Watt-32 tcp/ip  2.2 dev-rel.10
zinftree.c
1 /* inftrees.c -- generate Huffman trees for efficient decoding
2  * Copyright (C) 1995-2003 Mark Adler
3  * For conditions of distribution and use, see copyright notice in zlib.h
4  */
5 
6 #include "wattcp.h"
7 #include "zutil.h"
8 #include "zinftree.h"
9 
10 #if defined(USE_GZIP) && !defined(Z_NO_INFLATE)
11 
12 #define MAXBITS 15
13 
14 const char inflate_copyright[] =
15  " inflate 1.2.1 Copyright 1995-2003 Mark Adler ";
16 /*
17  If you use the zlib library in a product, an acknowledgment is welcome
18  in the documentation of your product. If for some reason you cannot
19  include such an acknowledgment, I would appreciate that you keep this
20  copyright string in the executable of your product.
21  */
22 
23 /*
24  Build a set of tables to decode the provided canonical Huffman code.
25  The code lengths are lens[0..codes-1]. The result starts at *table,
26  whose indices are 0..2^bits-1. work is a writable array of at least
27  lens shorts, which is used as a work area. type is the type of code
28  to be generated, CODES, LENS, or DISTS. On return, zero is success,
29  -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
30  on return points to the next available entry's address. bits is the
31  requested root table index bits, and on return it is the actual root
32  table index bits. It will differ if the request is greater than the
33  longest code or if it is less than the shortest code.
34  */
35 int inflate_table(type, lens, codes, table, bits, work)
36 codetype type;
37 unsigned short FAR *lens;
38 unsigned codes;
39 code FAR * FAR *table;
40 unsigned FAR *bits;
41 unsigned short FAR *work;
42 {
43  unsigned len; /* a code's length in bits */
44  unsigned sym; /* index of code symbols */
45  unsigned min, max; /* minimum and maximum code lengths */
46  unsigned root; /* number of index bits for root table */
47  unsigned curr; /* number of index bits for current table */
48  unsigned drop; /* code bits to drop for sub-table */
49  int left; /* number of prefix codes available */
50  unsigned used; /* code entries in table used */
51  unsigned huff; /* Huffman code */
52  unsigned incr; /* for incrementing code, index */
53  unsigned fill; /* index for replicating entries */
54  unsigned low; /* low bits for current root entry */
55  unsigned mask; /* mask for low root bits */
56  code this; /* table entry for duplication */
57  code FAR *next; /* next available space in table */
58  const unsigned short FAR *base; /* base value table to use */
59  const unsigned short FAR *extra; /* extra bits table to use */
60  int end; /* use base and extra for symbol > end */
61  unsigned short count[MAXBITS+1]; /* number of codes of each length */
62  unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
63  static const unsigned short lbase[31] = { /* Length codes 257..285 base */
64  3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
65  35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
66  static const unsigned short lext[31] = { /* Length codes 257..285 extra */
67  16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
68  19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 76, 66};
69  static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
70  1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
71  257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
72  8193, 12289, 16385, 24577, 0, 0};
73  static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
74  16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
75  23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
76  28, 28, 29, 29, 64, 64};
77 
78  /*
79  Process a set of code lengths to create a canonical Huffman code. The
80  code lengths are lens[0..codes-1]. Each length corresponds to the
81  symbols 0..codes-1. The Huffman code is generated by first sorting the
82  symbols by length from short to long, and retaining the symbol order
83  for codes with equal lengths. Then the code starts with all zero bits
84  for the first code of the shortest length, and the codes are integer
85  increments for the same length, and zeros are appended as the length
86  increases. For the deflate format, these bits are stored backwards
87  from their more natural integer increment ordering, and so when the
88  decoding tables are built in the large loop below, the integer codes
89  are incremented backwards.
90 
91  This routine assumes, but does not check, that all of the entries in
92  lens[] are in the range 0..MAXBITS. The caller must assure this.
93  1..MAXBITS is interpreted as that code length. zero means that that
94  symbol does not occur in this code.
95 
96  The codes are sorted by computing a count of codes for each length,
97  creating from that a table of starting indices for each length in the
98  sorted table, and then entering the symbols in order in the sorted
99  table. The sorted table is work[], with that space being provided by
100  the caller.
101 
102  The length counts are used for other purposes as well, i.e. finding
103  the minimum and maximum length codes, determining if there are any
104  codes at all, checking for a valid set of lengths, and looking ahead
105  at length counts to determine sub-table sizes when building the
106  decoding tables.
107  */
108 
109  /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
110  for (len = 0; len <= MAXBITS; len++)
111  count[len] = 0;
112  for (sym = 0; sym < codes; sym++)
113  count[lens[sym]]++;
114 
115  /* bound code lengths, force root to be within code lengths */
116  root = *bits;
117  for (max = MAXBITS; max >= 1; max--)
118  if (count[max] != 0) break;
119  if (root > max) root = max;
120  if (max == 0) return -1; /* no codes! */
121  for (min = 1; min <= MAXBITS; min++)
122  if (count[min] != 0) break;
123  if (root < min) root = min;
124 
125  /* check for an over-subscribed or incomplete set of lengths */
126  left = 1;
127  for (len = 1; len <= MAXBITS; len++) {
128  left <<= 1;
129  left -= count[len];
130  if (left < 0) return -1; /* over-subscribed */
131  }
132  if (left > 0 && (type == CODES || (codes - count[0] != 1)))
133  return -1; /* incomplete set */
134 
135  /* generate offsets into symbol table for each length for sorting */
136  offs[1] = 0;
137  for (len = 1; len < MAXBITS; len++)
138  offs[len + 1] = offs[len] + count[len];
139 
140  /* sort symbols by length, by symbol order within each length */
141  for (sym = 0; sym < codes; sym++)
142  if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
143 
144  /*
145  Create and fill in decoding tables. In this loop, the table being
146  filled is at next and has curr index bits. The code being used is huff
147  with length len. That code is converted to an index by dropping drop
148  bits off of the bottom. For codes where len is less than drop + curr,
149  those top drop + curr - len bits are incremented through all values to
150  fill the table with replicated entries.
151 
152  root is the number of index bits for the root table. When len exceeds
153  root, sub-tables are created pointed to by the root entry with an index
154  of the low root bits of huff. This is saved in low to check for when a
155  new sub-table should be started. drop is zero when the root table is
156  being filled, and drop is root when sub-tables are being filled.
157 
158  When a new sub-table is needed, it is necessary to look ahead in the
159  code lengths to determine what size sub-table is needed. The length
160  counts are used for this, and so count[] is decremented as codes are
161  entered in the tables.
162 
163  used keeps track of how many table entries have been allocated from the
164  provided *table space. It is checked when a LENS table is being made
165  against the space in *table, ENOUGH, minus the maximum space needed by
166  the worst case distance code, MAXD. This should never happen, but the
167  sufficiency of ENOUGH has not been proven exhaustively, hence the check.
168  This assumes that when type == LENS, bits == 9.
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 - MAXD)
208  return 1;
209 
210  /* process all codes and make table entries */
211  for (;;) {
212  /* create table entry */
213  this.bits = (unsigned char)(len - drop);
214  if ((int)(work[sym]) < end) {
215  this.op = (unsigned char)0;
216  this.val = work[sym];
217  }
218  else if ((int)(work[sym]) > end) {
219  this.op = (unsigned char)(extra[work[sym]]);
220  this.val = base[work[sym]];
221  }
222  else {
223  this.op = (unsigned char)(32 + 64); /* end of block */
224  this.val = 0;
225  }
226 
227  /* replicate for those indices with low len bits equal to huff */
228  incr = 1U << (len - drop);
229  fill = 1U << curr;
230  do {
231  fill -= incr;
232  next[(huff >> drop) + fill] = this;
233  } while (fill != 0);
234 
235  /* backwards increment the len-bit code huff */
236  incr = 1U << (len - 1);
237  while (huff & incr)
238  incr >>= 1;
239  if (incr != 0) {
240  huff &= incr - 1;
241  huff += incr;
242  }
243  else
244  huff = 0;
245 
246  /* go to next symbol, update count, len */
247  sym++;
248  if (--(count[len]) == 0) {
249  if (len == max) break;
250  len = lens[work[sym]];
251  }
252 
253  /* create new sub-table if needed */
254  if (len > root && (huff & mask) != low) {
255  /* if first time, transition to sub-tables */
256  if (drop == 0)
257  drop = root;
258 
259  /* increment past last table */
260  next += 1U << curr;
261 
262  /* determine length of next table */
263  curr = len - drop;
264  left = (int)(1 << curr);
265  while (curr + drop < max) {
266  left -= count[curr + drop];
267  if (left <= 0) break;
268  curr++;
269  left <<= 1;
270  }
271 
272  /* check for enough space */
273  used += 1U << curr;
274  if (type == LENS && used >= ENOUGH - MAXD)
275  return 1;
276 
277  /* point entry in root table to sub-table */
278  low = huff & mask;
279  (*table)[low].op = (unsigned char)curr;
280  (*table)[low].bits = (unsigned char)root;
281  (*table)[low].val = (unsigned short)(next - *table);
282  }
283  }
284 
285  /*
286  Fill in rest of table for incomplete codes. This loop is similar to the
287  loop above in incrementing huff for table indices. It is assumed that
288  len is equal to curr + drop, so there is no loop needed to increment
289  through high index bits. When the current sub-table is filled, the loop
290  drops back to the root table to fill in any remaining entries there.
291  */
292  this.op = (unsigned char)64; /* invalid code marker */
293  this.bits = (unsigned char)(len - drop);
294  this.val = (unsigned short)0;
295  while (huff != 0) {
296  /* when done with sub-table, drop back to root table */
297  if (drop != 0 && (huff & mask) != low) {
298  drop = 0;
299  len = root;
300  next = *table;
301  curr = root;
302  this.bits = (unsigned char)len;
303  }
304 
305  /* put invalid code marker in table */
306  next[huff >> drop] = this;
307 
308  /* backwards increment the len-bit code huff */
309  incr = 1U << (len - 1);
310  while (huff & incr)
311  incr >>= 1;
312  if (incr != 0) {
313  huff &= incr - 1;
314  huff += incr;
315  }
316  else
317  huff = 0;
318  }
319 
320  /* set return parameters */
321  *table += used;
322  *bits = root;
323  return 0;
324 }
325 #endif /* USE_GZIP && !Z_NO_INFLATE */
326 
Core definitions.
Definition: zinftree.h:24