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: int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work)
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: unsigned match; /* use base and extra for symbol >= match */
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: for (len = 0; len <= MAXBITS; len++)
108: count[len] = 0;
109: for (sym = 0; sym < codes; sym++)
110: count[lens[sym]]++;
111:
112: /* bound code lengths, force root to be within code lengths */
113: root = *bits;
114: for (max = MAXBITS; max >= 1; max--)
115: if (count[max] != 0) break;
116: if (root > max) root = max;
117: if (max == 0) { /* no symbols to code at all */
118: here.op = (unsigned char)64; /* invalid code marker */
119: here.bits = (unsigned char)1;
120: here.val = (unsigned short)0;
121: *(*table)++ = here; /* make a table to force an error */
122: *(*table)++ = here;
123: *bits = 1;
124: return 0; /* no symbols, but wait for decoding to report error */
125: }
126: for (min = 1; min < max; min++)
127: if (count[min] != 0) break;
128: if (root < min) root = min;
129:
130: /* check for an over-subscribed or incomplete set of lengths */
131: left = 1;
132: for (len = 1; len <= MAXBITS; len++) {
133: left <<= 1;
134: left -= count[len];
135: if (left < 0) return -1; /* over-subscribed */
136: }
137: 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: offs[1] = 0;
142: for (len = 1; len < MAXBITS; len++)
143: offs[len + 1] = offs[len] + count[len];
144:
145: /* sort symbols by length, by symbol order within each length */
146: for (sym = 0; sym < codes; sym++)
147: 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: switch (type) {
182: case CODES:
183: base = extra = work; /* dummy value--not used */
184: match = 20;
185: break;
186: case LENS:
187: base = lbase;
188: extra = lext;
189: match = 257;
190: break;
191: default: /* DISTS */
192: base = dbase;
193: extra = dext;
194: match = 0;
195: }
196:
197: /* initialize state for loop */
198: huff = 0; /* starting code */
199: sym = 0; /* starting code symbol */
200: len = min; /* starting code length */
201: next = *table; /* current table to fill in */
202: curr = root; /* current table index bits */
203: drop = 0; /* current bits to drop from code for index */
204: low = (unsigned)(-1); /* trigger new sub-table when len > root */
205: used = 1U << root; /* use root table entries */
206: mask = used - 1; /* mask for comparing low */
207:
208: /* check available table space */
209: if ((type == LENS && used > ENOUGH_LENS) ||
210: (type == DISTS && used > ENOUGH_DISTS))
211: return 1;
212:
213: /* process all codes and make table entries */
214: for (;;) {
215: /* create table entry */
216: here.bits = (unsigned char)(len - drop);
217: if (work[sym] + 1u < match) {
218: here.op = (unsigned char)0;
219: here.val = work[sym];
220: }
221: else if (work[sym] >= match) {
222: here.op = (unsigned char)(extra[work[sym] - match]);
223: here.val = base[work[sym] - match];
224: }
225: else {
226: here.op = (unsigned char)(32 + 64); /* end of block */
227: here.val = 0;
228: }
229:
230: /* replicate for those indices with low len bits equal to huff */
231: incr = 1U << (len - drop);
232: fill = 1U << curr;
233: min = fill; /* save offset to next table */
234: do {
235: fill -= incr;
236: next[(huff >> drop) + fill] = here;
237: } while (fill != 0);
238:
239: /* backwards increment the len-bit code huff */
240: incr = 1U << (len - 1);
241: while (huff & incr)
242: incr >>= 1;
243: if (incr != 0) {
244: huff &= incr - 1;
245: huff += incr;
246: }
247: else
248: huff = 0;
249:
250: /* go to next symbol, update count, len */
251: sym++;
252: if (--(count[len]) == 0) {
253: if (len == max) break;
254: len = lens[work[sym]];
255: }
256:
257: /* create new sub-table if needed */
258: if (len > root && (huff & mask) != low) {
259: /* if first time, transition to sub-tables */
260: if (drop == 0)
261: drop = root;
262:
263: /* increment past last table */
264: next += min; /* here min is 1 << curr */
265:
266: /* determine length of next table */
267: curr = len - drop;
268: left = (int)(1 << curr);
269: while (curr + drop < max) {
270: left -= count[curr + drop];
271: if (left <= 0) break;
272: curr++;
273: left <<= 1;
274: }
275:
276: /* check for enough space */
277: used += 1U << curr;
278: if ((type == LENS && used > ENOUGH_LENS) ||
279: (type == DISTS && used > ENOUGH_DISTS))
280: return 1;
281:
282: /* point entry in root table to sub-table */
283: low = huff & mask;
284: (*table)[low].op = (unsigned char)curr;
285: (*table)[low].bits = (unsigned char)root;
286: (*table)[low].val = (unsigned short)(next - *table);
287: }
288: }
289:
290: /* fill in remaining table entry if code is incomplete (guaranteed to have
291: at most one remaining entry, since if the code is incomplete, the
292: maximum code length that was allowed to get this far is one bit) */
293: if (huff != 0) {
294: here.op = (unsigned char)64; /* invalid code marker */
295: here.bits = (unsigned char)(len - drop);
296: here.val = (unsigned short)0;
297: next[huff] = here;
298: }
299:
300: /* set return parameters */
301: *table += used;
302: *bits = root;
303: return 0;
304: }
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>
![[BACK]](/icons/cvsweb/back.gif){kind=icon}
Return to inftrees.c CVS log ![[TXT]](/icons/cvsweb/text.gif){kind=icon}
![[DIR]](/icons/cvsweb/dir.gif){kind=icon}
Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / rsync / zlib