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inftrees.cc
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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(codetype type, unsigned short FAR *lens,
33  unsigned codes, code FAR * FAR *table, unsigned FAR *bits,
34  unsigned short FAR *work)
35 {
36  unsigned len; /* a code's length in bits */
37  unsigned sym; /* index of code symbols */
38  unsigned min, max; /* minimum and maximum code lengths */
39  unsigned root; /* number of index bits for root table */
40  unsigned curr; /* number of index bits for current table */
41  unsigned drop; /* code bits to drop for sub-table */
42  int left; /* number of prefix codes available */
43  unsigned used; /* code entries in table used */
44  unsigned huff; /* Huffman code */
45  unsigned incr; /* for incrementing code, index */
46  unsigned fill; /* index for replicating entries */
47  unsigned low; /* low bits for current root entry */
48  unsigned mask; /* mask for low root bits */
49  code here; /* table entry for duplication */
50  code FAR *next; /* next available space in table */
51  const unsigned short FAR *base; /* base value table to use */
52  const unsigned short FAR *extra; /* extra bits table to use */
53  int end; /* use base and extra for symbol > end */
54  unsigned short count[MAXBITS+1]; /* number of codes of each length */
55  unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
56  static const unsigned short lbase[31] = { /* Length codes 257..285 base */
57  3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
58  35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
59  static const unsigned short lext[31] = { /* Length codes 257..285 extra */
60  16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
61  19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 72, 78};
62  static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
63  1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
64  257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
65  8193, 12289, 16385, 24577, 0, 0};
66  static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
67  16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
68  23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
69  28, 28, 29, 29, 64, 64};
70 
71  /*
72  Process a set of code lengths to create a canonical Huffman code. The
73  code lengths are lens[0..codes-1]. Each length corresponds to the
74  symbols 0..codes-1. The Huffman code is generated by first sorting the
75  symbols by length from short to long, and retaining the symbol order
76  for codes with equal lengths. Then the code starts with all zero bits
77  for the first code of the shortest length, and the codes are integer
78  increments for the same length, and zeros are appended as the length
79  increases. For the deflate format, these bits are stored backwards
80  from their more natural integer increment ordering, and so when the
81  decoding tables are built in the large loop below, the integer codes
82  are incremented backwards.
83 
84  This routine assumes, but does not check, that all of the entries in
85  lens[] are in the range 0..MAXBITS. The caller must assure this.
86  1..MAXBITS is interpreted as that code length. zero means that that
87  symbol does not occur in this code.
88 
89  The codes are sorted by computing a count of codes for each length,
90  creating from that a table of starting indices for each length in the
91  sorted table, and then entering the symbols in order in the sorted
92  table. The sorted table is work[], with that space being provided by
93  the caller.
94 
95  The length counts are used for other purposes as well, i.e. finding
96  the minimum and maximum length codes, determining if there are any
97  codes at all, checking for a valid set of lengths, and looking ahead
98  at length counts to determine sub-table sizes when building the
99  decoding tables.
100  */
101 
102  /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
103  for (len = 0; len <= MAXBITS; len++)
104  count[len] = 0;
105  for (sym = 0; sym < codes; sym++)
106  count[lens[sym]]++;
107 
108  /* bound code lengths, force root to be within code lengths */
109  root = *bits;
110  for (max = MAXBITS; max >= 1; max--)
111  if (count[max] != 0) break;
112  if (root > max) root = max;
113  if (max == 0) { /* no symbols to code at all */
114  here.op = (unsigned char)64; /* invalid code marker */
115  here.bits = (unsigned char)1;
116  here.val = (unsigned short)0;
117  *(*table)++ = here; /* make a table to force an error */
118  *(*table)++ = here;
119  *bits = 1;
120  return 0; /* no symbols, but wait for decoding to report error */
121  }
122  for (min = 1; min < max; min++)
123  if (count[min] != 0) break;
124  if (root < min) root = min;
125 
126  /* check for an over-subscribed or incomplete set of lengths */
127  left = 1;
128  for (len = 1; len <= MAXBITS; len++) {
129  left <<= 1;
130  left -= count[len];
131  if (left < 0) return -1; /* over-subscribed */
132  }
133  if (left > 0 && (type == CODES || max != 1))
134  return -1; /* incomplete set */
135 
136  /* generate offsets into symbol table for each length for sorting */
137  offs[1] = 0;
138  for (len = 1; len < MAXBITS; len++)
139  offs[len + 1] = offs[len] + count[len];
140 
141  /* sort symbols by length, by symbol order within each length */
142  for (sym = 0; sym < codes; sym++)
143  if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
144 
145  /*
146  Create and fill in decoding tables. In this loop, the table being
147  filled is at next and has curr index bits. The code being used is huff
148  with length len. That code is converted to an index by dropping drop
149  bits off of the bottom. For codes where len is less than drop + curr,
150  those top drop + curr - len bits are incremented through all values to
151  fill the table with replicated entries.
152 
153  root is the number of index bits for the root table. When len exceeds
154  root, sub-tables are created pointed to by the root entry with an index
155  of the low root bits of huff. This is saved in low to check for when a
156  new sub-table should be started. drop is zero when the root table is
157  being filled, and drop is root when sub-tables are being filled.
158 
159  When a new sub-table is needed, it is necessary to look ahead in the
160  code lengths to determine what size sub-table is needed. The length
161  counts are used for this, and so count[] is decremented as codes are
162  entered in the tables.
163 
164  used keeps track of how many table entries have been allocated from the
165  provided *table space. It is checked for LENS and DIST tables against
166  the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
167  the initial root table size constants. See the comments in inftrees.h
168  for more information.
169 
170  sym increments through all symbols, and the loop terminates when
171  all codes of length max, i.e. all codes, have been processed. This
172  routine permits incomplete codes, so another loop after this one fills
173  in the rest of the decoding tables with invalid code markers.
174  */
175 
176  /* set up for code type */
177  switch (type) {
178  case CODES:
179  base = extra = work; /* dummy value--not used */
180  end = 19;
181  break;
182  case LENS:
183  base = lbase;
184  base -= 257;
185  extra = lext;
186  extra -= 257;
187  end = 256;
188  break;
189  default: /* DISTS */
190  base = dbase;
191  extra = dext;
192  end = -1;
193  }
194 
195  /* initialize state for loop */
196  huff = 0; /* starting code */
197  sym = 0; /* starting code symbol */
198  len = min; /* starting code length */
199  next = *table; /* current table to fill in */
200  curr = root; /* current table index bits */
201  drop = 0; /* current bits to drop from code for index */
202  low = (unsigned)(-1); /* trigger new sub-table when len > root */
203  used = 1U << root; /* use root table entries */
204  mask = used - 1; /* mask for comparing low */
205 
206  /* check available table space */
207  if ((type == LENS && used > ENOUGH_LENS) ||
208  (type == DISTS && used > ENOUGH_DISTS))
209  return 1;
210 
211  /* process all codes and make table entries */
212  for (;;) {
213  /* create table entry */
214  here.bits = (unsigned char)(len - drop);
215  if ((int)(work[sym]) < end) {
216  here.op = (unsigned char)0;
217  here.val = work[sym];
218  }
219  else if ((int)(work[sym]) > end) {
220  here.op = (unsigned char)(extra[work[sym]]);
221  here.val = base[work[sym]];
222  }
223  else {
224  here.op = (unsigned char)(32 + 64); /* end of block */
225  here.val = 0;
226  }
227 
228  /* replicate for those indices with low len bits equal to huff */
229  incr = 1U << (len - drop);
230  fill = 1U << curr;
231  min = fill; /* save offset to next table */
232  do {
233  fill -= incr;
234  next[(huff >> drop) + fill] = here;
235  } while (fill != 0);
236 
237  /* backwards increment the len-bit code huff */
238  incr = 1U << (len - 1);
239  while (huff & incr)
240  incr >>= 1;
241  if (incr != 0) {
242  huff &= incr - 1;
243  huff += incr;
244  }
245  else
246  huff = 0;
247 
248  /* go to next symbol, update count, len */
249  sym++;
250  if (--(count[len]) == 0) {
251  if (len == max) break;
252  len = lens[work[sym]];
253  }
254 
255  /* create new sub-table if needed */
256  if (len > root && (huff & mask) != low) {
257  /* if first time, transition to sub-tables */
258  if (drop == 0)
259  drop = root;
260 
261  /* increment past last table */
262  next += min; /* here min is 1 << curr */
263 
264  /* determine length of next table */
265  curr = len - drop;
266  left = (int)(1 << curr);
267  while (curr + drop < max) {
268  left -= count[curr + drop];
269  if (left <= 0) break;
270  curr++;
271  left <<= 1;
272  }
273 
274  /* check for enough space */
275  used += 1U << curr;
276  if ((type == LENS && used > ENOUGH_LENS) ||
277  (type == DISTS && used > ENOUGH_DISTS))
278  return 1;
279 
280  /* point entry in root table to sub-table */
281  low = huff & mask;
282  (*table)[low].op = (unsigned char)curr;
283  (*table)[low].bits = (unsigned char)root;
284  (*table)[low].val = (unsigned short)(next - *table);
285  }
286  }
287 
288  /* fill in remaining table entry if code is incomplete (guaranteed to have
289  at most one remaining entry, since if the code is incomplete, the
290  maximum code length that was allowed to get this far is one bit) */
291  if (huff != 0) {
292  here.op = (unsigned char)64; /* invalid code marker */
293  here.bits = (unsigned char)(len - drop);
294  here.val = (unsigned short)0;
295  next[huff] = here;
296  }
297 
298  /* set return parameters */
299  *table += used;
300  *bits = root;
301  return 0;
302 }
const XML_Char int len
Definition: expat.h:262
int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens, unsigned codes, code FAR *FAR *table, unsigned FAR *bits, unsigned short FAR *work)
Definition: inftrees.cc:32
unsigned short val
Definition: inftrees.h:27
#define ZLIB_INTERNAL
Definition: compress.cc:8
static ush mask[]
Definition: csz_inflate.cc:317
Definition: inftrees.h:57
unsigned char op
Definition: inftrees.h:25
const XML_Char int const XML_Char int const XML_Char * base
Definition: expat.h:331
#define ENOUGH_LENS
Definition: inftrees.h:49
Definition: inftrees.h:55
typedef int(XMLCALL *XML_NotStandaloneHandler)(void *userData)
unsigned char bits
Definition: inftrees.h:26
#define ENOUGH_DISTS
Definition: inftrees.h:50
codetype
Definition: inftrees.h:54
Definition: inftrees.h:24
T max(const T t1, const T t2)
brief Return the largest of the two arguments
T min(const T t1, const T t2)
brief Return the smallest of the two arguments
Definition: inftrees.h:56
#define MAXBITS
Definition: inftrees.cc:9