1 | /* inftrees.c -- generate Huffman trees for efficient decoding |
2 | * Copyright (C) 1995-2005 Mark Adler |
3 | * For conditions of distribution and use, see copyright notice in zlib.h |
4 | */ |
5 | |
6 | #include <linux/zutil.h> |
7 | #include "inftrees.h" |
8 | |
9 | #define MAXBITS 15 |
10 | |
11 | /* |
12 | Build a set of tables to decode the provided canonical Huffman code. |
13 | The code lengths are lens[0..codes-1]. The result starts at *table, |
14 | whose indices are 0..2^bits-1. work is a writable array of at least |
15 | lens shorts, which is used as a work area. type is the type of code |
16 | to be generated, CODES, LENS, or DISTS. On return, zero is success, |
17 | -1 is an invalid code, and +1 means that ENOUGH isn't enough. table |
18 | on return points to the next available entry's address. bits is the |
19 | requested root table index bits, and on return it is the actual root |
20 | table index bits. It will differ if the request is greater than the |
21 | longest code or if it is less than the shortest code. |
22 | */ |
23 | int zlib_inflate_table(codetype type, unsigned short *lens, unsigned codes, |
24 | code **table, unsigned *bits, unsigned short *work) |
25 | { |
26 | unsigned len; /* a code's length in bits */ |
27 | unsigned sym; /* index of code symbols */ |
28 | unsigned min, max; /* minimum and maximum code lengths */ |
29 | unsigned root; /* number of index bits for root table */ |
30 | unsigned curr; /* number of index bits for current table */ |
31 | unsigned drop; /* code bits to drop for sub-table */ |
32 | int left; /* number of prefix codes available */ |
33 | unsigned used; /* code entries in table used */ |
34 | unsigned huff; /* Huffman code */ |
35 | unsigned incr; /* for incrementing code, index */ |
36 | unsigned fill; /* index for replicating entries */ |
37 | unsigned low; /* low bits for current root entry */ |
38 | unsigned mask; /* mask for low root bits */ |
39 | code this; /* table entry for duplication */ |
40 | code *next; /* next available space in table */ |
41 | const unsigned short *base; /* base value table to use */ |
42 | const unsigned short *; /* extra bits table to use */ |
43 | int end; /* use base and extra for symbol > end */ |
44 | unsigned short count[MAXBITS+1]; /* number of codes of each length */ |
45 | unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ |
46 | static const unsigned short lbase[31] = { /* Length codes 257..285 base */ |
47 | 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, |
48 | 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; |
49 | static const unsigned short lext[31] = { /* Length codes 257..285 extra */ |
50 | 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, |
51 | 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196}; |
52 | static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ |
53 | 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, |
54 | 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, |
55 | 8193, 12289, 16385, 24577, 0, 0}; |
56 | static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ |
57 | 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, |
58 | 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, |
59 | 28, 28, 29, 29, 64, 64}; |
60 | |
61 | /* |
62 | Process a set of code lengths to create a canonical Huffman code. The |
63 | code lengths are lens[0..codes-1]. Each length corresponds to the |
64 | symbols 0..codes-1. The Huffman code is generated by first sorting the |
65 | symbols by length from short to long, and retaining the symbol order |
66 | for codes with equal lengths. Then the code starts with all zero bits |
67 | for the first code of the shortest length, and the codes are integer |
68 | increments for the same length, and zeros are appended as the length |
69 | increases. For the deflate format, these bits are stored backwards |
70 | from their more natural integer increment ordering, and so when the |
71 | decoding tables are built in the large loop below, the integer codes |
72 | are incremented backwards. |
73 | |
74 | This routine assumes, but does not check, that all of the entries in |
75 | lens[] are in the range 0..MAXBITS. The caller must assure this. |
76 | 1..MAXBITS is interpreted as that code length. zero means that that |
77 | symbol does not occur in this code. |
78 | |
79 | The codes are sorted by computing a count of codes for each length, |
80 | creating from that a table of starting indices for each length in the |
81 | sorted table, and then entering the symbols in order in the sorted |
82 | table. The sorted table is work[], with that space being provided by |
83 | the caller. |
84 | |
85 | The length counts are used for other purposes as well, i.e. finding |
86 | the minimum and maximum length codes, determining if there are any |
87 | codes at all, checking for a valid set of lengths, and looking ahead |
88 | at length counts to determine sub-table sizes when building the |
89 | decoding tables. |
90 | */ |
91 | |
92 | /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ |
93 | for (len = 0; len <= MAXBITS; len++) |
94 | count[len] = 0; |
95 | for (sym = 0; sym < codes; sym++) |
96 | count[lens[sym]]++; |
97 | |
98 | /* bound code lengths, force root to be within code lengths */ |
99 | root = *bits; |
100 | for (max = MAXBITS; max >= 1; max--) |
101 | if (count[max] != 0) break; |
102 | if (root > max) root = max; |
103 | if (max == 0) { /* no symbols to code at all */ |
104 | this.op = (unsigned char)64; /* invalid code marker */ |
105 | this.bits = (unsigned char)1; |
106 | this.val = (unsigned short)0; |
107 | *(*table)++ = this; /* make a table to force an error */ |
108 | *(*table)++ = this; |
109 | *bits = 1; |
110 | return 0; /* no symbols, but wait for decoding to report error */ |
111 | } |
112 | for (min = 1; min < MAXBITS; min++) |
113 | if (count[min] != 0) break; |
114 | if (root < min) root = min; |
115 | |
116 | /* check for an over-subscribed or incomplete set of lengths */ |
117 | left = 1; |
118 | for (len = 1; len <= MAXBITS; len++) { |
119 | left <<= 1; |
120 | left -= count[len]; |
121 | if (left < 0) return -1; /* over-subscribed */ |
122 | } |
123 | if (left > 0 && (type == CODES || max != 1)) |
124 | return -1; /* incomplete set */ |
125 | |
126 | /* generate offsets into symbol table for each length for sorting */ |
127 | offs[1] = 0; |
128 | for (len = 1; len < MAXBITS; len++) |
129 | offs[len + 1] = offs[len] + count[len]; |
130 | |
131 | /* sort symbols by length, by symbol order within each length */ |
132 | for (sym = 0; sym < codes; sym++) |
133 | if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; |
134 | |
135 | /* |
136 | Create and fill in decoding tables. In this loop, the table being |
137 | filled is at next and has curr index bits. The code being used is huff |
138 | with length len. That code is converted to an index by dropping drop |
139 | bits off of the bottom. For codes where len is less than drop + curr, |
140 | those top drop + curr - len bits are incremented through all values to |
141 | fill the table with replicated entries. |
142 | |
143 | root is the number of index bits for the root table. When len exceeds |
144 | root, sub-tables are created pointed to by the root entry with an index |
145 | of the low root bits of huff. This is saved in low to check for when a |
146 | new sub-table should be started. drop is zero when the root table is |
147 | being filled, and drop is root when sub-tables are being filled. |
148 | |
149 | When a new sub-table is needed, it is necessary to look ahead in the |
150 | code lengths to determine what size sub-table is needed. The length |
151 | counts are used for this, and so count[] is decremented as codes are |
152 | entered in the tables. |
153 | |
154 | used keeps track of how many table entries have been allocated from the |
155 | provided *table space. It is checked when a LENS table is being made |
156 | against the space in *table, ENOUGH, minus the maximum space needed by |
157 | the worst case distance code, MAXD. This should never happen, but the |
158 | sufficiency of ENOUGH has not been proven exhaustively, hence the check. |
159 | This assumes that when type == LENS, bits == 9. |
160 | |
161 | sym increments through all symbols, and the loop terminates when |
162 | all codes of length max, i.e. all codes, have been processed. This |
163 | routine permits incomplete codes, so another loop after this one fills |
164 | in the rest of the decoding tables with invalid code markers. |
165 | */ |
166 | |
167 | /* set up for code type */ |
168 | switch (type) { |
169 | case CODES: |
170 | base = extra = work; /* dummy value--not used */ |
171 | end = 19; |
172 | break; |
173 | case LENS: |
174 | base = lbase; |
175 | base -= 257; |
176 | extra = lext; |
177 | extra -= 257; |
178 | end = 256; |
179 | break; |
180 | default: /* DISTS */ |
181 | base = dbase; |
182 | extra = dext; |
183 | end = -1; |
184 | } |
185 | |
186 | /* initialize state for loop */ |
187 | huff = 0; /* starting code */ |
188 | sym = 0; /* starting code symbol */ |
189 | len = min; /* starting code length */ |
190 | next = *table; /* current table to fill in */ |
191 | curr = root; /* current table index bits */ |
192 | drop = 0; /* current bits to drop from code for index */ |
193 | low = (unsigned)(-1); /* trigger new sub-table when len > root */ |
194 | used = 1U << root; /* use root table entries */ |
195 | mask = used - 1; /* mask for comparing low */ |
196 | |
197 | /* check available table space */ |
198 | if (type == LENS && used >= ENOUGH - MAXD) |
199 | return 1; |
200 | |
201 | /* process all codes and make table entries */ |
202 | for (;;) { |
203 | /* create table entry */ |
204 | this.bits = (unsigned char)(len - drop); |
205 | if ((int)(work[sym]) < end) { |
206 | this.op = (unsigned char)0; |
207 | this.val = work[sym]; |
208 | } |
209 | else if ((int)(work[sym]) > end) { |
210 | this.op = (unsigned char)(extra[work[sym]]); |
211 | this.val = base[work[sym]]; |
212 | } |
213 | else { |
214 | this.op = (unsigned char)(32 + 64); /* end of block */ |
215 | this.val = 0; |
216 | } |
217 | |
218 | /* replicate for those indices with low len bits equal to huff */ |
219 | incr = 1U << (len - drop); |
220 | fill = 1U << curr; |
221 | min = fill; /* save offset to next table */ |
222 | do { |
223 | fill -= incr; |
224 | next[(huff >> drop) + fill] = this; |
225 | } while (fill != 0); |
226 | |
227 | /* backwards increment the len-bit code huff */ |
228 | incr = 1U << (len - 1); |
229 | while (huff & incr) |
230 | incr >>= 1; |
231 | if (incr != 0) { |
232 | huff &= incr - 1; |
233 | huff += incr; |
234 | } |
235 | else |
236 | huff = 0; |
237 | |
238 | /* go to next symbol, update count, len */ |
239 | sym++; |
240 | if (--(count[len]) == 0) { |
241 | if (len == max) break; |
242 | len = lens[work[sym]]; |
243 | } |
244 | |
245 | /* create new sub-table if needed */ |
246 | if (len > root && (huff & mask) != low) { |
247 | /* if first time, transition to sub-tables */ |
248 | if (drop == 0) |
249 | drop = root; |
250 | |
251 | /* increment past last table */ |
252 | next += min; /* here min is 1 << curr */ |
253 | |
254 | /* determine length of next table */ |
255 | curr = len - drop; |
256 | left = (int)(1 << curr); |
257 | while (curr + drop < max) { |
258 | left -= count[curr + drop]; |
259 | if (left <= 0) break; |
260 | curr++; |
261 | left <<= 1; |
262 | } |
263 | |
264 | /* check for enough space */ |
265 | used += 1U << curr; |
266 | if (type == LENS && used >= ENOUGH - MAXD) |
267 | return 1; |
268 | |
269 | /* point entry in root table to sub-table */ |
270 | low = huff & mask; |
271 | (*table)[low].op = (unsigned char)curr; |
272 | (*table)[low].bits = (unsigned char)root; |
273 | (*table)[low].val = (unsigned short)(next - *table); |
274 | } |
275 | } |
276 | |
277 | /* |
278 | Fill in rest of table for incomplete codes. This loop is similar to the |
279 | loop above in incrementing huff for table indices. It is assumed that |
280 | len is equal to curr + drop, so there is no loop needed to increment |
281 | through high index bits. When the current sub-table is filled, the loop |
282 | drops back to the root table to fill in any remaining entries there. |
283 | */ |
284 | this.op = (unsigned char)64; /* invalid code marker */ |
285 | this.bits = (unsigned char)(len - drop); |
286 | this.val = (unsigned short)0; |
287 | while (huff != 0) { |
288 | /* when done with sub-table, drop back to root table */ |
289 | if (drop != 0 && (huff & mask) != low) { |
290 | drop = 0; |
291 | len = root; |
292 | next = *table; |
293 | this.bits = (unsigned char)len; |
294 | } |
295 | |
296 | /* put invalid code marker in table */ |
297 | next[huff >> drop] = this; |
298 | |
299 | /* backwards increment the len-bit code huff */ |
300 | incr = 1U << (len - 1); |
301 | while (huff & incr) |
302 | incr >>= 1; |
303 | if (incr != 0) { |
304 | huff &= incr - 1; |
305 | huff += incr; |
306 | } |
307 | else |
308 | huff = 0; |
309 | } |
310 | |
311 | /* set return parameters */ |
312 | *table += used; |
313 | *bits = root; |
314 | return 0; |
315 | } |
316 | |