1 /* inftree9.c -- generate Huffman trees for efficient decoding
2 * Copyright (C) 1995-2024 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
11 const char inflate9_copyright[] =
12 " inflate9 1.3.1 Copyright 1995-2024 Mark Adler ";
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.
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.
32 int inflate_table9(codetype type, unsigned short FAR *lens, unsigned codes,
33 code FAR * FAR *table, unsigned FAR *bits,
34 unsigned short FAR *work) {
35 unsigned len; /* a code's length in bits */
36 unsigned sym; /* index of code symbols */
37 unsigned min, max; /* minimum and maximum code lengths */
38 unsigned root; /* number of index bits for root table */
39 unsigned curr; /* number of index bits for current table */
40 unsigned drop; /* code bits to drop for sub-table */
41 int left; /* number of prefix codes available */
42 unsigned used; /* code entries in table used */
43 unsigned huff; /* Huffman code */
44 unsigned incr; /* for incrementing code, index */
45 unsigned fill; /* index for replicating entries */
46 unsigned low; /* low bits for current root entry */
47 unsigned mask; /* mask for low root bits */
48 code this; /* table entry for duplication */
49 code FAR *next; /* next available space in table */
50 const unsigned short FAR *base; /* base value table to use */
51 const unsigned short FAR *extra; /* extra bits table to use */
52 int end; /* use base and extra for symbol > end */
53 unsigned short count[MAXBITS+1]; /* number of codes of each length */
54 unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
55 static const unsigned short lbase[31] = { /* Length codes 257..285 base */
56 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17,
57 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115,
58 131, 163, 195, 227, 3, 0, 0};
59 static const unsigned short lext[31] = { /* Length codes 257..285 extra */
60 128, 128, 128, 128, 128, 128, 128, 128, 129, 129, 129, 129,
61 130, 130, 130, 130, 131, 131, 131, 131, 132, 132, 132, 132,
62 133, 133, 133, 133, 144, 203, 77};
63 static const unsigned short dbase[32] = { /* Distance codes 0..31 base */
64 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49,
65 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073,
66 4097, 6145, 8193, 12289, 16385, 24577, 32769, 49153};
67 static const unsigned short dext[32] = { /* Distance codes 0..31 extra */
68 128, 128, 128, 128, 129, 129, 130, 130, 131, 131, 132, 132,
69 133, 133, 134, 134, 135, 135, 136, 136, 137, 137, 138, 138,
70 139, 139, 140, 140, 141, 141, 142, 142};
73 Process a set of code lengths to create a canonical Huffman code. The
74 code lengths are lens[0..codes-1]. Each length corresponds to the
75 symbols 0..codes-1. The Huffman code is generated by first sorting the
76 symbols by length from short to long, and retaining the symbol order
77 for codes with equal lengths. Then the code starts with all zero bits
78 for the first code of the shortest length, and the codes are integer
79 increments for the same length, and zeros are appended as the length
80 increases. For the deflate format, these bits are stored backwards
81 from their more natural integer increment ordering, and so when the
82 decoding tables are built in the large loop below, the integer codes
83 are incremented backwards.
85 This routine assumes, but does not check, that all of the entries in
86 lens[] are in the range 0..MAXBITS. The caller must assure this.
87 1..MAXBITS is interpreted as that code length. zero means that that
88 symbol does not occur in this code.
90 The codes are sorted by computing a count of codes for each length,
91 creating from that a table of starting indices for each length in the
92 sorted table, and then entering the symbols in order in the sorted
93 table. The sorted table is work[], with that space being provided by
96 The length counts are used for other purposes as well, i.e. finding
97 the minimum and maximum length codes, determining if there are any
98 codes at all, checking for a valid set of lengths, and looking ahead
99 at length counts to determine sub-table sizes when building the
103 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
104 for (len = 0; len <= MAXBITS; len++)
106 for (sym = 0; sym < codes; sym++)
109 /* bound code lengths, force root to be within code lengths */
111 for (max = MAXBITS; max >= 1; max--)
112 if (count[max] != 0) break;
113 if (root > max) root = max;
114 if (max == 0) return -1; /* no codes! */
115 for (min = 1; min <= MAXBITS; min++)
116 if (count[min] != 0) break;
117 if (root < min) root = min;
119 /* check for an over-subscribed or incomplete set of lengths */
121 for (len = 1; len <= MAXBITS; len++) {
124 if (left < 0) return -1; /* over-subscribed */
126 if (left > 0 && (type == CODES || max != 1))
127 return -1; /* incomplete set */
129 /* generate offsets into symbol table for each length for sorting */
131 for (len = 1; len < MAXBITS; len++)
132 offs[len + 1] = offs[len] + count[len];
134 /* sort symbols by length, by symbol order within each length */
135 for (sym = 0; sym < codes; sym++)
136 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
139 Create and fill in decoding tables. In this loop, the table being
140 filled is at next and has curr index bits. The code being used is huff
141 with length len. That code is converted to an index by dropping drop
142 bits off of the bottom. For codes where len is less than drop + curr,
143 those top drop + curr - len bits are incremented through all values to
144 fill the table with replicated entries.
146 root is the number of index bits for the root table. When len exceeds
147 root, sub-tables are created pointed to by the root entry with an index
148 of the low root bits of huff. This is saved in low to check for when a
149 new sub-table should be started. drop is zero when the root table is
150 being filled, and drop is root when sub-tables are being filled.
152 When a new sub-table is needed, it is necessary to look ahead in the
153 code lengths to determine what size sub-table is needed. The length
154 counts are used for this, and so count[] is decremented as codes are
155 entered in the tables.
157 used keeps track of how many table entries have been allocated from the
158 provided *table space. It is checked for LENS and DIST tables against
159 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
160 the initial root table size constants. See the comments in inftree9.h
161 for more information.
163 sym increments through all symbols, and the loop terminates when
164 all codes of length max, i.e. all codes, have been processed. This
165 routine permits incomplete codes, so another loop after this one fills
166 in the rest of the decoding tables with invalid code markers.
169 /* set up for code type */
172 base = extra = work; /* dummy value--not used */
188 /* initialize state for loop */
189 huff = 0; /* starting code */
190 sym = 0; /* starting code symbol */
191 len = min; /* starting code length */
192 next = *table; /* current table to fill in */
193 curr = root; /* current table index bits */
194 drop = 0; /* current bits to drop from code for index */
195 low = (unsigned)(-1); /* trigger new sub-table when len > root */
196 used = 1U << root; /* use root table entries */
197 mask = used - 1; /* mask for comparing low */
199 /* check available table space */
200 if ((type == LENS && used >= ENOUGH_LENS) ||
201 (type == DISTS && used >= ENOUGH_DISTS))
204 /* process all codes and make table entries */
206 /* create table entry */
207 this.bits = (unsigned char)(len - drop);
208 if ((int)(work[sym]) < end) {
209 this.op = (unsigned char)0;
210 this.val = work[sym];
212 else if ((int)(work[sym]) > end) {
213 this.op = (unsigned char)(extra[work[sym]]);
214 this.val = base[work[sym]];
217 this.op = (unsigned char)(32 + 64); /* end of block */
221 /* replicate for those indices with low len bits equal to huff */
222 incr = 1U << (len - drop);
226 next[(huff >> drop) + fill] = this;
229 /* backwards increment the len-bit code huff */
230 incr = 1U << (len - 1);
240 /* go to next symbol, update count, len */
242 if (--(count[len]) == 0) {
243 if (len == max) break;
244 len = lens[work[sym]];
247 /* create new sub-table if needed */
248 if (len > root && (huff & mask) != low) {
249 /* if first time, transition to sub-tables */
253 /* increment past last table */
256 /* determine length of next table */
258 left = (int)(1 << curr);
259 while (curr + drop < max) {
260 left -= count[curr + drop];
261 if (left <= 0) break;
266 /* check for enough space */
268 if ((type == LENS && used >= ENOUGH_LENS) ||
269 (type == DISTS && used >= ENOUGH_DISTS))
272 /* point entry in root table to sub-table */
274 (*table)[low].op = (unsigned char)curr;
275 (*table)[low].bits = (unsigned char)root;
276 (*table)[low].val = (unsigned short)(next - *table);
281 Fill in rest of table for incomplete codes. This loop is similar to the
282 loop above in incrementing huff for table indices. It is assumed that
283 len is equal to curr + drop, so there is no loop needed to increment
284 through high index bits. When the current sub-table is filled, the loop
285 drops back to the root table to fill in any remaining entries there.
287 this.op = (unsigned char)64; /* invalid code marker */
288 this.bits = (unsigned char)(len - drop);
289 this.val = (unsigned short)0;
291 /* when done with sub-table, drop back to root table */
292 if (drop != 0 && (huff & mask) != low) {
297 this.bits = (unsigned char)len;
300 /* put invalid code marker in table */
301 next[huff >> drop] = this;
303 /* backwards increment the len-bit code huff */
304 incr = 1U << (len - 1);
315 /* set return parameters */