  varnishcache/lib/libvgz/inftrees.c 
0 

/* inftrees.c  generate Huffman trees for efficient decoding 
1 

* Copyright (C) 19952023 Mark Adler 
2 

* For conditions of distribution and use, see copyright notice in zlib.h 
3 

*/ 
4 


5 

#include "zutil.h" 
6 

#include "inftrees.h" 
7 


8 

#define MAXBITS 15 
9 


10 

extern const char inflate_copyright[]; 
11 

const char inflate_copyright[] = 
12 

" inflate 1.3 Copyright 19952023 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..codes1]. The result starts at *table, 
23 

whose indices are 0..2^bits1. 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 
312 
int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens, 
33 

unsigned codes, code FAR * FAR *table, 
34 

unsigned FAR *bits, 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 subtable */ 
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 here; /* 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 

unsigned match; /* use base and extra for symbol >= match */ 
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, 19, 23, 27, 31, 
57 

35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; 
58 

static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 
59 

16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 
60 

19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 198, 203}; 
61 

static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ 
62 

1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 
63 

257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 
64 

8193, 12289, 16385, 24577, 0, 0}; 
65 

static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ 
66 

16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 
67 

23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 
68 

28, 28, 29, 29, 64, 64}; 
69 


70 

/* 
71 

Process a set of code lengths to create a canonical Huffman code. The 
72 

code lengths are lens[0..codes1]. Each length corresponds to the 
73 

symbols 0..codes1. The Huffman code is generated by first sorting the 
74 

symbols by length from short to long, and retaining the symbol order 
75 

for codes with equal lengths. Then the code starts with all zero bits 
76 

for the first code of the shortest length, and the codes are integer 
77 

increments for the same length, and zeros are appended as the length 
78 

increases. For the deflate format, these bits are stored backwards 
79 

from their more natural integer increment ordering, and so when the 
80 

decoding tables are built in the large loop below, the integer codes 
81 

are incremented backwards. 
82 


83 

This routine assumes, but does not check, that all of the entries in 
84 

lens[] are in the range 0..MAXBITS. The caller must assure this. 
85 

1..MAXBITS is interpreted as that code length. zero means that that 
86 

symbol does not occur in this code. 
87 


88 

The codes are sorted by computing a count of codes for each length, 
89 

creating from that a table of starting indices for each length in the 
90 

sorted table, and then entering the symbols in order in the sorted 
91 

table. The sorted table is work[], with that space being provided by 
92 

the caller. 
93 


94 

The length counts are used for other purposes as well, i.e. finding 
95 

the minimum and maximum length codes, determining if there are any 
96 

codes at all, checking for a valid set of lengths, and looking ahead 
97 

at length counts to determine subtable sizes when building the 
98 

decoding tables. 
99 

*/ 
100 


101 

/* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 
102 
5304 
for (len = 0; len <= MAXBITS; len++) 
103 
4992 
count[len] = 0; 
104 
31863 
for (sym = 0; sym < codes; sym++) 
105 
31551 
count[lens[sym]]++; 
106 


107 

/* bound code lengths, force root to be within code lengths */ 
108 
312 
root = *bits; 
109 
3224 
for (max = MAXBITS; max >= 1; max) 
110 
3224 
if (count[max] != 0) break; 
111 
312 
if (root > max) root = max; 
112 
312 
if (max == 0) { /* no symbols to code at all */ 
113 
0 
here.op = (unsigned char)64; /* invalid code marker */ 
114 
0 
here.bits = (unsigned char)1; 
115 
0 
here.val = (unsigned short)0; 
116 
0 
*(*table)++ = here; /* make a table to force an error */ 
117 
0 
*(*table)++ = here; 
118 
0 
*bits = 1; 
119 
0 
return 0; /* no symbols, but wait for decoding to report error */ 
120 

} 
121 
689 
for (min = 1; min < max; min++) 
122 
676 
if (count[min] != 0) break; 
123 
312 
if (root < min) root = min; 
124 


125 

/* check for an oversubscribed or incomplete set of lengths */ 
126 
312 
left = 1; 
127 
4992 
for (len = 1; len <= MAXBITS; len++) { 
128 
4680 
left <<= 1; 
129 
4680 
left = count[len]; 
130 
4680 
if (left < 0) return 1; /* oversubscribed */ 
131 
4680 
} 
132 
312 
if (left > 0 && (type == CODES  max != 1)) 
133 
0 
return 1; /* incomplete set */ 
134 


135 

/* generate offsets into symbol table for each length for sorting */ 
136 
312 
offs[1] = 0; 
137 
4680 
for (len = 1; len < MAXBITS; len++) 
138 
4368 
offs[len + 1] = offs[len] + count[len]; 
139 


140 

/* sort symbols by length, by symbol order within each length */ 
141 
31863 
for (sym = 0; sym < codes; sym++) 
142 
31551 
if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 
143 


144 

/* 
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. 
151 


152 

root is the number of index bits for the root table. When len exceeds 
153 

root, subtables 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 subtable should be started. drop is zero when the root table is 
156 

being filled, and drop is root when subtables are being filled. 
157 


158 

When a new subtable is needed, it is necessary to look ahead in the 
159 

code lengths to determine what size subtable is needed. The length 
160 

counts are used for this, and so count[] is decremented as codes are 
161 

entered in the tables. 
162 


163 

used keeps track of how many table entries have been allocated from the 
164 

provided *table space. It is checked for LENS and DIST tables against 
165 

the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 
166 

the initial root table size constants. See the comments in inftrees.h 
167 

for more information. 
168 


169 

sym increments through all symbols, and the loop terminates when 
170 

all codes of length max, i.e. all codes, have been processed. This 
171 

routine permits incomplete codes, so another loop after this one fills 
172 

in the rest of the decoding tables with invalid code markers. 
173 

*/ 
174 


175 

/* set up for code type */ 
176 
312 
switch (type) { 
177 

case CODES: 
178 
104 
base = extra = work; /* dummy valuenot used */ 
179 
104 
match = 20; 
180 
104 
break; 
181 

case LENS: 
182 
104 
base = lbase; 
183 
104 
extra = lext; 
184 
104 
match = 257; 
185 
104 
break; 
186 

default: /* DISTS */ 
187 
104 
base = dbase; 
188 
104 
extra = dext; 
189 
104 
match = 0; 
190 
104 
} 
191 


192 

/* initialize state for loop */ 
193 
312 
huff = 0; /* starting code */ 
194 
312 
sym = 0; /* starting code symbol */ 
195 
312 
len = min; /* starting code length */ 
196 
312 
next = *table; /* current table to fill in */ 
197 
312 
curr = root; /* current table index bits */ 
198 
312 
drop = 0; /* current bits to drop from code for index */ 
199 
312 
low = (unsigned)(1); /* trigger new subtable when len > root */ 
200 
312 
used = 1U << root; /* use root table entries */ 
201 
312 
mask = used  1; /* mask for comparing low */ 
202 


203 

/* check available table space */ 
204 
416 
if ((type == LENS && used > ENOUGH_LENS)  
205 
416 
(type == DISTS && used > ENOUGH_DISTS)) 
206 
208 
return 1; 
207 


208 

/* process all codes and make table entries */ 
209 
7007 
for (;;) { 
210 

/* create table entry */ 
211 
7007 
here.bits = (unsigned char)(len  drop); 
212 
7007 
if (work[sym] + 1U < match) { 
213 
5200 
here.op = (unsigned char)0; 
214 
5200 
here.val = work[sym]; 
215 
5200 
} 
216 
1807 
else if (work[sym] >= match) { 
217 
1703 
here.op = (unsigned char)(extra[work[sym]  match]); 
218 
1703 
here.val = base[work[sym]  match]; 
219 
1703 
} 
220 

else { 
221 
104 
here.op = (unsigned char)(32 + 64); /* end of block */ 
222 
104 
here.val = 0; 
223 

} 
224 


225 

/* replicate for those indices with low len bits equal to huff */ 
226 
7007 
incr = 1U << (len  drop); 
227 
7007 
fill = 1U << curr; 
228 
7007 
min = fill; /* save offset to next table */ 
229 
7007 
do { 
230 
29718 
fill = incr; 
231 
29718 
next[(huff >> drop) + fill] = here; 
232 
29718 
} while (fill != 0); 
233 


234 

/* backwards increment the lenbit code huff */ 
235 
7007 
incr = 1U << (len  1); 
236 
13702 
while (huff & incr) 
237 
6695 
incr >>= 1; 
238 
7007 
if (incr != 0) { 
239 
6695 
huff &= incr  1; 
240 
6695 
huff += incr; 
241 
6695 
} 
242 

else 
243 
312 
huff = 0; 
244 


245 

/* go to next symbol, update count, len */ 
246 
7007 
sym++; 
247 
7007 
if ((count[len]) == 0) { 
248 
1326 
if (len == max) break; 
249 
1014 
len = lens[work[sym]]; 
250 
1014 
} 
251 


252 

/* create new subtable if needed */ 
253 
6695 
if (len > root && (huff & mask) != low) { 
254 

/* if first time, transition to subtables */ 
255 
0 
if (drop == 0) 
256 
0 
drop = root; 
257 


258 

/* increment past last table */ 
259 
0 
next += min; /* here min is 1 << curr */ 
260 


261 

/* determine length of next table */ 
262 
0 
curr = len  drop; 
263 
0 
left = (int)(1 << curr); 
264 
0 
while (curr + drop < max) { 
265 
0 
left = count[curr + drop]; 
266 
0 
if (left <= 0) break; 
267 
0 
curr++; 
268 
0 
left <<= 1; 
269 

} 
270 


271 

/* check for enough space */ 
272 
0 
used += 1U << curr; 
273 
0 
if ((type == LENS && used > ENOUGH_LENS)  
274 
0 
(type == DISTS && used > ENOUGH_DISTS)) 
275 
0 
return 1; 
276 


277 

/* point entry in root table to subtable */ 
278 
0 
low = huff & mask; 
279 
0 
(*table)[low].op = (unsigned char)curr; 
280 
0 
(*table)[low].bits = (unsigned char)root; 
281 
0 
(*table)[low].val = (unsigned short)(next  *table); 
282 
0 
} 
283 

} 
284 


285 

/* fill in remaining table entry if code is incomplete (guaranteed to have 
286 

at most one remaining entry, since if the code is incomplete, the 
287 

maximum code length that was allowed to get this far is one bit) */ 
288 
312 
if (huff != 0) { 
289 
0 
here.op = (unsigned char)64; /* invalid code marker */ 
290 
0 
here.bits = (unsigned char)(len  drop); 
291 
0 
here.val = (unsigned short)0; 
292 
0 
next[huff] = here; 
293 
0 
} 
294 


295 

/* set return parameters */ 
296 
312 
*table += used; 
297 
312 
*bits = root; 
298 
312 
return 0; 
299 
520 
} 