  varnishcache/lib/libvgz/inftrees.c 
1 

/* inftrees.c  generate Huffman trees for efficient decoding 
2 

* Copyright (C) 19952017 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 

extern const char inflate_copyright[]; 
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const char inflate_copyright[] = 
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" inflate 1.2.11 Copyright 19952017 Mark Adler "; 
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/* 
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If you use the zlib library in a product, an acknowledgment is welcome 
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in the documentation of your product. If for some reason you cannot 
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include such an acknowledgment, I would appreciate that you keep this 
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copyright string in the executable of your product. 
19 

*/ 
20 


21 

/* 
22 

Build a set of tables to decode the provided canonical Huffman code. 
23 

The code lengths are lens[0..codes1]. The result starts at *table, 
24 

whose indices are 0..2^bits1. work is a writable array of at least 
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lens shorts, which is used as a work area. type is the type of code 
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to be generated, CODES, LENS, or DISTS. On return, zero is success, 
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1 is an invalid code, and +1 means that ENOUGH isn't enough. table 
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on return points to the next available entry's address. bits is the 
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requested root table index bits, and on return it is the actual root 
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table index bits. It will differ if the request is greater than the 
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longest code or if it is less than the shortest code. 
32 

*/ 
33 
63 
int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work) 
34 

codetype type; 
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unsigned short FAR *lens; 
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unsigned codes; 
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code FAR * FAR *table; 
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unsigned FAR *bits; 
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unsigned short FAR *work; 
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{ 
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unsigned len; /* a code's length in bits */ 
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unsigned sym; /* index of code symbols */ 
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unsigned min, max; /* minimum and maximum code lengths */ 
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unsigned root; /* number of index bits for root table */ 
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unsigned curr; /* number of index bits for current table */ 
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unsigned drop; /* code bits to drop for subtable */ 
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int left; /* number of prefix codes available */ 
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unsigned used; /* code entries in table used */ 
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unsigned huff; /* Huffman code */ 
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unsigned incr; /* for incrementing code, index */ 
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unsigned fill; /* index for replicating entries */ 
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unsigned low; /* low bits for current root entry */ 
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unsigned mask; /* mask for low root bits */ 
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code here; /* table entry for duplication */ 
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code FAR *next; /* next available space in table */ 
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const unsigned short FAR *base; /* base value table to use */ 
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const unsigned short FAR *extra; /* extra bits table to use */ 
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unsigned match; /* use base and extra for symbol >= match */ 
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unsigned short count[MAXBITS+1]; /* number of codes of each length */ 
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unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ 
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static const unsigned short lbase[31] = { /* Length codes 257..285 base */ 
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3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 
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35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0}; 
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static const unsigned short lext[31] = { /* Length codes 257..285 extra */ 
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16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 
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19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 77, 202}; 
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static const unsigned short dbase[32] = { /* Distance codes 0..29 base */ 
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1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 
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257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 
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8193, 12289, 16385, 24577, 0, 0}; 
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static const unsigned short dext[32] = { /* Distance codes 0..29 extra */ 
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16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 
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23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 
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28, 28, 29, 29, 64, 64}; 
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76 

/* 
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Process a set of code lengths to create a canonical Huffman code. The 
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code lengths are lens[0..codes1]. Each length corresponds to the 
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symbols 0..codes1. The Huffman code is generated by first sorting the 
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symbols by length from short to long, and retaining the symbol order 
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for codes with equal lengths. Then the code starts with all zero bits 
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for the first code of the shortest length, and the codes are integer 
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increments for the same length, and zeros are appended as the length 
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increases. For the deflate format, these bits are stored backwards 
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from their more natural integer increment ordering, and so when the 
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decoding tables are built in the large loop below, the integer codes 
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are incremented backwards. 
88 


89 

This routine assumes, but does not check, that all of the entries in 
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lens[] are in the range 0..MAXBITS. The caller must assure this. 
91 

1..MAXBITS is interpreted as that code length. zero means that that 
92 

symbol does not occur in this code. 
93 


94 

The codes are sorted by computing a count of codes for each length, 
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creating from that a table of starting indices for each length in the 
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sorted table, and then entering the symbols in order in the sorted 
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table. The sorted table is work[], with that space being provided by 
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the caller. 
99 


100 

The length counts are used for other purposes as well, i.e. finding 
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the minimum and maximum length codes, determining if there are any 
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codes at all, checking for a valid set of lengths, and looking ahead 
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at length counts to determine subtable sizes when building the 
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decoding tables. 
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*/ 
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107 

/* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ 
108 
1071 
for (len = 0; len <= MAXBITS; len++) 
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1008 
count[len] = 0; 
110 
6420 
for (sym = 0; sym < codes; sym++) 
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6357 
count[lens[sym]]++; 
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113 

/* bound code lengths, force root to be within code lengths */ 
114 
63 
root = *bits; 
115 
642 
for (max = MAXBITS; max >= 1; max) 
116 
642 
if (count[max] != 0) break; 
117 
63 
if (root > max) root = max; 
118 
63 
if (max == 0) { /* no symbols to code at all */ 
119 
0 
here.op = (unsigned char)64; /* invalid code marker */ 
120 
0 
here.bits = (unsigned char)1; 
121 
0 
here.val = (unsigned short)0; 
122 
0 
*(*table)++ = here; /* make a table to force an error */ 
123 
0 
*(*table)++ = here; 
124 
0 
*bits = 1; 
125 
0 
return 0; /* no symbols, but wait for decoding to report error */ 
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} 
127 
144 
for (min = 1; min < max; min++) 
128 
144 
if (count[min] != 0) break; 
129 
63 
if (root < min) root = min; 
130 


131 

/* check for an oversubscribed or incomplete set of lengths */ 
132 
63 
left = 1; 
133 
1008 
for (len = 1; len <= MAXBITS; len++) { 
134 
945 
left <<= 1; 
135 
945 
left = count[len]; 
136 
945 
if (left < 0) return 1; /* oversubscribed */ 
137 

} 
138 
63 
if (left > 0 && (type == CODES  max != 1)) 
139 
0 
return 1; /* incomplete set */ 
140 


141 

/* generate offsets into symbol table for each length for sorting */ 
142 
63 
offs[1] = 0; 
143 
945 
for (len = 1; len < MAXBITS; len++) 
144 
882 
offs[len + 1] = offs[len] + count[len]; 
145 


146 

/* sort symbols by length, by symbol order within each length */ 
147 
6420 
for (sym = 0; sym < codes; sym++) 
148 
6357 
if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; 
149 


150 

/* 
151 

Create and fill in decoding tables. In this loop, the table being 
152 

filled is at next and has curr index bits. The code being used is huff 
153 

with length len. That code is converted to an index by dropping drop 
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bits off of the bottom. For codes where len is less than drop + curr, 
155 

those top drop + curr  len bits are incremented through all values to 
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fill the table with replicated entries. 
157 


158 

root is the number of index bits for the root table. When len exceeds 
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root, subtables are created pointed to by the root entry with an index 
160 

of the low root bits of huff. This is saved in low to check for when a 
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new subtable should be started. drop is zero when the root table is 
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being filled, and drop is root when subtables are being filled. 
163 


164 

When a new subtable is needed, it is necessary to look ahead in the 
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code lengths to determine what size subtable is needed. The length 
166 

counts are used for this, and so count[] is decremented as codes are 
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entered in the tables. 
168 


169 

used keeps track of how many table entries have been allocated from the 
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provided *table space. It is checked for LENS and DIST tables against 
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the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 
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the initial root table size constants. See the comments in inftrees.h 
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for more information. 
174 


175 

sym increments through all symbols, and the loop terminates when 
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all codes of length max, i.e. all codes, have been processed. This 
177 

routine permits incomplete codes, so another loop after this one fills 
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in the rest of the decoding tables with invalid code markers. 
179 

*/ 
180 


181 

/* set up for code type */ 
182 
63 
switch (type) { 
183 

case CODES: 
184 
21 
base = extra = work; /* dummy valuenot used */ 
185 
21 
match = 20; 
186 
21 
break; 
187 

case LENS: 
188 
21 
base = lbase; 
189 
21 
extra = lext; 
190 
21 
match = 257; 
191 
21 
break; 
192 

default: /* DISTS */ 
193 
21 
base = dbase; 
194 
21 
extra = dext; 
195 
21 
match = 0; 
196 

} 
197 


198 

/* initialize state for loop */ 
199 
63 
huff = 0; /* starting code */ 
200 
63 
sym = 0; /* starting code symbol */ 
201 
63 
len = min; /* starting code length */ 
202 
63 
next = *table; /* current table to fill in */ 
203 
63 
curr = root; /* current table index bits */ 
204 
63 
drop = 0; /* current bits to drop from code for index */ 
205 
63 
low = (unsigned)(1); /* trigger new subtable when len > root */ 
206 
63 
used = 1U << root; /* use root table entries */ 
207 
63 
mask = used  1; /* mask for comparing low */ 
208 


209 

/* check available table space */ 
210 
63 
if ((type == LENS && used > ENOUGH_LENS)  
211 
21 
(type == DISTS && used > ENOUGH_DISTS)) 
212 
0 
return 1; 
213 


214 

/* process all codes and make table entries */ 
215 

for (;;) { 
216 

/* create table entry */ 
217 
2625 
here.bits = (unsigned char)(len  drop); 
218 
1344 
if (work[sym] + 1U < match) { 
219 
942 
here.op = (unsigned char)0; 
220 
942 
here.val = work[sym]; 
221 

} 
222 
402 
else if (work[sym] >= match) { 
223 
381 
here.op = (unsigned char)(extra[work[sym]  match]); 
224 
381 
here.val = base[work[sym]  match]; 
225 

} 
226 

else { 
227 
21 
here.op = (unsigned char)(32 + 64); /* end of block */ 
228 
21 
here.val = 0; 
229 

} 
230 


231 

/* replicate for those indices with low len bits equal to huff */ 
232 
1344 
incr = 1U << (len  drop); 
233 
1344 
fill = 1U << curr; 
234 
1344 
min = fill; /* save offset to next table */ 
235 

do { 
236 
6276 
fill = incr; 
237 
6276 
next[(huff >> drop) + fill] = here; 
238 
6276 
} while (fill != 0); 
239 


240 

/* backwards increment the lenbit code huff */ 
241 
1344 
incr = 1U << (len  1); 
242 
3969 
while (huff & incr) 
243 
1281 
incr >>= 1; 
244 
1344 
if (incr != 0) { 
245 
1281 
huff &= incr  1; 
246 
1281 
huff += incr; 
247 

} 
248 

else 
249 
63 
huff = 0; 
250 


251 

/* go to next symbol, update count, len */ 
252 
1344 
sym++; 
253 
1344 
if ((count[len]) == 0) { 
254 
279 
if (len == max) break; 
255 
216 
len = lens[work[sym]]; 
256 

} 
257 


258 

/* create new subtable if needed */ 
259 
1281 
if (len > root && (huff & mask) != low) { 
260 

/* if first time, transition to subtables */ 
261 
0 
if (drop == 0) 
262 
0 
drop = root; 
263 


264 

/* increment past last table */ 
265 
0 
next += min; /* here min is 1 << curr */ 
266 


267 

/* determine length of next table */ 
268 
0 
curr = len  drop; 
269 
0 
left = (int)(1 << curr); 
270 
0 
while (curr + drop < max) { 
271 
0 
left = count[curr + drop]; 
272 
0 
if (left <= 0) break; 
273 
0 
curr++; 
274 
0 
left <<= 1; 
275 

} 
276 


277 

/* check for enough space */ 
278 
0 
used += 1U << curr; 
279 
0 
if ((type == LENS && used > ENOUGH_LENS)  
280 
0 
(type == DISTS && used > ENOUGH_DISTS)) 
281 
0 
return 1; 
282 


283 

/* point entry in root table to subtable */ 
284 
0 
low = huff & mask; 
285 
0 
(*table)[low].op = (unsigned char)curr; 
286 
0 
(*table)[low].bits = (unsigned char)root; 
287 
0 
(*table)[low].val = (unsigned short)(next  *table); 
288 

} 
289 

} 
290 


291 

/* fill in remaining table entry if code is incomplete (guaranteed to have 
292 

at most one remaining entry, since if the code is incomplete, the 
293 

maximum code length that was allowed to get this far is one bit) */ 
294 
63 
if (huff != 0) { 
295 
0 
here.op = (unsigned char)64; /* invalid code marker */ 
296 
0 
here.bits = (unsigned char)(len  drop); 
297 
0 
here.val = (unsigned short)0; 
298 
0 
next[huff] = here; 
299 

} 
300 


301 

/* set return parameters */ 
302 
63 
*table += used; 
303 
63 
*bits = root; 
304 
63 
return 0; 
305 

} 