1 /* inftrees.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2003 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
14 const char inflate_copyright[] =
15 " inflate 1.2.1 Copyright 1995-2003 Mark Adler ";
17 If you use the zlib library in a product, an acknowledgment is welcome
18 in the documentation of your product. If for some reason you cannot
19 include such an acknowledgment, I would appreciate that you keep this
20 copyright string in the executable of your product.
24 Build a set of tables to decode the provided canonical Huffman code.
25 The code lengths are lens[0..codes-1]. The result starts at *table,
26 whose indices are 0..2^bits-1. work is a writable array of at least
27 lens shorts, which is used as a work area. type is the type of code
28 to be generated, CODES, LENS, or DISTS. On return, zero is success,
29 -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
30 on return points to the next available entry's address. bits is the
31 requested root table index bits, and on return it is the actual root
32 table index bits. It will differ if the request is greater than the
33 longest code or if it is less than the shortest code.
35 int inflate_table(type, lens, codes, table, bits, work)
37 unsigned short FAR *lens;
39 code FAR * FAR *table;
41 unsigned short FAR *work;
43 unsigned len; /* a code's length in bits */
44 unsigned sym; /* index of code symbols */
45 unsigned min, max; /* minimum and maximum code lengths */
46 unsigned root; /* number of index bits for root table */
47 unsigned curr; /* number of index bits for current table */
48 unsigned drop; /* code bits to drop for sub-table */
49 int left; /* number of prefix codes available */
50 unsigned used; /* code entries in table used */
51 unsigned huff; /* Huffman code */
52 unsigned incr; /* for incrementing code, index */
53 unsigned fill; /* index for replicating entries */
54 unsigned low; /* low bits for current root entry */
55 unsigned mask; /* mask for low root bits */
56 code this; /* table entry for duplication */
57 code FAR *next; /* next available space in table */
58 const unsigned short FAR *base; /* base value table to use */
59 const unsigned short FAR *extra; /* extra bits table to use */
60 int end; /* use base and extra for symbol > end */
61 unsigned short count[MAXBITS+1]; /* number of codes of each length */
62 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
63 static const unsigned short lbase[31] = { /* Length codes 257..285 base */
64 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
65 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
66 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
67 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
68 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 76, 66};
69 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
70 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
71 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
72 8193, 12289, 16385, 24577, 0, 0};
73 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
74 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
75 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
76 28, 28, 29, 29, 64, 64};
79 Process a set of code lengths to create a canonical Huffman code. The
80 code lengths are lens[0..codes-1]. Each length corresponds to the
81 symbols 0..codes-1. The Huffman code is generated by first sorting the
82 symbols by length from short to long, and retaining the symbol order
83 for codes with equal lengths. Then the code starts with all zero bits
84 for the first code of the shortest length, and the codes are integer
85 increments for the same length, and zeros are appended as the length
86 increases. For the deflate format, these bits are stored backwards
87 from their more natural integer increment ordering, and so when the
88 decoding tables are built in the large loop below, the integer codes
89 are incremented backwards.
91 This routine assumes, but does not check, that all of the entries in
92 lens[] are in the range 0..MAXBITS. The caller must assure this.
93 1..MAXBITS is interpreted as that code length. zero means that that
94 symbol does not occur in this code.
96 The codes are sorted by computing a count of codes for each length,
97 creating from that a table of starting indices for each length in the
98 sorted table, and then entering the symbols in order in the sorted
99 table. The sorted table is work[], with that space being provided by
102 The length counts are used for other purposes as well, i.e. finding
103 the minimum and maximum length codes, determining if there are any
104 codes at all, checking for a valid set of lengths, and looking ahead
105 at length counts to determine sub-table sizes when building the
109 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
110 for (len = 0; len <= MAXBITS; len++)
112 for (sym = 0; sym < codes; sym++)
115 /* bound code lengths, force root to be within code lengths */
117 for (max = MAXBITS; max >= 1; max--)
118 if (count[max] != 0) break;
119 if (root > max) root = max;
120 if (max == 0) return -1; /* no codes! */
121 for (min = 1; min <= MAXBITS; min++)
122 if (count[min] != 0) break;
123 if (root < min) root = min;
125 /* check for an over-subscribed or incomplete set of lengths */
127 for (len = 1; len <= MAXBITS; len++) {
130 if (left < 0) return -1; /* over-subscribed */
132 if (left > 0 && (type == CODES || (codes - count[0] != 1)))
133 return -1; /* incomplete set */
135 /* generate offsets into symbol table for each length for sorting */
137 for (len = 1; len < MAXBITS; len++)
138 offs[len + 1] = offs[len] + count[len];
140 /* sort symbols by length, by symbol order within each length */
141 for (sym = 0; sym < codes; sym++)
142 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
145 Create and fill in decoding tables. In this loop, the table being
146 filled is at next and has curr index bits. The code being used is huff
147 with length len. That code is converted to an index by dropping drop
148 bits off of the bottom. For codes where len is less than drop + curr,
149 those top drop + curr - len bits are incremented through all values to
150 fill the table with replicated entries.
152 root is the number of index bits for the root table. When len exceeds
153 root, sub-tables are created pointed to by the root entry with an index
154 of the low root bits of huff. This is saved in low to check for when a
155 new sub-table should be started. drop is zero when the root table is
156 being filled, and drop is root when sub-tables are being filled.
158 When a new sub-table is needed, it is necessary to look ahead in the
159 code lengths to determine what size sub-table is needed. The length
160 counts are used for this, and so count[] is decremented as codes are
161 entered in the tables.
163 used keeps track of how many table entries have been allocated from the
164 provided *table space. It is checked when a LENS table is being made
165 against the space in *table, ENOUGH, minus the maximum space needed by
166 the worst case distance code, MAXD. This should never happen, but the
167 sufficiency of ENOUGH has not been proven exhaustively, hence the check.
168 This assumes that when type == LENS, bits == 9.
170 sym increments through all symbols, and the loop terminates when
171 all codes of length max, i.e. all codes, have been processed. This
172 routine permits incomplete codes, so another loop after this one fills
173 in the rest of the decoding tables with invalid code markers.
176 /* set up for code type */
179 base = extra = work; /* dummy value--not used */
195 /* initialize state for loop */
196 huff = 0; /* starting code */
197 sym = 0; /* starting code symbol */
198 len = min; /* starting code length */
199 next = *table; /* current table to fill in */
200 curr = root; /* current table index bits */
201 drop = 0; /* current bits to drop from code for index */
202 low = (unsigned)(-1); /* trigger new sub-table when len > root */
203 used = 1U << root; /* use root table entries */
204 mask = used - 1; /* mask for comparing low */
206 /* check available table space */
207 if (type == LENS && used >= ENOUGH - MAXD)
210 /* process all codes and make table entries */
212 /* create table entry */
213 this.bits = (unsigned char)(len - drop);
214 if ((int)(work[sym]) < end) {
215 this.op = (unsigned char)0;
216 this.val = work[sym];
218 else if ((int)(work[sym]) > end) {
219 this.op = (unsigned char)(extra[work[sym]]);
220 this.val = base[work[sym]];
223 this.op = (unsigned char)(32 + 64); /* end of block */
227 /* replicate for those indices with low len bits equal to huff */
228 incr = 1U << (len - drop);
232 next[(huff >> drop) + fill] = this;
235 /* backwards increment the len-bit code huff */
236 incr = 1U << (len - 1);
246 /* go to next symbol, update count, len */
248 if (--(count[len]) == 0) {
249 if (len == max) break;
250 len = lens[work[sym]];
253 /* create new sub-table if needed */
254 if (len > root && (huff & mask) != low) {
255 /* if first time, transition to sub-tables */
259 /* increment past last table */
262 /* determine length of next table */
264 left = (int)(1 << curr);
265 while (curr + drop < max) {
266 left -= count[curr + drop];
267 if (left <= 0) break;
272 /* check for enough space */
274 if (type == LENS && used >= ENOUGH - MAXD)
277 /* point entry in root table to sub-table */
279 (*table)[low].op = (unsigned char)curr;
280 (*table)[low].bits = (unsigned char)root;
281 (*table)[low].val = (unsigned short)(next - *table);
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.
292 this.op = (unsigned char)64; /* invalid code marker */
293 this.bits = (unsigned char)(len - drop);
294 this.val = (unsigned short)0;
296 /* when done with sub-table, drop back to root table */
297 if (drop != 0 && (huff & mask) != low) {
302 this.bits = (unsigned char)len;
305 /* put invalid code marker in table */
306 next[huff >> drop] = this;
308 /* backwards increment the len-bit code huff */
309 incr = 1U << (len - 1);
320 /* set return parameters */