ยปCore Development>Code coverage>Modules/zlib/inftrees.c

Python code coverage for Modules/zlib/inftrees.c

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