inftrees.c
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1 /* inftrees.c -- generate Huffman trees for efficient decoding
2  * Copyright (C) 1995-2005 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 1.2.3 Copyright 1995-2005 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 inflate_table(type, lens, codes, table, bits, work)
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 this; /* 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, 201, 196};
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  this.op = (unsigned char)64; /* invalid code marker */
119  this.bits = (unsigned char)1;
120  this.val = (unsigned short)0;
121  *(*table)++ = this; /* make a table to force an error */
122  *(*table)++ = this;
123  *bits = 1;
124  return 0; /* no symbols, but wait for decoding to report error */
125  }
126  for (min = 1; min <= MAXBITS; 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 when a LENS table is being made
170  against the space in *table, ENOUGH, minus the maximum space needed by
171  the worst case distance code, MAXD. This should never happen, but the
172  sufficiency of ENOUGH has not been proven exhaustively, hence the check.
173  This assumes that when type == LENS, bits == 9.
174 
175  sym increments through all symbols, and the loop terminates when
176  all codes of length max, i.e. all codes, have been processed. This
177  routine permits incomplete codes, so another loop after this one fills
178  in the rest of the decoding tables with invalid code markers.
179  */
180 
181  /* set up for code type */
182  switch (type) {
183  case CODES:
184  base = extra = work; /* dummy value--not used */
185  end = 19;
186  break;
187  case LENS:
188  base = lbase;
189  base -= 257;
190  extra = lext;
191  extra -= 257;
192  end = 256;
193  break;
194  default: /* DISTS */
195  base = dbase;
196  extra = dext;
197  end = -1;
198  }
199 
200  /* initialize state for loop */
201  huff = 0; /* starting code */
202  sym = 0; /* starting code symbol */
203  len = min; /* starting code length */
204  next = *table; /* current table to fill in */
205  curr = root; /* current table index bits */
206  drop = 0; /* current bits to drop from code for index */
207  low = (unsigned)(-1); /* trigger new sub-table when len > root */
208  used = 1U << root; /* use root table entries */
209  mask = used - 1; /* mask for comparing low */
210 
211  /* check available table space */
212  if (type == LENS && used >= ENOUGH - MAXD)
213  return 1;
214 
215  /* process all codes and make table entries */
216  for (;;) {
217  /* create table entry */
218  this.bits = (unsigned char)(len - drop);
219  if ((int)(work[sym]) < end) {
220  this.op = (unsigned char)0;
221  this.val = work[sym];
222  }
223  else if ((int)(work[sym]) > end) {
224  this.op = (unsigned char)(extra[work[sym]]);
225  this.val = base[work[sym]];
226  }
227  else {
228  this.op = (unsigned char)(32 + 64); /* end of block */
229  this.val = 0;
230  }
231 
232  /* replicate for those indices with low len bits equal to huff */
233  incr = 1U << (len - drop);
234  fill = 1U << curr;
235  min = fill; /* save offset to next table */
236  do {
237  fill -= incr;
238  next[(huff >> drop) + fill] = this;
239  } while (fill != 0);
240 
241  /* backwards increment the len-bit code huff */
242  incr = 1U << (len - 1);
243  while (huff & incr)
244  incr >>= 1;
245  if (incr != 0) {
246  huff &= incr - 1;
247  huff += incr;
248  }
249  else
250  huff = 0;
251 
252  /* go to next symbol, update count, len */
253  sym++;
254  if (--(count[len]) == 0) {
255  if (len == max) break;
256  len = lens[work[sym]];
257  }
258 
259  /* create new sub-table if needed */
260  if (len > root && (huff & mask) != low) {
261  /* if first time, transition to sub-tables */
262  if (drop == 0)
263  drop = root;
264 
265  /* increment past last table */
266  next += min; /* here min is 1 << curr */
267 
268  /* determine length of next table */
269  curr = len - drop;
270  left = (int)(1 << curr);
271  while (curr + drop < max) {
272  left -= count[curr + drop];
273  if (left <= 0) break;
274  curr++;
275  left <<= 1;
276  }
277 
278  /* check for enough space */
279  used += 1U << curr;
280  if (type == LENS && used >= ENOUGH - MAXD)
281  return 1;
282 
283  /* point entry in root table to sub-table */
284  low = huff & mask;
285  (*table)[low].op = (unsigned char)curr;
286  (*table)[low].bits = (unsigned char)root;
287  (*table)[low].val = (unsigned short)(next - *table);
288  }
289  }
290 
291  /*
292  Fill in rest of table for incomplete codes. This loop is similar to the
293  loop above in incrementing huff for table indices. It is assumed that
294  len is equal to curr + drop, so there is no loop needed to increment
295  through high index bits. When the current sub-table is filled, the loop
296  drops back to the root table to fill in any remaining entries there.
297  */
298  this.op = (unsigned char)64; /* invalid code marker */
299  this.bits = (unsigned char)(len - drop);
300  this.val = (unsigned short)0;
301  while (huff != 0) {
302  /* when done with sub-table, drop back to root table */
303  if (drop != 0 && (huff & mask) != low) {
304  drop = 0;
305  len = root;
306  next = *table;
307  this.bits = (unsigned char)len;
308  }
309 
310  /* put invalid code marker in table */
311  next[huff >> drop] = this;
312 
313  /* backwards increment the len-bit code huff */
314  incr = 1U << (len - 1);
315  while (huff & incr)
316  incr >>= 1;
317  if (incr != 0) {
318  huff &= incr - 1;
319  huff += incr;
320  }
321  else
322  huff = 0;
323  }
324 
325  /* set return parameters */
326  *table += used;
327  *bits = root;
328  return 0;
329 }
png_infop png_charp png_int_32 png_int_32 int * type
Definition: png.h:2332
#define ENOUGH
Definition: inftrees.h:43
static int min(int a, int b)
int inflate_table(codetype type, unsigned short FAR *lens, unsigned codes, code FAR *FAR *table, unsigned FAR *bits, unsigned short FAR *work)
Definition: inftrees.c:32
Definition: inftrees.h:48
png_infop int png_uint_32 mask
Definition: png.h:2081
const char inflate_copyright[]
Definition: inftrees.c:11
#define FAR
Definition: jmorecfg.h:215
int val
Definition: jpeglib.h:956
codetype
Definition: inftrees.h:47
Definition: inftrees.h:24
#define MAXBITS
Definition: inftrees.c:9
typedef int
Definition: png.h:1113
Definition: inftrees.h:49
static int max(int a, int b)
#define MAXD
Definition: inftrees.h:44


openhrp3
Author(s): AIST, General Robotix Inc., Nakamura Lab of Dept. of Mechano Informatics at University of Tokyo
autogenerated on Sat May 8 2021 02:42:38