Python code coverage for Modules/zlib/inftrees.c

#	count	content
1	n/a	/* inftrees.c -- generate Huffman trees for efficient decoding
2	n/a	* Copyright (C) 1995-2017 Mark Adler
3	n/a	* For conditions of distribution and use, see copyright notice in zlib.h
4	n/a	*/
5	n/a
6	n/a	#include "zutil.h"
7	n/a	#include "inftrees.h"
8	n/a
9	n/a	#define MAXBITS 15
10	n/a
11	n/a	const char inflate_copyright[] =
12	n/a	" inflate 1.2.11 Copyright 1995-2017 Mark Adler ";
13	n/a	/*
14	n/a	If you use the zlib library in a product, an acknowledgment is welcome
15	n/a	in the documentation of your product. If for some reason you cannot
16	n/a	include such an acknowledgment, I would appreciate that you keep this
17	n/a	copyright string in the executable of your product.
18	n/a	*/
19	n/a
20	n/a	/*
21	n/a	Build a set of tables to decode the provided canonical Huffman code.
22	n/a	The code lengths are lens[0..codes-1]. The result starts at *table,
23	n/a	whose indices are 0..2^bits-1. work is a writable array of at least
24	n/a	lens shorts, which is used as a work area. type is the type of code
25	n/a	to be generated, CODES, LENS, or DISTS. On return, zero is success,
26	n/a	-1 is an invalid code, and +1 means that ENOUGH isn't enough. table
27	n/a	on return points to the next available entry's address. bits is the
28	n/a	requested root table index bits, and on return it is the actual root
29	n/a	table index bits. It will differ if the request is greater than the
30	n/a	longest code or if it is less than the shortest code.
31	n/a	*/
32	n/a	int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work)
33	n/a	codetype type;
34	n/a	unsigned short FAR *lens;
35	n/a	unsigned codes;
36	n/a	code FAR * FAR *table;
37	n/a	unsigned FAR *bits;
38	n/a	unsigned short FAR *work;
39	n/a	{
40	n/a	unsigned len; /* a code's length in bits */
41	n/a	unsigned sym; /* index of code symbols */
42	n/a	unsigned min, max; /* minimum and maximum code lengths */
43	n/a	unsigned root; /* number of index bits for root table */
44	n/a	unsigned curr; /* number of index bits for current table */
45	n/a	unsigned drop; /* code bits to drop for sub-table */
46	n/a	int left; /* number of prefix codes available */
47	n/a	unsigned used; /* code entries in table used */
48	n/a	unsigned huff; /* Huffman code */
49	n/a	unsigned incr; /* for incrementing code, index */
50	n/a	unsigned fill; /* index for replicating entries */
51	n/a	unsigned low; /* low bits for current root entry */
52	n/a	unsigned mask; /* mask for low root bits */
53	n/a	code here; /* table entry for duplication */
54	n/a	code FAR next; / next available space in table */
55	n/a	const unsigned short FAR base; / base value table to use */
56	n/a	const unsigned short FAR extra; / extra bits table to use */
57	n/a	unsigned match; /* use base and extra for symbol >= match */
58	n/a	unsigned short count[MAXBITS+1]; /* number of codes of each length */
59	n/a	unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
60	n/a	static const unsigned short lbase[31] = { /* Length codes 257..285 base */
61	n/a	3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
62	n/a	35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
63	n/a	static const unsigned short lext[31] = { /* Length codes 257..285 extra */
64	n/a	16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
65	n/a	19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 77, 202};
66	n/a	static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
67	n/a	1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
68	n/a	257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
69	n/a	8193, 12289, 16385, 24577, 0, 0};
70	n/a	static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
71	n/a	16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
72	n/a	23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
73	n/a	28, 28, 29, 29, 64, 64};
74	n/a
75	n/a	/*
76	n/a	Process a set of code lengths to create a canonical Huffman code. The
77	n/a	code lengths are lens[0..codes-1]. Each length corresponds to the
78	n/a	symbols 0..codes-1. The Huffman code is generated by first sorting the
79	n/a	symbols by length from short to long, and retaining the symbol order
80	n/a	for codes with equal lengths. Then the code starts with all zero bits
81	n/a	for the first code of the shortest length, and the codes are integer
82	n/a	increments for the same length, and zeros are appended as the length
83	n/a	increases. For the deflate format, these bits are stored backwards
84	n/a	from their more natural integer increment ordering, and so when the
85	n/a	decoding tables are built in the large loop below, the integer codes
86	n/a	are incremented backwards.
87	n/a
88	n/a	This routine assumes, but does not check, that all of the entries in
89	n/a	lens[] are in the range 0..MAXBITS. The caller must assure this.
90	n/a	1..MAXBITS is interpreted as that code length. zero means that that
91	n/a	symbol does not occur in this code.
92	n/a
93	n/a	The codes are sorted by computing a count of codes for each length,
94	n/a	creating from that a table of starting indices for each length in the
95	n/a	sorted table, and then entering the symbols in order in the sorted
96	n/a	table. The sorted table is work[], with that space being provided by
97	n/a	the caller.
98	n/a
99	n/a	The length counts are used for other purposes as well, i.e. finding
100	n/a	the minimum and maximum length codes, determining if there are any
101	n/a	codes at all, checking for a valid set of lengths, and looking ahead
102	n/a	at length counts to determine sub-table sizes when building the
103	n/a	decoding tables.
104	n/a	*/
105	n/a
106	n/a	/* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
107	n/a	for (len = 0; len <= MAXBITS; len++)
108	n/a	count[len] = 0;
109	n/a	for (sym = 0; sym < codes; sym++)
110	n/a	count[lens[sym]]++;
111	n/a
112	n/a	/* bound code lengths, force root to be within code lengths */
113	n/a	root = *bits;
114	n/a	for (max = MAXBITS; max >= 1; max--)
115	n/a	if (count[max] != 0) break;
116	n/a	if (root > max) root = max;
117	n/a	if (max == 0) { /* no symbols to code at all */
118	n/a	here.op = (unsigned char)64; /* invalid code marker */
119	n/a	here.bits = (unsigned char)1;
120	n/a	here.val = (unsigned short)0;
121	n/a	(table)++ = here; /* make a table to force an error */
122	n/a	(table)++ = here;
123	n/a	*bits = 1;
124	n/a	return 0; /* no symbols, but wait for decoding to report error */
125	n/a	}
126	n/a	for (min = 1; min < max; min++)
127	n/a	if (count[min] != 0) break;
128	n/a	if (root < min) root = min;
129	n/a
130	n/a	/* check for an over-subscribed or incomplete set of lengths */
131	n/a	left = 1;
132	n/a	for (len = 1; len <= MAXBITS; len++) {
133	n/a	left <<= 1;
134	n/a	left -= count[len];
135	n/a	if (left < 0) return -1; /* over-subscribed */
136	n/a	}
137	n/a	if (left > 0 && (type == CODES \|\| max != 1))
138	n/a	return -1; /* incomplete set */
139	n/a
140	n/a	/* generate offsets into symbol table for each length for sorting */
141	n/a	offs[1] = 0;
142	n/a	for (len = 1; len < MAXBITS; len++)
143	n/a	offs[len + 1] = offs[len] + count[len];
144	n/a
145	n/a	/* sort symbols by length, by symbol order within each length */
146	n/a	for (sym = 0; sym < codes; sym++)
147	n/a	if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
148	n/a
149	n/a	/*
150	n/a	Create and fill in decoding tables. In this loop, the table being
151	n/a	filled is at next and has curr index bits. The code being used is huff
152	n/a	with length len. That code is converted to an index by dropping drop
153	n/a	bits off of the bottom. For codes where len is less than drop + curr,
154	n/a	those top drop + curr - len bits are incremented through all values to
155	n/a	fill the table with replicated entries.
156	n/a
157	n/a	root is the number of index bits for the root table. When len exceeds
158	n/a	root, sub-tables are created pointed to by the root entry with an index
159	n/a	of the low root bits of huff. This is saved in low to check for when a
160	n/a	new sub-table should be started. drop is zero when the root table is
161	n/a	being filled, and drop is root when sub-tables are being filled.
162	n/a
163	n/a	When a new sub-table is needed, it is necessary to look ahead in the
164	n/a	code lengths to determine what size sub-table is needed. The length
165	n/a	counts are used for this, and so count[] is decremented as codes are
166	n/a	entered in the tables.
167	n/a
168	n/a	used keeps track of how many table entries have been allocated from the
169	n/a	provided *table space. It is checked for LENS and DIST tables against
170	n/a	the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
171	n/a	the initial root table size constants. See the comments in inftrees.h
172	n/a	for more information.
173	n/a
174	n/a	sym increments through all symbols, and the loop terminates when
175	n/a	all codes of length max, i.e. all codes, have been processed. This
176	n/a	routine permits incomplete codes, so another loop after this one fills
177	n/a	in the rest of the decoding tables with invalid code markers.
178	n/a	*/
179	n/a
180	n/a	/* set up for code type */
181	n/a	switch (type) {
182	n/a	case CODES:
183	n/a	base = extra = work; /* dummy value--not used */
184	n/a	match = 20;
185	n/a	break;
186	n/a	case LENS:
187	n/a	base = lbase;
188	n/a	extra = lext;
189	n/a	match = 257;
190	n/a	break;
191	n/a	default: /* DISTS */
192	n/a	base = dbase;
193	n/a	extra = dext;
194	n/a	match = 0;
195	n/a	}
196	n/a
197	n/a	/* initialize state for loop */
198	n/a	huff = 0; /* starting code */
199	n/a	sym = 0; /* starting code symbol */
200	n/a	len = min; /* starting code length */
201	n/a	next = table; / current table to fill in */
202	n/a	curr = root; /* current table index bits */
203	n/a	drop = 0; /* current bits to drop from code for index */
204	n/a	low = (unsigned)(-1); /* trigger new sub-table when len > root */
205	n/a	used = 1U << root; /* use root table entries */
206	n/a	mask = used - 1; /* mask for comparing low */
207	n/a
208	n/a	/* check available table space */
209	n/a	if ((type == LENS && used > ENOUGH_LENS) \|\|
210	n/a	(type == DISTS && used > ENOUGH_DISTS))
211	n/a	return 1;
212	n/a
213	n/a	/* process all codes and make table entries */
214	n/a	for (;;) {
215	n/a	/* create table entry */
216	n/a	here.bits = (unsigned char)(len - drop);
217	n/a	if (work[sym] + 1U < match) {
218	n/a	here.op = (unsigned char)0;
219	n/a	here.val = work[sym];
220	n/a	}
221	n/a	else if (work[sym] >= match) {
222	n/a	here.op = (unsigned char)(extra[work[sym] - match]);
223	n/a	here.val = base[work[sym] - match];
224	n/a	}
225	n/a	else {
226	n/a	here.op = (unsigned char)(32 + 64); /* end of block */
227	n/a	here.val = 0;
228	n/a	}
229	n/a
230	n/a	/* replicate for those indices with low len bits equal to huff */
231	n/a	incr = 1U << (len - drop);
232	n/a	fill = 1U << curr;
233	n/a	min = fill; /* save offset to next table */
234	n/a	do {
235	n/a	fill -= incr;
236	n/a	next[(huff >> drop) + fill] = here;
237	n/a	} while (fill != 0);
238	n/a
239	n/a	/* backwards increment the len-bit code huff */
240	n/a	incr = 1U << (len - 1);
241	n/a	while (huff & incr)
242	n/a	incr >>= 1;
243	n/a	if (incr != 0) {
244	n/a	huff &= incr - 1;
245	n/a	huff += incr;
246	n/a	}
247	n/a	else
248	n/a	huff = 0;
249	n/a
250	n/a	/* go to next symbol, update count, len */
251	n/a	sym++;
252	n/a	if (--(count[len]) == 0) {
253	n/a	if (len == max) break;
254	n/a	len = lens[work[sym]];
255	n/a	}
256	n/a
257	n/a	/* create new sub-table if needed */
258	n/a	if (len > root && (huff & mask) != low) {
259	n/a	/* if first time, transition to sub-tables */
260	n/a	if (drop == 0)
261	n/a	drop = root;
262	n/a
263	n/a	/* increment past last table */
264	n/a	next += min; /* here min is 1 << curr */
265	n/a
266	n/a	/* determine length of next table */
267	n/a	curr = len - drop;
268	n/a	left = (int)(1 << curr);
269	n/a	while (curr + drop < max) {
270	n/a	left -= count[curr + drop];
271	n/a	if (left <= 0) break;
272	n/a	curr++;
273	n/a	left <<= 1;
274	n/a	}
275	n/a
276	n/a	/* check for enough space */
277	n/a	used += 1U << curr;
278	n/a	if ((type == LENS && used > ENOUGH_LENS) \|\|
279	n/a	(type == DISTS && used > ENOUGH_DISTS))
280	n/a	return 1;
281	n/a
282	n/a	/* point entry in root table to sub-table */
283	n/a	low = huff & mask;
284	n/a	(*table)[low].op = (unsigned char)curr;
285	n/a	(*table)[low].bits = (unsigned char)root;
286	n/a	(table)[low].val = (unsigned short)(next - table);
287	n/a	}
288	n/a	}
289	n/a
290	n/a	/* fill in remaining table entry if code is incomplete (guaranteed to have
291	n/a	at most one remaining entry, since if the code is incomplete, the
292	n/a	maximum code length that was allowed to get this far is one bit) */
293	n/a	if (huff != 0) {
294	n/a	here.op = (unsigned char)64; /* invalid code marker */
295	n/a	here.bits = (unsigned char)(len - drop);
296	n/a	here.val = (unsigned short)0;
297	n/a	next[huff] = here;
298	n/a	}
299	n/a
300	n/a	/* set return parameters */
301	n/a	*table += used;
302	n/a	*bits = root;
303	n/a	return 0;
304	n/a	}