1  /* inftrees.c  generate Huffman trees for efficient decoding


2  * Copyright (C) 19952013 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 19952013 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..codes1]. The result starts at *table,


23  whose indices are 0..2^bits1. 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 subtable */


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  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, 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..codes1]. Each length corresponds to the


78  symbols 0..codes1. 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 subtable 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 oversubscribed 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; /* oversubscribed */


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, subtables 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 subtable should be started. drop is zero when the root table is


161  being filled, and drop is root when subtables are being filled.


162 


163  When a new subtable is needed, it is necessary to look ahead in the


164  code lengths to determine what size subtable 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 valuenot used */


184  end = 19;


185  break;


186  case LENS:


187  base = lbase;


188  base = 257;


189  extra = lext;


190  extra = 257;


191  end = 256;


192  break;


193  default: /* DISTS */


194  base = dbase;


195  extra = dext;


196  end = 1;


197  }


198 


199  /* initialize state for loop */


200  huff = 0; /* starting code */


201  sym = 0; /* starting code symbol */


202  len = min; /* starting code length */


203  next = *table; /* current table to fill in */


204  curr = root; /* current table index bits */


205  drop = 0; /* current bits to drop from code for index */


206  low = (unsigned)(1); /* trigger new subtable when len > root */


207  used = 1U << root; /* use root table entries */


208  mask = used  1; /* mask for comparing low */


209 


210  /* check available table space */


211  if ((type == LENS && used > ENOUGH_LENS) 


212  (type == DISTS && used > ENOUGH_DISTS))


213  return 1;


214 


215  /* process all codes and make table entries */


216  for (;;) {


217  /* create table entry */


218  here.bits = (unsigned char)(len  drop);


219  if ((int)(work[sym]) < end) {


220  here.op = (unsigned char)0;


221  here.val = work[sym];


222  }


223  else if ((int)(work[sym]) > end) {


224  here.op = (unsigned char)(extra[work[sym]]);


225  here.val = base[work[sym]];


226  }


227  else {


228  here.op = (unsigned char)(32 + 64); /* end of block */


229  here.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] = here;


239  } while (fill != 0);


240 


241  /* backwards increment the lenbit 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 subtable if needed */


260  if (len > root && (huff & mask) != low) {


261  /* if first time, transition to subtables */


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_LENS) 


281  (type == DISTS && used > ENOUGH_DISTS))


282  return 1;


283 


284  /* point entry in root table to subtable */


285  low = huff & mask;


286  (*table)[low].op = (unsigned char)curr;


287  (*table)[low].bits = (unsigned char)root;


288  (*table)[low].val = (unsigned short)(next  *table);


289  }


290  }


291 


292  /* fill in remaining table entry if code is incomplete (guaranteed to have


293  at most one remaining entry, since if the code is incomplete, the


294  maximum code length that was allowed to get this far is one bit) */


295  if (huff != 0) {


296  here.op = (unsigned char)64; /* invalid code marker */


297  here.bits = (unsigned char)(len  drop);


298  here.val = (unsigned short)0;


299  next[huff] = here;


300  }


301 


302  /* set return parameters */


303  *table += used;


304  *bits = root;


305  return 0;


306  }

