Mercurial > repos > blastem
comparison zlib/inftrees.c @ 1692:5dacaef602a7 segacd
Merge from default
author | Michael Pavone <pavone@retrodev.com> |
---|---|
date | Sat, 05 Jan 2019 00:58:08 -0800 |
parents | 00d788dac91a |
children |
comparison
equal
deleted
inserted
replaced
1504:95b3a1a8b26c | 1692:5dacaef602a7 |
---|---|
1 /* inftrees.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 "inftrees.h" | |
8 | |
9 #define MAXBITS 15 | |
10 | |
11 const char inflate_copyright[] = | |
12 " inflate 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 */ | |
32 int ZLIB_INTERNAL inflate_table(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 here; /* 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 unsigned match; /* use base and extra for symbol >= match */ | |
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, 19, 23, 27, 31, | |
62 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; | |
63 static const unsigned short lext[31] = { /* Length codes 257..285 extra */ | |
64 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, | |
65 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 77, 202}; | |
66 static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ | |
67 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, | |
68 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, | |
69 8193, 12289, 16385, 24577, 0, 0}; | |
70 static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ | |
71 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, | |
72 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, | |
73 28, 28, 29, 29, 64, 64}; | |
74 | |
75 /* | |
76 Process a set of code lengths to create a canonical Huffman code. The | |
77 code lengths are lens[0..codes-1]. Each length corresponds to the | |
78 symbols 0..codes-1. The Huffman code is generated by first sorting the | |
79 symbols by length from short to long, and retaining the symbol order | |
80 for codes with equal lengths. Then the code starts with all zero bits | |
81 for the first code of the shortest length, and the codes are integer | |
82 increments for the same length, and zeros are appended as the length | |
83 increases. For the deflate format, these bits are stored backwards | |
84 from their more natural integer increment ordering, and so when the | |
85 decoding tables are built in the large loop below, the integer codes | |
86 are incremented backwards. | |
87 | |
88 This routine assumes, but does not check, that all of the entries in | |
89 lens[] are in the range 0..MAXBITS. The caller must assure this. | |
90 1..MAXBITS is interpreted as that code length. zero means that that | |
91 symbol does not occur in this code. | |
92 | |
93 The codes are sorted by computing a count of codes for each length, | |
94 creating from that a table of starting indices for each length in the | |
95 sorted table, and then entering the symbols in order in the sorted | |
96 table. The sorted table is work[], with that space being provided by | |
97 the caller. | |
98 | |
99 The length counts are used for other purposes as well, i.e. finding | |
100 the minimum and maximum length codes, determining if there are any | |
101 codes at all, checking for a valid set of lengths, and looking ahead | |
102 at length counts to determine sub-table sizes when building the | |
103 decoding tables. | |
104 */ | |
105 | |
106 /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ | |
107 for (len = 0; len <= MAXBITS; len++) | |
108 count[len] = 0; | |
109 for (sym = 0; sym < codes; sym++) | |
110 count[lens[sym]]++; | |
111 | |
112 /* bound code lengths, force root to be within code lengths */ | |
113 root = *bits; | |
114 for (max = MAXBITS; max >= 1; max--) | |
115 if (count[max] != 0) break; | |
116 if (root > max) root = max; | |
117 if (max == 0) { /* no symbols to code at all */ | |
118 here.op = (unsigned char)64; /* invalid code marker */ | |
119 here.bits = (unsigned char)1; | |
120 here.val = (unsigned short)0; | |
121 *(*table)++ = here; /* make a table to force an error */ | |
122 *(*table)++ = here; | |
123 *bits = 1; | |
124 return 0; /* no symbols, but wait for decoding to report error */ | |
125 } | |
126 for (min = 1; min < max; min++) | |
127 if (count[min] != 0) break; | |
128 if (root < min) root = min; | |
129 | |
130 /* check for an over-subscribed or incomplete set of lengths */ | |
131 left = 1; | |
132 for (len = 1; len <= MAXBITS; len++) { | |
133 left <<= 1; | |
134 left -= count[len]; | |
135 if (left < 0) return -1; /* over-subscribed */ | |
136 } | |
137 if (left > 0 && (type == CODES || max != 1)) | |
138 return -1; /* incomplete set */ | |
139 | |
140 /* generate offsets into symbol table for each length for sorting */ | |
141 offs[1] = 0; | |
142 for (len = 1; len < MAXBITS; len++) | |
143 offs[len + 1] = offs[len] + count[len]; | |
144 | |
145 /* sort symbols by length, by symbol order within each length */ | |
146 for (sym = 0; sym < codes; sym++) | |
147 if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; | |
148 | |
149 /* | |
150 Create and fill in decoding tables. In this loop, the table being | |
151 filled is at next and has curr index bits. The code being used is huff | |
152 with length len. That code is converted to an index by dropping drop | |
153 bits off of the bottom. For codes where len is less than drop + curr, | |
154 those top drop + curr - len bits are incremented through all values to | |
155 fill the table with replicated entries. | |
156 | |
157 root is the number of index bits for the root table. When len exceeds | |
158 root, sub-tables are created pointed to by the root entry with an index | |
159 of the low root bits of huff. This is saved in low to check for when a | |
160 new sub-table should be started. drop is zero when the root table is | |
161 being filled, and drop is root when sub-tables are being filled. | |
162 | |
163 When a new sub-table is needed, it is necessary to look ahead in the | |
164 code lengths to determine what size sub-table is needed. The length | |
165 counts are used for this, and so count[] is decremented as codes are | |
166 entered in the tables. | |
167 | |
168 used keeps track of how many table entries have been allocated from the | |
169 provided *table space. It is checked for LENS and DIST tables against | |
170 the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in | |
171 the initial root table size constants. See the comments in inftrees.h | |
172 for more information. | |
173 | |
174 sym increments through all symbols, and the loop terminates when | |
175 all codes of length max, i.e. all codes, have been processed. This | |
176 routine permits incomplete codes, so another loop after this one fills | |
177 in the rest of the decoding tables with invalid code markers. | |
178 */ | |
179 | |
180 /* set up for code type */ | |
181 switch (type) { | |
182 case CODES: | |
183 base = extra = work; /* dummy value--not used */ | |
184 match = 20; | |
185 break; | |
186 case LENS: | |
187 base = lbase; | |
188 extra = lext; | |
189 match = 257; | |
190 break; | |
191 default: /* DISTS */ | |
192 base = dbase; | |
193 extra = dext; | |
194 match = 0; | |
195 } | |
196 | |
197 /* initialize state for loop */ | |
198 huff = 0; /* starting code */ | |
199 sym = 0; /* starting code symbol */ | |
200 len = min; /* starting code length */ | |
201 next = *table; /* current table to fill in */ | |
202 curr = root; /* current table index bits */ | |
203 drop = 0; /* current bits to drop from code for index */ | |
204 low = (unsigned)(-1); /* trigger new sub-table when len > root */ | |
205 used = 1U << root; /* use root table entries */ | |
206 mask = used - 1; /* mask for comparing low */ | |
207 | |
208 /* check available table space */ | |
209 if ((type == LENS && used > ENOUGH_LENS) || | |
210 (type == DISTS && used > ENOUGH_DISTS)) | |
211 return 1; | |
212 | |
213 /* process all codes and make table entries */ | |
214 for (;;) { | |
215 /* create table entry */ | |
216 here.bits = (unsigned char)(len - drop); | |
217 if (work[sym] + 1U < match) { | |
218 here.op = (unsigned char)0; | |
219 here.val = work[sym]; | |
220 } | |
221 else if (work[sym] >= match) { | |
222 here.op = (unsigned char)(extra[work[sym] - match]); | |
223 here.val = base[work[sym] - match]; | |
224 } | |
225 else { | |
226 here.op = (unsigned char)(32 + 64); /* end of block */ | |
227 here.val = 0; | |
228 } | |
229 | |
230 /* replicate for those indices with low len bits equal to huff */ | |
231 incr = 1U << (len - drop); | |
232 fill = 1U << curr; | |
233 min = fill; /* save offset to next table */ | |
234 do { | |
235 fill -= incr; | |
236 next[(huff >> drop) + fill] = here; | |
237 } while (fill != 0); | |
238 | |
239 /* backwards increment the len-bit code huff */ | |
240 incr = 1U << (len - 1); | |
241 while (huff & incr) | |
242 incr >>= 1; | |
243 if (incr != 0) { | |
244 huff &= incr - 1; | |
245 huff += incr; | |
246 } | |
247 else | |
248 huff = 0; | |
249 | |
250 /* go to next symbol, update count, len */ | |
251 sym++; | |
252 if (--(count[len]) == 0) { | |
253 if (len == max) break; | |
254 len = lens[work[sym]]; | |
255 } | |
256 | |
257 /* create new sub-table if needed */ | |
258 if (len > root && (huff & mask) != low) { | |
259 /* if first time, transition to sub-tables */ | |
260 if (drop == 0) | |
261 drop = root; | |
262 | |
263 /* increment past last table */ | |
264 next += min; /* here min is 1 << curr */ | |
265 | |
266 /* determine length of next table */ | |
267 curr = len - drop; | |
268 left = (int)(1 << curr); | |
269 while (curr + drop < max) { | |
270 left -= count[curr + drop]; | |
271 if (left <= 0) break; | |
272 curr++; | |
273 left <<= 1; | |
274 } | |
275 | |
276 /* check for enough space */ | |
277 used += 1U << curr; | |
278 if ((type == LENS && used > ENOUGH_LENS) || | |
279 (type == DISTS && used > ENOUGH_DISTS)) | |
280 return 1; | |
281 | |
282 /* point entry in root table to sub-table */ | |
283 low = huff & mask; | |
284 (*table)[low].op = (unsigned char)curr; | |
285 (*table)[low].bits = (unsigned char)root; | |
286 (*table)[low].val = (unsigned short)(next - *table); | |
287 } | |
288 } | |
289 | |
290 /* fill in remaining table entry if code is incomplete (guaranteed to have | |
291 at most one remaining entry, since if the code is incomplete, the | |
292 maximum code length that was allowed to get this far is one bit) */ | |
293 if (huff != 0) { | |
294 here.op = (unsigned char)64; /* invalid code marker */ | |
295 here.bits = (unsigned char)(len - drop); | |
296 here.val = (unsigned short)0; | |
297 next[huff] = here; | |
298 } | |
299 | |
300 /* set return parameters */ | |
301 *table += used; | |
302 *bits = root; | |
303 return 0; | |
304 } |