsigned sym; /* index of code symbols */
36 unsigned min, max; /* minimum and maximum code lengths */
37 unsigned root; /* number of index bits for root table */
38 unsigned curr; /* number of index bits for current table */
39 unsigned drop; /* code bits to drop for sub-table */
40 int left; /* number of prefix codes available */
41 unsigned used; /* code entries in table used */
42 unsigned huff; /* Huffman code */
43 unsigned incr; /* for incrementing code, index */
44 unsigned fill; /* index for replicating entries */
45 unsigned low; /* low bits for current root entry */
46 unsigned mask; /* mask for low root bits */
47 code here; /* table entry for duplication */
48 code *next; /* next available space in table */
49 const uint16_t *base; /* base value table to use */
50 const uint16_t *extra; /* extra bits table to use */
51 unsigned match; /* use base and extra for symbol >= match */
52 uint16_t count[MAXBITS+1]; /* number of codes of each length */
53 uint16_t offs[MAXBITS+1]; /* offsets in table for each length */
54 static const uint16_t lbase[31] = { /* Length codes 257..285 base */
55 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
56 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
57 static const uint16_t lext[31] = { /* Length codes 257..285 extra */
58 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
59 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 77, 202};
60 static const uint16_t dbase[32] = { /* Distance codes 0..29 base */
61 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
62 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
63 8193, 12289, 16385, 24577, 0, 0};
64 static const uint16_t dext[32] = { /* Distance codes 0..29 extra */
65 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
66 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
67 28, 28, 29, 29, 64, 64};
68
69 /*
70 Process a set of code lengths to create a canonical Huffman code. The
71 code lengths are lens[0..codes-1]. Each length corresponds to the
72 symbols 0..codes-1. The Huffman code is generated by first sorting the
73 symbols by length from short to long, and retaining the symbol order
74 for codes with equal lengths. Then the code starts with all zero bits
75 for the first code of the shortest length, and the codes are integer
76 increments for the same length, and zeros are appended as the length
77 increases. For the deflate format, these bits are stored backwards
78 from their more natural integer increment ordering, and so when the
79 decoding tables are built in the large loop below, the integer codes
80 are incremented backwards.
81
82 This routine assumes, but does not check, that all of the entries in
83 lens[] are in the range 0..MAXBITS. The caller must assure this.
84 1..MAXBITS is interpreted as that code length. zero means that that
85 symbol does not occur in this code.
86
87 The codes are sorted by computing a count of codes for each length,
88 creating from that a table of starting indices for each length in the
89 sorted table, and then entering the symbols in order in the sorted
90 table. The sorted table is work[], with that space being provided by
91 the caller.
92
93 The length counts are used for other purposes as well, i.e. finding
94 the minimum and maximum length codes, determining if there are any
95 codes at all, checking for a valid set of lengths, and looking ahead
96 at length counts to determine sub-table sizes when building the
97 decoding tables.
98 */
99
100 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
101 for (len = 0; len <= MAXBITS; len++)
102 count[len] = 0;
103 for (sym = 0; sym < codes; sym++)
104 count[lens[sym]]++;
105
106 /* bound code lengths, force root to be within code lengths */
107 root = *bits;
108 for (max = MAXBITS; max >= 1; max--)
109 if (count[max] != 0) break;
110 if (root > max) root = max;
111 if (max == 0) { /* no symbols to code at all */
112 here.op = (unsigned char)64; /* invalid code marker */
113 here.bits = (unsigned char)1;
114 here.val = (uint16_t)0;
115 *(*table)++ = here; /* make a table to force an error */
116 *(*table)++ = here;
117 *bits = 1;
118 return 0; /* no symbols, but wait for decoding to report error */
119 }
120 for (min = 1; min < max; 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]]++] = (uint16_t)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 inftrees.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 match = 20;
179 break;
180 case LENS:
181 base = lbase;
182 extra = lext;
183 match = 257;
184 break;
185 default: /* DISTS */
186 base = dbase;
187 extra = dext;
188 match = 0;
189 }
190
191 /* initialize state for loop */
192 huff = 0; /* starting code */
193 sym = 0; /* starting code symbol */
194 len = min; /* starting code length */
195 next = *table; /* current table to fill in */
196 curr = root; /* current table index bits */
197 drop = 0; /* current bits to drop from code for index */
198 low = (unsigned)(-1); /* trigger new sub-table when len > root */
199 used = 1U << root; /* use root table entries */
200 mask = used - 1; /* mask for comparing low */
201
202 /* check available table space */
203 if ((type == LENS && used > ENOUGH_LENS) ||
204 (type == DISTS && used > ENOUGH_DISTS))
205 return 1;
206
207 /* process all codes and make table entries */
208 for (;;) {
209 /* create table entry */
210 here.bits = (unsigned char)(len - drop);
211 if (work[sym] + 1U < match) {
212 here.op = (unsigned char)0;
213 here.val = work[sym];
214 } else if (work[sym] >= match) {
215 here.op = (unsigned char)(extra[work[sym] - match]);
216 here.val = base[work[sym] - match];
217 } else {
218 here.op = (unsigned char)(32 + 64); /* end of block */
219 here.val = 0;
220 }
221
222 /* replicate for those indices with low len bits equal to huff */
223 incr = 1U << (len - drop);
224 fill = 1U << curr;
225 min = fill; /* save offset to next table */
226 do {
227 fill -= incr;
228 next[(huff >> drop) + fill] = here;
229 } while (fill != 0);
230
231 /* backwards increment the len-bit code huff */
232 incr = 1U << (len - 1);
233 while (huff & incr)
234 incr >>= 1;
235 if (incr != 0) {
236 huff &= incr - 1;
237 huff += incr;
238 } else {
239 huff = 0;
240 }
241
242 /* go to next symbol, update count, len */
243 sym++;
244 if (--(count[len]) == 0) {
245 if (len == max)
246 break;
247 len = lens[work[sym]];
248 }
249
250 /* create new sub-table if needed */
251 if (len > root && (huff & mask) != low) {
252 /* if first time, transition to sub-tables */
253 if (drop == 0)
254 drop = root;
255
256 /* increment past last table */
257 next += min; /* here min is 1 << curr */
258
259 /* determine length of next table */
260 curr = len - drop;
261 left = (int)(1 << curr);
262 while (curr + drop < max) {
263 left -= count[curr + drop];
264 if (left <= 0)
265 break;
266 curr++;
267 left <<= 1;
268 }
269
270 /* check for enough space */
271 used += 1U << curr;
272 if ((type == LENS && used > ENOUGH_LENS) || (type == DISTS && used > ENOUGH_DISTS))
273 return 1;
274
275 /* point entry in root table to sub-table */
276 low = huff & mask;
277 (*table)[low].op = (unsigned char)curr;
278 (*table)[low].bits = (unsigned char)root;
279 (*table)[low].val = (uint16_t)(next - *table);
280 }
281 }
282
283 /* fill in remaining table entry if code is incomplete (guaranteed to have
284 at most one remaining entry, since if the code is incomplete, the
285 maximum code length that was allowed to get this far is one bit) */
286 if (huff != 0) {
287 here.op = (unsigned char)64; /* invalid code marker */
288 here.bits = (unsigned char)(len - drop);
289 here.val = (uint16_t)0;
290 next[huff] = here;
291 }
292
293 /* set return parameters */
294 *table += used;
295 *bits = root;
296 return 0;
297}
298