File Coverage

cpan/Compress-Raw-Zlib/inftrees.c
Criterion Covered Total %
statement 75 86 87.2
branch n/a
condition n/a
subroutine n/a
total 75 86 87.2


line stmt bran cond sub time code
1           /* inftrees.c -- generate Huffman trees for efficient decoding
2           * Copyright (C) 1995-2013 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 1.2.8 Copyright 1995-2013 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 36660         int ZLIB_INTERNAL inflate_table(
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           int end; /* use base and extra for symbol > end */
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, 72, 78};
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 623220         for (len = 0; len <= MAXBITS; len++)
108 586560         count[len] = 0;
109 3479996         for (sym = 0; sym < codes; sym++)
110 3479996         count[lens[sym]]++;
111            
112           /* bound code lengths, force root to be within code lengths */
113 36660         root = *bits;
114 436704         for (max = MAXBITS; max >= 1; max--)
115 436704         if (count[max] != 0) break;
116 36660         if (root > max) root = max;
117 36660         if (max == 0) { /* no symbols to code at all */
118 0         here.op = (unsigned char)64; /* invalid code marker */
119 0         here.bits = (unsigned char)1;
120 0         here.val = (unsigned short)0;
121 0         *(*table)++ = here; /* make a table to force an error */
122 0         *(*table)++ = here;
123 0         *bits = 1;
124 0         return 0; /* no symbols, but wait for decoding to report error */
125           }
126 36562         for (min = 1; min < max; min++)
127 61704         if (count[min] != 0) break;
128 36660         if (root < min) root = min;
129            
130           /* check for an over-subscribed or incomplete set of lengths */
131           left = 1;
132 586560         for (len = 1; len <= MAXBITS; len++) {
133 549900         left <<= 1;
134 549900         left -= count[len];
135 549900         if (left < 0) return -1; /* over-subscribed */
136           }
137 36660         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 36622         offs[1] = 0;
142 549330         for (len = 1; len < MAXBITS; len++)
143 512708         offs[len + 1] = offs[len] + count[len];
144            
145           /* sort symbols by length, by symbol order within each length */
146 3479274         for (sym = 0; sym < codes; sym++)
147 3479274         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 36622         switch (type) {
182           case CODES:
183           base = extra = work; /* dummy value--not used */
184           end = 19;
185 12866         break;
186           case LENS:
187           base = lbase;
188           base -= 257;
189           extra = lext;
190           extra -= 257;
191           end = 256;
192           break;
193           default: /* DISTS */
194           base = dbase;
195           extra = dext;
196           end = -1;
197           }
198            
199           /* initialize state for loop */
200           huff = 0; /* starting code */
201           sym = 0; /* starting code symbol */
202           len = min; /* starting code length */
203 36622         next = *table; /* current table to fill in */
204           curr = root; /* current table index bits */
205           drop = 0; /* current bits to drop from code for index */
206           low = (unsigned)(-1); /* trigger new sub-table when len > root */
207 36622         used = 1U << root; /* use root table entries */
208 36622         mask = used - 1; /* mask for comparing low */
209            
210           /* check available table space */
211 73244         if ((type == LENS && used > ENOUGH_LENS) ||
212 36622         (type == DISTS && used > ENOUGH_DISTS))
213           return 1;
214            
215           /* process all codes and make table entries */
216           for (;;) {
217           /* create table entry */
218 405650         here.bits = (unsigned char)(len - drop);
219 405650         if ((int)(work[sym]) < end) {
220 339052         here.op = (unsigned char)0;
221 339052         here.val = work[sym];
222           }
223 66598         else if ((int)(work[sym]) > end) {
224 54720         here.op = (unsigned char)(extra[work[sym]]);
225 54720         here.val = base[work[sym]];
226           }
227           else {
228 11878         here.op = (unsigned char)(32 + 64); /* end of block */
229 11878         here.val = 0;
230           }
231            
232           /* replicate for those indices with low len bits equal to huff */
233 405650         incr = 1U << (len - drop);
234 405650         fill = 1U << curr;
235           min = fill; /* save offset to next table */
236           do {
237 1270086         fill -= incr;
238 1270086         next[(huff >> drop) + fill] = here;
239 1270086         } while (fill != 0);
240            
241           /* backwards increment the len-bit code huff */
242 405650         incr = 1U << (len - 1);
243 1180328         while (huff & incr)
244 369028         incr >>= 1;
245 405650         if (incr != 0) {
246 369028         huff &= incr - 1;
247 369028         huff += incr;
248           }
249           else
250           huff = 0;
251            
252           /* go to next symbol, update count, len */
253 405650         sym++;
254 405650         if (--(count[len]) == 0) {
255 112564         if (len == max) break;
256 75942         len = lens[work[sym]];
257           }
258            
259           /* create new sub-table if needed */
260 369028         if (len > root && (huff & mask) != low) {
261           /* if first time, transition to sub-tables */
262 1830         if (drop == 0)
263           drop = root;
264            
265           /* increment past last table */
266 1830         next += min; /* here min is 1 << curr */
267            
268           /* determine length of next table */
269 1830         curr = len - drop;
270 1830         left = (int)(1 << curr);
271 4352         while (curr + drop < max) {
272 2272         left -= count[curr + drop];
273 2272         if (left <= 0) break;
274 692         curr++;
275 692         left <<= 1;
276           }
277            
278           /* check for enough space */
279 1830         used += 1U << curr;
280 3660         if ((type == LENS && used > ENOUGH_LENS) ||
281 1830         (type == DISTS && used > ENOUGH_DISTS))
282           return 1;
283            
284           /* point entry in root table to sub-table */
285 1830         low = huff & mask;
286 1830         (*table)[low].op = (unsigned char)curr;
287 1830         (*table)[low].bits = (unsigned char)root;
288 1830         (*table)[low].val = (unsigned short)(next - *table);
289           }
290           }
291            
292           /* fill in remaining table entry if code is incomplete (guaranteed to have
293           at most one remaining entry, since if the code is incomplete, the
294           maximum code length that was allowed to get this far is one bit) */
295 36622         if (huff != 0) {
296 0         here.op = (unsigned char)64; /* invalid code marker */
297 0         here.bits = (unsigned char)(len - drop);
298 0         here.val = (unsigned short)0;
299 0         next[huff] = here;
300           }
301            
302           /* set return parameters */
303 36622         *table += used;
304 36622         *bits = root;
305 36622         return 0;
306           }