1 /* trees.c -- output deflated data using Huffman coding

     2  * Copyright (C) 1995-1998 Jean-loup Gailly

     3  * For conditions of distribution and use, see copyright notice in zlib.h 

     4  */

     5 

     6 /*

     7  *  ALGORITHM

     8  *

     9  *      The "deflation" process uses several Huffman trees. The more

    10  *      common source values are represented by shorter bit sequences.

    11  *

    12  *      Each code tree is stored in a compressed form which is itself

    13  * a Huffman encoding of the lengths of all the code strings (in

    14  * ascending order by source values).  The actual code strings are

    15  * reconstructed from the lengths in the inflate process, as described

    16  * in the deflate specification.

    17  *

    18  *  REFERENCES

    19  *

    20  *      Deutsch, L.P.,"'Deflate' Compressed Data Format Specification".

    21  *      Available in ftp.uu.net:/pub/archiving/zip/doc/deflate-1.1.doc

    22  *

    23  *      Storer, James A.

    24  *          Data Compression:  Methods and Theory, pp. 49-50.

    25  *          Computer Science Press, 1988.  ISBN 0-7167-8156-5.

    26  *

    27  *      Sedgewick, R.

    28  *          Algorithms, p290.

    29  *          Addison-Wesley, 1983. ISBN 0-201-06672-6.

    30  */

    31 

    32 /* @(#) $Id$ */

    33 

    34 /* #define GEN_TREES_H */

    35 

    36 #include "deflate.h"

    37 

    38 #ifdef DEBUG

    39 #  include <ctype.h>

    40 #endif

    41 

    42 /* ===========================================================================

    43  * Constants

    44  */

    45 

    46 #define MAX_BL_BITS 7

    47 /* Bit length codes must not exceed MAX_BL_BITS bits */

    48 

    49 #define END_BLOCK 256

    50 /* end of block literal code */

    51 

    52 #define REP_3_6      16

    53 /* repeat previous bit length 3-6 times (2 bits of repeat count) */

    54 

    55 #define REPZ_3_10    17

    56 /* repeat a zero length 3-10 times  (3 bits of repeat count) */

    57 

    58 #define REPZ_11_138  18

    59 /* repeat a zero length 11-138 times  (7 bits of repeat count) */

    60 

    61 local const int extra_lbits[LENGTH_CODES] /* extra bits for each length code */

    62    = {0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0};

    63 

    64 local const int extra_dbits[D_CODES] /* extra bits for each distance code */

    65    = {0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13};

    66 

    67 local const int extra_blbits[BL_CODES]/* extra bits for each bit length code */

    68    = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7};

    69 

    70 local const uch bl_order[BL_CODES]

    71    = {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};

    72 /* The lengths of the bit length codes are sent in order of decreasing

    73  * probability, to avoid transmitting the lengths for unused bit length codes.

    74  */

    75 

    76 #define Buf_size (8 * 2*sizeof(char))

    77 /* Number of bits used within bi_buf. (bi_buf might be implemented on

    78  * more than 16 bits on some systems.)

    79  */

    80 

    81 /* ===========================================================================

    82  * Local data. These are initialized only once.

    83  */

    84 

    85 #define DIST_CODE_LEN  512 /* see definition of array dist_code below */

    86 

    87 #if defined(GEN_TREES_H) || !defined(STDC)

    88 /* non ANSI compilers may not accept trees.h */

    89 

    90 local ct_data static_ltree[L_CODES+2];

    91 /* The static literal tree. Since the bit lengths are imposed, there is no

    92  * need for the L_CODES extra codes used during heap construction. However

    93  * The codes 286 and 287 are needed to build a canonical tree (see _tr_init

    94  * below).

    95  */

    96 

    97 local ct_data static_dtree[D_CODES];

    98 /* The static distance tree. (Actually a trivial tree since all codes use

    99  * 5 bits.)

   100  */

   101 

   102 uch _dist_code[DIST_CODE_LEN];

   103 /* Distance codes. The first 256 values correspond to the distances

   104  * 3 .. 258, the last 256 values correspond to the top 8 bits of

   105  * the 15 bit distances.

   106  */

   107 

   108 uch _length_code[MAX_MATCH-MIN_MATCH+1];

   109 /* length code for each normalized match length (0 == MIN_MATCH) */

   110 

   111 local int base_length[LENGTH_CODES];

   112 /* First normalized length for each code (0 = MIN_MATCH) */

   113 

   114 local int base_dist[D_CODES];

   115 /* First normalized distance for each code (0 = distance of 1) */

   116 

   117 #else

   118 #  include "trees.h"

   119 #endif /* GEN_TREES_H */

   120 

   121 struct static_tree_desc_s {

   122     const ct_data *static_tree;  /* static tree or NULL */

   123     const intf *extra_bits;      /* extra bits for each code or NULL */

   124     int     extra_base;          /* base index for extra_bits */

   125     int     elems;               /* max number of elements in the tree */

   126     int     max_length;          /* max bit length for the codes */

   127 };

   128 

   129 local static_tree_desc  static_l_desc =

   130 {static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS};

   131 

   132 local static_tree_desc  static_d_desc =

   133 {static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS};

   134 

   135 local static_tree_desc  static_bl_desc =

   136 {(const ct_data *)0, extra_blbits, 0,   BL_CODES, MAX_BL_BITS};

   137 

   138 /* ===========================================================================

   139  * Local (static) routines in this file.

   140  */

   141 

   142 local void tr_static_init OF((void));

   143 local void init_block     OF((deflate_state *s));

   144 local void pqdownheap     OF((deflate_state *s, ct_data *tree, int k));

   145 local void gen_bitlen     OF((deflate_state *s, tree_desc *desc));

   146 local void gen_codes      OF((ct_data *tree, int max_code, ushf *bl_count));

   147 local void build_tree     OF((deflate_state *s, tree_desc *desc));

   148 local void scan_tree      OF((deflate_state *s, ct_data *tree, int max_code));

   149 local void send_tree      OF((deflate_state *s, ct_data *tree, int max_code));

   150 local int  build_bl_tree  OF((deflate_state *s));

   151 local void send_all_trees OF((deflate_state *s, int lcodes, int dcodes,

   152                               int blcodes));

   153 local void compress_block OF((deflate_state *s, ct_data *ltree,

   154                               ct_data *dtree));

   155 local void set_data_type  OF((deflate_state *s));

   156 local unsigned bi_reverse OF((unsigned value, int length));

   157 local void bi_windup      OF((deflate_state *s));

   158 local void bi_flush       OF((deflate_state *s));

   159 local void copy_block     OF((deflate_state *s, charf *buf, unsigned len,

   160                               int header));

   161 

   162 #ifdef GEN_TREES_H

   163 local void gen_trees_header OF((void));

   164 #endif

   165 

   166 #ifndef DEBUG

   167 #  define send_code(s, c, tree) send_bits(s, tree[c].Code, tree[c].Len)

   168    /* Send a code of the given tree. c and tree must not have side effects */

   169 

   170 #else /* DEBUG */

   171 #  define send_code(s, c, tree) \

   172      { if (z_verbose>2) fprintf(stderr,"\ncd %3d ",(c)); \

   173        send_bits(s, tree[c].Code, tree[c].Len); }

   174 #endif

   175 

   176 /* ===========================================================================

   177  * Output a short LSB first on the stream.

   178  * IN assertion: there is enough room in pendingBuf.

   179  */

   180 #define put_short(s, w) { \

   181     put_byte(s, (uch)((w) & 0xff)); \

   182     put_byte(s, (uch)((ush)(w) >> 8)); \

   183 }

   184 

   185 /* ===========================================================================

   186  * Send a value on a given number of bits.

   187  * IN assertion: length <= 16 and value fits in length bits.

   188  */

   189 #ifdef DEBUG

   190 local void send_bits      OF((deflate_state *s, int value, int length));

   191 

   192 local void send_bits(deflate_state *s, int value, int length)

   193 /* int value;   value to send */

   194 /* int length;  number of bits */

   195 

   196 {

   197     Tracevv((stderr," l %2d v %4x ", length, value));

   198     Assert(length > 0 && length <= 15, "invalid length");

   199     s->bits_sent += (ulg)length;

   200 

   201     /* If not enough room in bi_buf, use (valid) bits from bi_buf and

   202      * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))

   203      * unused bits in value.

   204      */

   205     if (s->bi_valid > (int)Buf_size - length) {

   206         s->bi_buf |= (value << s->bi_valid);

   207         put_short(s, s->bi_buf);

   208         s->bi_buf = (ush)value >> (Buf_size - s->bi_valid);

   209         s->bi_valid += length - Buf_size;

   210     } else {

   211         s->bi_buf |= value << s->bi_valid;

   212         s->bi_valid += length;

   213     }

   214 }

   215 #else /* !DEBUG */

   216 

   217 #define send_bits(s, value, length) \

   218 { int len = length;\

   219   if (s->bi_valid > (int)Buf_size - len) {\

   220     int val = value;\

   221     s->bi_buf |= (val << s->bi_valid);\

   222     put_short(s, s->bi_buf);\

   223     s->bi_buf = (ush)val >> (Buf_size - s->bi_valid);\

   224     s->bi_valid += len - Buf_size;\

   225   } else {\

   226     s->bi_buf |= (value) << s->bi_valid;\

   227     s->bi_valid += len;\

   228   }\

   229 }

   230 #endif /* DEBUG */

   231 

   232 

   233 #define MAX(a,b) (a >= b ? a : b)

   234 /* the arguments must not have side effects */

   235 

   236 /* ===========================================================================

   237  * Initialize the various 'constant' tables.

   238  */

   239 local void tr_static_init()

   240 {

   241 #if defined(GEN_TREES_H) || !defined(STDC)

   242     static int static_init_done = 0;

   243     int n;        /* iterates over tree elements */

   244     int bits;     /* bit counter */

   245     int length;   /* length value */

   246     int code;     /* code value */

   247     int dist;     /* distance index */

   248     ush bl_count[MAX_BITS+1];

   249     /* number of codes at each bit length for an optimal tree */

   250 

   251     if (static_init_done) return;

   252 

   253     /* For some embedded targets, global variables are not initialized: */

   254     static_l_desc.static_tree = static_ltree;

   255     static_l_desc.extra_bits = extra_lbits;

   256     static_d_desc.static_tree = static_dtree;

   257     static_d_desc.extra_bits = extra_dbits;

   258     static_bl_desc.extra_bits = extra_blbits;

   259 

   260     /* Initialize the mapping length (0..255) -> length code (0..28) */

   261     length = 0;

   262     for (code = 0; code < LENGTH_CODES-1; code++) {

   263         base_length[code] = length;

   264         for (n = 0; n < (1<<extra_lbits[code]); n++) {

   265             _length_code[length++] = (uch)code;

   266         }

   267     }

   268     Assert (length == 256, "tr_static_init: length != 256");

   269     /* Note that the length 255 (match length 258) can be represented

   270      * in two different ways: code 284 + 5 bits or code 285, so we

   271      * overwrite length_code[255] to use the best encoding:

   272      */

   273     _length_code[length-1] = (uch)code;

   274 

   275     /* Initialize the mapping dist (0..32K) -> dist code (0..29) */

   276     dist = 0;

   277     for (code = 0 ; code < 16; code++) {

   278         base_dist[code] = dist;

   279         for (n = 0; n < (1<<extra_dbits[code]); n++) {

   280             _dist_code[dist++] = (uch)code;

   281         }

   282     }

   283     Assert (dist == 256, "tr_static_init: dist != 256");

   284     dist >>= 7; /* from now on, all distances are divided by 128 */

   285     for ( ; code < D_CODES; code++) {

   286         base_dist[code] = dist << 7;

   287         for (n = 0; n < (1<<(extra_dbits[code]-7)); n++) {

   288             _dist_code[256 + dist++] = (uch)code;

   289         }

   290     }

   291     Assert (dist == 256, "tr_static_init: 256+dist != 512");

   292 

   293     /* Construct the codes of the static literal tree */

   294     for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;

   295     n = 0;

   296     while (n <= 143) static_ltree[n++].Len = 8, bl_count[8]++;

   297     while (n <= 255) static_ltree[n++].Len = 9, bl_count[9]++;

   298     while (n <= 279) static_ltree[n++].Len = 7, bl_count[7]++;

   299     while (n <= 287) static_ltree[n++].Len = 8, bl_count[8]++;

   300     /* Codes 286 and 287 do not exist, but we must include them in the

   301      * tree construction to get a canonical Huffman tree (longest code

   302      * all ones)

   303      */

   304     gen_codes((ct_data *)static_ltree, L_CODES+1, bl_count);

   305 

   306     /* The static distance tree is trivial: */

   307     for (n = 0; n < D_CODES; n++) {

   308         static_dtree[n].Len = 5;

   309         static_dtree[n].Code = bi_reverse((unsigned)n, 5);

   310     }

   311     static_init_done = 1;

   312 

   313 #  ifdef GEN_TREES_H

   314     gen_trees_header();

   315 #  endif

   316 #endif /* defined(GEN_TREES_H) || !defined(STDC) */

   317 }

   318 

   319 /* ===========================================================================

   320  * Genererate the file trees.h describing the static trees.

   321  */

   322 #ifdef GEN_TREES_H

   323 #  ifndef DEBUG

   324 #    include <stdio.h>

   325 #  endif

   326 

   327 #  define SEPARATOR(i, last, width) \

   328       ((i) == (last)? "\n};\n\n" :    \

   329        ((i) % (width) == (width)-1 ? ",\n" : ", "))

   330 

   331 void gen_trees_header()

   332 {

   333     FILE *header = fopen("trees.h", "w");

   334     int i;

   335 

   336     Assert (header != NULL, "Can't open trees.h");

   337     fprintf(header,

   338 	    "/* header created automatically with -DGEN_TREES_H */\n\n");

   339 

   340     fprintf(header, "local const ct_data static_ltree[L_CODES+2] = {\n");

   341     for (i = 0; i < L_CODES+2; i++) {

   342 	fprintf(header, "{{%3u},{%3u}}%s", static_ltree[i].Code,

   343 		static_ltree[i].Len, SEPARATOR(i, L_CODES+1, 5));

   344     }

   345 

   346     fprintf(header, "local const ct_data static_dtree[D_CODES] = {\n");

   347     for (i = 0; i < D_CODES; i++) {

   348 	fprintf(header, "{{%2u},{%2u}}%s", static_dtree[i].Code,

   349 		static_dtree[i].Len, SEPARATOR(i, D_CODES-1, 5));

   350     }

   351 

   352     fprintf(header, "const uch _dist_code[DIST_CODE_LEN] = {\n");

   353     for (i = 0; i < DIST_CODE_LEN; i++) {

   354 	fprintf(header, "%2u%s", _dist_code[i],

   355 		SEPARATOR(i, DIST_CODE_LEN-1, 20));

   356     }

   357 

   358     fprintf(header, "const uch _length_code[MAX_MATCH-MIN_MATCH+1]= {\n");

   359     for (i = 0; i < MAX_MATCH-MIN_MATCH+1; i++) {

   360 	fprintf(header, "%2u%s", _length_code[i],

   361 		SEPARATOR(i, MAX_MATCH-MIN_MATCH, 20));

   362     }

   363 

   364     fprintf(header, "local const int base_length[LENGTH_CODES] = {\n");

   365     for (i = 0; i < LENGTH_CODES; i++) {

   366 	fprintf(header, "%1u%s", base_length[i],

   367 		SEPARATOR(i, LENGTH_CODES-1, 20));

   368     }

   369 

   370     fprintf(header, "local const int base_dist[D_CODES] = {\n");

   371     for (i = 0; i < D_CODES; i++) {

   372 	fprintf(header, "%5u%s", base_dist[i],

   373 		SEPARATOR(i, D_CODES-1, 10));

   374     }

   375 

   376     fclose(header);

   377 }

   378 #endif /* GEN_TREES_H */

   379 

   380 /* ===========================================================================

   381  * Initialize the tree data structures for a new zlib stream.

   382  */

   383 void _tr_init(deflate_state *s)

   384 {

   385     tr_static_init();

   386 

   387     s->l_desc.dyn_tree = s->dyn_ltree;

   388     s->l_desc.stat_desc = &static_l_desc;

   389 

   390     s->d_desc.dyn_tree = s->dyn_dtree;

   391     s->d_desc.stat_desc = &static_d_desc;

   392 

   393     s->bl_desc.dyn_tree = s->bl_tree;

   394     s->bl_desc.stat_desc = &static_bl_desc;

   395 

   396     s->bi_buf = 0;

   397     s->bi_valid = 0;

   398     s->last_eob_len = 8; /* enough lookahead for inflate */

   399 #ifdef DEBUG

   400     s->compressed_len = 0L;

   401     s->bits_sent = 0L;

   402 #endif

   403 

   404     /* Initialize the first block of the first file: */

   405     init_block(s);

   406 }

   407 

   408 /* ===========================================================================

   409  * Initialize a new block.

   410  */

   411 local void init_block(deflate_state *s)

   412 {

   413     int n; /* iterates over tree elements */

   414 

   415     /* Initialize the trees. */

   416     for (n = 0; n < L_CODES;  n++) s->dyn_ltree[n].Freq = 0;

   417     for (n = 0; n < D_CODES;  n++) s->dyn_dtree[n].Freq = 0;

   418     for (n = 0; n < BL_CODES; n++) s->bl_tree[n].Freq = 0;

   419 

   420     s->dyn_ltree[END_BLOCK].Freq = 1;

   421     s->opt_len = s->static_len = 0L;

   422     s->last_lit = s->matches = 0;

   423 }

   424 

   425 #define SMALLEST 1

   426 /* Index within the heap array of least frequent node in the Huffman tree */

   427 

   428 

   429 /* ===========================================================================

   430  * Remove the smallest element from the heap and recreate the heap with

   431  * one less element. Updates heap and heap_len.

   432  */

   433 #define pqremove(s, tree, top) \

   434 {\

   435     top = s->heap[SMALLEST]; \

   436     s->heap[SMALLEST] = s->heap[s->heap_len--]; \

   437     pqdownheap(s, tree, SMALLEST); \

   438 }

   439 

   440 /* ===========================================================================

   441  * Compares to subtrees, using the tree depth as tie breaker when

   442  * the subtrees have equal frequency. This minimizes the worst case length.

   443  */

   444 #define smaller(tree, n, m, depth) \

   445    (tree[n].Freq < tree[m].Freq || \

   446    (tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))

   447 

   448 /* ===========================================================================

   449  * Restore the heap property by moving down the tree starting at node k,

   450  * exchanging a node with the smallest of its two sons if necessary, stopping

   451  * when the heap property is re-established (each father smaller than its

   452  * two sons).

   453  */

   454 local void pqdownheap(deflate_state *s, ct_data *tree, int k)

   455 /* ct_data *tree;      the tree to restore */

   456 /* int k;              node to move down */

   457 {

   458     int v = s->heap[k];

   459     int j = k << 1;  /* left son of k */

   460     while (j <= s->heap_len) {

   461         /* Set j to the smallest of the two sons: */

   462         if (j < s->heap_len &&

   463             smaller(tree, s->heap[j+1], s->heap[j], s->depth)) {

   464             j++;

   465         }

   466         /* Exit if v is smaller than both sons */

   467         if (smaller(tree, v, s->heap[j], s->depth)) break;

   468 

   469         /* Exchange v with the smallest son */

   470         s->heap[k] = s->heap[j];  k = j;

   471 

   472         /* And continue down the tree, setting j to the left son of k */

   473         j <<= 1;

   474     }

   475     s->heap[k] = v;

   476 }

   477 

   478 /* ===========================================================================

   479  * Compute the optimal bit lengths for a tree and update the total bit length

   480  * for the current block.

   481  * IN assertion: the fields freq and dad are set, heap[heap_max] and

   482  *    above are the tree nodes sorted by increasing frequency.

   483  * OUT assertions: the field len is set to the optimal bit length, the

   484  *     array bl_count contains the frequencies for each bit length.

   485  *     The length opt_len is updated; static_len is also updated if stree is

   486  *     not null.

   487  */

   488 local void gen_bitlen(deflate_state *s, tree_desc *desc)

   489 /* tree_desc *desc;     the tree descriptor */

   490 {

   491     ct_data *tree        = desc->dyn_tree;

   492     int max_code         = desc->max_code;

   493     const ct_data *stree = desc->stat_desc->static_tree;

   494     const intf *extra    = desc->stat_desc->extra_bits;

   495     int base             = desc->stat_desc->extra_base;

   496     int max_length       = desc->stat_desc->max_length;

   497     int h;              /* heap index */

   498     int n, m;           /* iterate over the tree elements */

   499     int bits;           /* bit length */

   500     int xbits;          /* extra bits */

   501     ush f;              /* frequency */

   502     int overflow = 0;   /* number of elements with bit length too large */

   503 

   504     for (bits = 0; bits <= MAX_BITS; bits++) s->bl_count[bits] = 0;

   505 

   506     /* In a first pass, compute the optimal bit lengths (which may

   507      * overflow in the case of the bit length tree).

   508      */

   509     tree[s->heap[s->heap_max]].Len = 0; /* root of the heap */

   510 

   511     for (h = s->heap_max+1; h < HEAP_SIZE; h++) {

   512         n = s->heap[h];

   513         bits = tree[tree[n].Dad].Len + 1;

   514         if (bits > max_length) bits = max_length, overflow++;

   515         tree[n].Len = (ush)bits;

   516         /* We overwrite tree[n].Dad which is no longer needed */

   517 

   518         if (n > max_code) continue; /* not a leaf node */

   519 

   520         s->bl_count[bits]++;

   521         xbits = 0;

   522         if (n >= base) xbits = extra[n-base];

   523         f = tree[n].Freq;

   524         s->opt_len += (ulg)f * (bits + xbits);

   525         if (stree) s->static_len += (ulg)f * (stree[n].Len + xbits);

   526     }

   527     if (overflow == 0) return;

   528 

   529     Trace((stderr,"\nbit length overflow\n"));

   530     /* This happens for example on obj2 and pic of the Calgary corpus */

   531 

   532     /* Find the first bit length which could increase: */

   533     do {

   534         bits = max_length-1;

   535         while (s->bl_count[bits] == 0) bits--;

   536         s->bl_count[bits]--;      /* move one leaf down the tree */

   537         s->bl_count[bits+1] += 2; /* move one overflow item as its brother */

   538         s->bl_count[max_length]--;

   539         /* The brother of the overflow item also moves one step up,

   540          * but this does not affect bl_count[max_length]

   541          */

   542         overflow -= 2;

   543     } while (overflow > 0);

   544 

   545     /* Now recompute all bit lengths, scanning in increasing frequency.

   546      * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all

   547      * lengths instead of fixing only the wrong ones. This idea is taken

   548      * from 'ar' written by Haruhiko Okumura.)

   549      */

   550     for (bits = max_length; bits != 0; bits--) {

   551         n = s->bl_count[bits];

   552         while (n != 0) {

   553             m = s->heap[--h];

   554             if (m > max_code) continue;

   555             if (tree[m].Len != (unsigned) bits) {

   556                 Trace((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));

   557                 s->opt_len += ((long)bits - (long)tree[m].Len)

   558                               *(long)tree[m].Freq;

   559                 tree[m].Len = (ush)bits;

   560             }

   561             n--;

   562         }

   563     }

   564 }

   565 

   566 /* ===========================================================================

   567  * Generate the codes for a given tree and bit counts (which need not be

   568  * optimal).

   569  * IN assertion: the array bl_count contains the bit length statistics for

   570  * the given tree and the field len is set for all tree elements.

   571  * OUT assertion: the field code is set for all tree elements of non

   572  *     zero code length.

   573  */

   574 local void gen_codes (ct_data *tree, int max_code, ushf *bl_count)

   575 /* ct_data *tree;              the tree to decorate */

   576 /* int max_code;               largest code with non zero frequency */

   577 /* ushf *bl_count;             number of codes at each bit length */

   578 {

   579     ush next_code[MAX_BITS+1]; /* next code value for each bit length */

   580     ush code = 0;              /* running code value */

   581     int bits;                  /* bit index */

   582     int n;                     /* code index */

   583 

   584     /* The distribution counts are first used to generate the code values

   585      * without bit reversal.

   586      */

   587     for (bits = 1; bits <= MAX_BITS; bits++) {

   588         next_code[bits] = code = (code + bl_count[bits-1]) << 1;

   589     }

   590     /* Check that the bit counts in bl_count are consistent. The last code

   591      * must be all ones.

   592      */

   593     Assert (code + bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1,

   594             "inconsistent bit counts");

   595     Tracev((stderr,"\ngen_codes: max_code %d ", max_code));

   596 

   597     for (n = 0;  n <= max_code; n++) {

   598         int len = tree[n].Len;

   599         if (len == 0) continue;

   600         /* Now reverse the bits */

   601         tree[n].Code = bi_reverse(next_code[len]++, len);

   602 

   603         Tracecv(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",

   604              n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len]-1));

   605     }

   606 }

   607 

   608 /* ===========================================================================

   609  * Construct one Huffman tree and assigns the code bit strings and lengths.

   610  * Update the total bit length for the current block.

   611  * IN assertion: the field freq is set for all tree elements.

   612  * OUT assertions: the fields len and code are set to the optimal bit length

   613  *     and corresponding code. The length opt_len is updated; static_len is

   614  *     also updated if stree is not null. The field max_code is set.

   615  */

   616 local void build_tree(deflate_state *s, tree_desc *desc)

   617 /* tree_desc *desc;        the tree descriptor */

   618 {

   619     ct_data *tree         = desc->dyn_tree;

   620     const ct_data *stree  = desc->stat_desc->static_tree;

   621     int elems             = desc->stat_desc->elems;

   622     int n, m;          /* iterate over heap elements */

   623     int max_code = -1; /* largest code with non zero frequency */

   624     int node;          /* new node being created */

   625 

   626     /* Construct the initial heap, with least frequent element in

   627      * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].

   628      * heap[0] is not used.

   629      */

   630     s->heap_len = 0, s->heap_max = HEAP_SIZE;

   631 

   632     for (n = 0; n < elems; n++) {

   633         if (tree[n].Freq != 0) {

   634             s->heap[++(s->heap_len)] = max_code = n;

   635             s->depth[n] = 0;

   636         } else {

   637             tree[n].Len = 0;

   638         }

   639     }

   640 

   641     /* The pkzip format requires that at least one distance code exists,

   642      * and that at least one bit should be sent even if there is only one

   643      * possible code. So to avoid special checks later on we force at least

   644      * two codes of non zero frequency.

   645      */

   646     while (s->heap_len < 2) {

   647         node = s->heap[++(s->heap_len)] = (max_code < 2 ? ++max_code : 0);

   648         tree[node].Freq = 1;

   649         s->depth[node] = 0;

   650         s->opt_len--; if (stree) s->static_len -= stree[node].Len;

   651         /* node is 0 or 1 so it does not have extra bits */

   652     }

   653     desc->max_code = max_code;

   654 

   655     /* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,

   656      * establish sub-heaps of increasing lengths:

   657      */

   658     for (n = s->heap_len/2; n >= 1; n--) pqdownheap(s, tree, n);

   659 

   660     /* Construct the Huffman tree by repeatedly combining the least two

   661      * frequent nodes.

   662      */

   663     node = elems;              /* next internal node of the tree */

   664     do {

   665         pqremove(s, tree, n);  /* n = node of least frequency */

   666         m = s->heap[SMALLEST]; /* m = node of next least frequency */

   667 

   668         s->heap[--(s->heap_max)] = n; /* keep the nodes sorted by frequency */

   669         s->heap[--(s->heap_max)] = m;

   670 

   671         /* Create a new node father of n and m */

   672         tree[node].Freq = tree[n].Freq + tree[m].Freq;

   673         s->depth[node] = (uch) (MAX(s->depth[n], s->depth[m]) + 1);

   674         tree[n].Dad = tree[m].Dad = (ush)node;

   675 #ifdef DUMP_BL_TREE

   676         if (tree == s->bl_tree) {

   677             fprintf(stderr,"\nnode %d(%d), sons %d(%d) %d(%d)",

   678                     node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq);

   679         }

   680 #endif

   681         /* and insert the new node in the heap */

   682         s->heap[SMALLEST] = node++;

   683         pqdownheap(s, tree, SMALLEST);

   684 

   685     } while (s->heap_len >= 2);

   686 

   687     s->heap[--(s->heap_max)] = s->heap[SMALLEST];

   688 

   689     /* At this point, the fields freq and dad are set. We can now

   690      * generate the bit lengths.

   691      */

   692     gen_bitlen(s, (tree_desc *)desc);

   693 

   694     /* The field len is now set, we can generate the bit codes */

   695     gen_codes ((ct_data *)tree, max_code, s->bl_count);

   696 }

   697 

   698 /* ===========================================================================

   699  * Scan a literal or distance tree to determine the frequencies of the codes

   700  * in the bit length tree.

   701  */

   702 local void scan_tree (deflate_state *s, ct_data *tree, int max_code)

   703 /* ct_data *tree;         the tree to be scanned */

   704 /* int max_code;          and its largest code of non zero frequency */

   705 {

   706     int n;                     /* iterates over all tree elements */

   707     int prevlen = -1;          /* last emitted length */

   708     int curlen;                /* length of current code */

   709     int nextlen = tree[0].Len; /* length of next code */

   710     int count = 0;             /* repeat count of the current code */

   711     int max_count = 7;         /* max repeat count */

   712     int min_count = 4;         /* min repeat count */

   713 

   714     if (nextlen == 0) max_count = 138, min_count = 3;

   715     tree[max_code+1].Len = (ush)0xffff; /* guard */

   716 

   717     for (n = 0; n <= max_code; n++) {

   718         curlen = nextlen; nextlen = tree[n+1].Len;

   719         if (++count < max_count && curlen == nextlen) {

   720             continue;

   721         } else if (count < min_count) {

   722             s->bl_tree[curlen].Freq += count;

   723         } else if (curlen != 0) {

   724             if (curlen != prevlen) s->bl_tree[curlen].Freq++;

   725             s->bl_tree[REP_3_6].Freq++;

   726         } else if (count <= 10) {

   727             s->bl_tree[REPZ_3_10].Freq++;

   728         } else {

   729             s->bl_tree[REPZ_11_138].Freq++;

   730         }

   731         count = 0; prevlen = curlen;

   732         if (nextlen == 0) {

   733             max_count = 138, min_count = 3;

   734         } else if (curlen == nextlen) {

   735             max_count = 6, min_count = 3;

   736         } else {

   737             max_count = 7, min_count = 4;

   738         }

   739     }

   740 }

   741 

   742 /* ===========================================================================

   743  * Send a literal or distance tree in compressed form, using the codes in

   744  * bl_tree.

   745  */

   746 local void send_tree (deflate_state *s, ct_data *tree, int max_code)

   747 /* ct_data *tree;        the tree to be scanned */

   748 /* int max_code;         and its largest code of non zero frequency */

   749 {

   750     int n;                     /* iterates over all tree elements */

   751     int prevlen = -1;          /* last emitted length */

   752     int curlen;                /* length of current code */

   753     int nextlen = tree[0].Len; /* length of next code */

   754     int count = 0;             /* repeat count of the current code */

   755     int max_count = 7;         /* max repeat count */

   756     int min_count = 4;         /* min repeat count */

   757 

   758     /* tree[max_code+1].Len = -1; */  /* guard already set */

   759     if (nextlen == 0) max_count = 138, min_count = 3;

   760 

   761     for (n = 0; n <= max_code; n++) {

   762         curlen = nextlen; nextlen = tree[n+1].Len;

   763         if (++count < max_count && curlen == nextlen) {

   764             continue;

   765         } else if (count < min_count) {

   766             do { send_code(s, curlen, s->bl_tree); } while (--count != 0);

   767 

   768         } else if (curlen != 0) {

   769             if (curlen != prevlen) {

   770                 send_code(s, curlen, s->bl_tree); count--;

   771             }

   772             Assert(count >= 3 && count <= 6, " 3_6?");

   773             send_code(s, REP_3_6, s->bl_tree); send_bits(s, count-3, 2);

   774 

   775         } else if (count <= 10) {

   776             send_code(s, REPZ_3_10, s->bl_tree); send_bits(s, count-3, 3);

   777 

   778         } else {

   779             send_code(s, REPZ_11_138, s->bl_tree); send_bits(s, count-11, 7);

   780         }

   781         count = 0; prevlen = curlen;

   782         if (nextlen == 0) {

   783             max_count = 138, min_count = 3;

   784         } else if (curlen == nextlen) {

   785             max_count = 6, min_count = 3;

   786         } else {

   787             max_count = 7, min_count = 4;

   788         }

   789     }

   790 }

   791 

   792 /* ===========================================================================

   793  * Construct the Huffman tree for the bit lengths and return the index in

   794  * bl_order of the last bit length code to send.

   795  */

   796 local int build_bl_tree(deflate_state *s)

   797 {

   798     int max_blindex;  /* index of last bit length code of non zero freq */

   799 

   800     /* Determine the bit length frequencies for literal and distance trees */

   801     scan_tree(s, (ct_data *)s->dyn_ltree, s->l_desc.max_code);

   802     scan_tree(s, (ct_data *)s->dyn_dtree, s->d_desc.max_code);

   803 

   804     /* Build the bit length tree: */

   805     build_tree(s, (tree_desc *)(&(s->bl_desc)));

   806     /* opt_len now includes the length of the tree representations, except

   807      * the lengths of the bit lengths codes and the 5+5+4 bits for the counts.

   808      */

   809 

   810     /* Determine the number of bit length codes to send. The pkzip format

   811      * requires that at least 4 bit length codes be sent. (appnote.txt says

   812      * 3 but the actual value used is 4.)

   813      */

   814     for (max_blindex = BL_CODES-1; max_blindex >= 3; max_blindex--) {

   815         if (s->bl_tree[bl_order[max_blindex]].Len != 0) break;

   816     }

   817     /* Update opt_len to include the bit length tree and counts */

   818     s->opt_len += 3*(max_blindex+1) + 5+5+4;

   819     Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld",

   820             s->opt_len, s->static_len));

   821 

   822     return max_blindex;

   823 }

   824 

   825 /* ===========================================================================

   826  * Send the header for a block using dynamic Huffman trees: the counts, the

   827  * lengths of the bit length codes, the literal tree and the distance tree.

   828  * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.

   829  */

   830 local void send_all_trees(deflate_state *s, int lcodes, int dcodes, int blcodes)

   831 /* int lcodes, dcodes, blcodes;          number of codes for each tree */

   832 {

   833     int rank;                    /* index in bl_order */

   834 

   835     Assert (lcodes >= 257 && dcodes >= 1 && blcodes >= 4, "not enough codes");

   836     Assert (lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,

   837             "too many codes");

   838     Tracev((stderr, "\nbl counts: "));

   839     send_bits(s, lcodes-257, 5); /* not +255 as stated in appnote.txt */

   840     send_bits(s, dcodes-1,   5);

   841     send_bits(s, blcodes-4,  4); /* not -3 as stated in appnote.txt */

   842     for (rank = 0; rank < blcodes; rank++) {

   843         Tracev((stderr, "\nbl code %2d ", bl_order[rank]));

   844         send_bits(s, s->bl_tree[bl_order[rank]].Len, 3);

   845     }

   846     Tracev((stderr, "\nbl tree: sent %ld", s->bits_sent));

   847 

   848     send_tree(s, (ct_data *)s->dyn_ltree, lcodes-1); /* literal tree */

   849     Tracev((stderr, "\nlit tree: sent %ld", s->bits_sent));

   850 

   851     send_tree(s, (ct_data *)s->dyn_dtree, dcodes-1); /* distance tree */

   852     Tracev((stderr, "\ndist tree: sent %ld", s->bits_sent));

   853 }

   854 

   855 /* ===========================================================================

   856  * Send a stored block

   857  */

   858 void _tr_stored_block(deflate_state *s, charf *buf, ulg stored_len, int eof)

   859 /* charf *buf;        input block */

   860 /* ulg stored_len;    length of input block */

   861 /* int eof;           true if this is the last block for a file */

   862 {

   863     send_bits(s, (STORED_BLOCK<<1)+eof, 3);  /* send block type */

   864 #ifdef DEBUG

   865     s->compressed_len = (s->compressed_len + 3 + 7) & (ulg)~7L;

   866     s->compressed_len += (stored_len + 4) << 3;

   867 #endif

   868     copy_block(s, buf, (unsigned)stored_len, 1); /* with header */

   869 }

   870 

   871 /* ===========================================================================

   872  * Send one empty static block to give enough lookahead for inflate.

   873  * This takes 10 bits, of which 7 may remain in the bit buffer.

   874  * The current inflate code requires 9 bits of lookahead. If the

   875  * last two codes for the previous block (real code plus EOB) were coded

   876  * on 5 bits or less, inflate may have only 5+3 bits of lookahead to decode

   877  * the last real code. In this case we send two empty static blocks instead

   878  * of one. (There are no problems if the previous block is stored or fixed.)

   879  * To simplify the code, we assume the worst case of last real code encoded

   880  * on one bit only.

   881  */

   882 void _tr_align(deflate_state *s)

   883 {

   884     send_bits(s, STATIC_TREES<<1, 3);

   885     send_code(s, END_BLOCK, static_ltree);

   886 #ifdef DEBUG

   887     s->compressed_len += 10L; /* 3 for block type, 7 for EOB */

   888 #endif

   889     bi_flush(s);

   890     /* Of the 10 bits for the empty block, we have already sent

   891      * (10 - bi_valid) bits. The lookahead for the last real code (before

   892      * the EOB of the previous block) was thus at least one plus the length

   893      * of the EOB plus what we have just sent of the empty static block.

   894      */

   895     if (1 + s->last_eob_len + 10 - s->bi_valid < 9) {

   896         send_bits(s, STATIC_TREES<<1, 3);

   897         send_code(s, END_BLOCK, static_ltree);

   898 #ifdef DEBUG

   899         s->compressed_len += 10L;

   900 #endif

   901         bi_flush(s);

   902     }

   903     s->last_eob_len = 7;

   904 }

   905 

   906 /* ===========================================================================

   907  * Determine the best encoding for the current block: dynamic trees, static

   908  * trees or store, and output the encoded block to the zip file.

   909  */

   910 void _tr_flush_block(deflate_state *s, charf *buf, ulg stored_len, int eof)

   911 /* charf *buf;            input block, or NULL if too old */

   912 /* ulg stored_len;        length of input block */

   913 /* int eof;               true if this is the last block for a file */

   914 {

   915     ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */

   916     int max_blindex = 0;  /* index of last bit length code of non zero freq */

   917 

   918     /* Build the Huffman trees unless a stored block is forced */

   919     if (s->level > 0) {

   920 

   921 	 /* Check if the file is ascii or binary */

   922 	if (s->data_type == Z_UNKNOWN) set_data_type(s);

   923 

   924 	/* Construct the literal and distance trees */

   925 	build_tree(s, (tree_desc *)(&(s->l_desc)));

   926 	Tracev((stderr, "\nlit data: dyn %ld, stat %ld", s->opt_len,

   927 		s->static_len));

   928 

   929 	build_tree(s, (tree_desc *)(&(s->d_desc)));

   930 	Tracev((stderr, "\ndist data: dyn %ld, stat %ld", s->opt_len,

   931 		s->static_len));

   932 	/* At this point, opt_len and static_len are the total bit lengths of

   933 	 * the compressed block data, excluding the tree representations.

   934 	 */

   935 

   936 	/* Build the bit length tree for the above two trees, and get the index

   937 	 * in bl_order of the last bit length code to send.

   938 	 */

   939 	max_blindex = build_bl_tree(s);

   940 

   941 	/* Determine the best encoding. Compute first the block length in bytes*/

   942 	opt_lenb = (s->opt_len+3+7)>>3;

   943 	static_lenb = (s->static_len+3+7)>>3;

   944 

   945 	Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ",

   946 		opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len,

   947 		s->last_lit));

   948 

   949 	if (static_lenb <= opt_lenb) opt_lenb = static_lenb;

   950 

   951     } else {

   952         Assert(buf != (char*)0, "lost buf");

   953 	opt_lenb = static_lenb = stored_len + 5; /* force a stored block */

   954     }

   955 

   956 #ifdef FORCE_STORED

   957     if (buf != (char*)0) { /* force stored block */

   958 #else

   959     if (stored_len+4 <= opt_lenb && buf != (char*)0) {

   960                        /* 4: two words for the lengths */

   961 #endif

   962         /* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.

   963          * Otherwise we can't have processed more than WSIZE input bytes since

   964          * the last block flush, because compression would have been

   965          * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to

   966          * transform a block into a stored block.

   967          */

   968         _tr_stored_block(s, buf, stored_len, eof);

   969 

   970 #ifdef FORCE_STATIC

   971     } else if (static_lenb >= 0) { /* force static trees */

   972 #else

   973     } else if (static_lenb == opt_lenb) {

   974 #endif

   975         send_bits(s, (STATIC_TREES<<1)+eof, 3);

   976         compress_block(s, (ct_data *)static_ltree, (ct_data *)static_dtree);

   977 #ifdef DEBUG

   978         s->compressed_len += 3 + s->static_len;

   979 #endif

   980     } else {

   981         send_bits(s, (DYN_TREES<<1)+eof, 3);

   982         send_all_trees(s, s->l_desc.max_code+1, s->d_desc.max_code+1,

   983                        max_blindex+1);

   984         compress_block(s, (ct_data *)s->dyn_ltree, (ct_data *)s->dyn_dtree);

   985 #ifdef DEBUG

   986         s->compressed_len += 3 + s->opt_len;

   987 #endif

   988     }

   989     Assert (s->compressed_len == s->bits_sent, "bad compressed size");

   990     /* The above check is made mod 2^32, for files larger than 512 MB

   991      * and uLong implemented on 32 bits.

   992      */

   993     init_block(s);

   994 

   995     if (eof) {

   996         bi_windup(s);

   997 #ifdef DEBUG

   998         s->compressed_len += 7;  /* align on byte boundary */

   999 #endif

  1000     }

  1001     Tracev((stderr,"\ncomprlen %lu(%lu) ", s->compressed_len>>3,

  1002            s->compressed_len-7*eof));

  1003 }

  1004 

  1005 /* ===========================================================================

  1006  * Save the match info and tally the frequency counts. Return true if

  1007  * the current block must be flushed.

  1008  */

  1009 int _tr_tally (deflate_state *s, unsigned dist, unsigned lc)

  1010 /* unsigned dist;      distance of matched string */

  1011 /* unsigned lc;        match length-MIN_MATCH or unmatched char (if dist==0) */

  1012 {

  1013     s->d_buf[s->last_lit] = (ush)dist;

  1014     s->l_buf[s->last_lit++] = (uch)lc;

  1015     if (dist == 0) {

  1016         /* lc is the unmatched char */

  1017         s->dyn_ltree[lc].Freq++;

  1018     } else {

  1019         s->matches++;

  1020         /* Here, lc is the match length - MIN_MATCH */

  1021         dist--;             /* dist = match distance - 1 */

  1022         Assert((ush)dist < (ush)MAX_DIST(s) &&

  1023                (ush)lc <= (ush)(MAX_MATCH-MIN_MATCH) &&

  1024                (ush)d_code(dist) < (ush)D_CODES,  "_tr_tally: bad match");

  1025 

  1026         s->dyn_ltree[_length_code[lc]+LITERALS+1].Freq++;

  1027         s->dyn_dtree[d_code(dist)].Freq++;

  1028     }

  1029 

  1030 #ifdef TRUNCATE_BLOCK

  1031     /* Try to guess if it is profitable to stop the current block here */

  1032     if ((s->last_lit & 0x1fff) == 0 && s->level > 2) {

  1033         /* Compute an upper bound for the compressed length */

  1034         ulg out_length = (ulg)s->last_lit*8L;

  1035         ulg in_length = (ulg)((long)s->strstart - s->block_start);

  1036         int dcode;

  1037         for (dcode = 0; dcode < D_CODES; dcode++) {

  1038             out_length += (ulg)s->dyn_dtree[dcode].Freq *

  1039                 (5L+extra_dbits[dcode]);

  1040         }

  1041         out_length >>= 3;

  1042         Tracev((stderr,"\nlast_lit %u, in %ld, out ~%ld(%ld%%) ",

  1043                s->last_lit, in_length, out_length,

  1044                100L - out_length*100L/in_length));

  1045         if (s->matches < s->last_lit/2 && out_length < in_length/2) return 1;

  1046     }

  1047 #endif

  1048     return (s->last_lit == s->lit_bufsize-1);

  1049     /* We avoid equality with lit_bufsize because of wraparound at 64K

  1050      * on 16 bit machines and because stored blocks are restricted to

  1051      * 64K-1 bytes.

  1052      */

  1053 }

  1054 

  1055 /* ===========================================================================

  1056  * Send the block data compressed using the given Huffman trees

  1057  */

  1058 local void compress_block(deflate_state *s, ct_data *ltree, ct_data *dtree)

  1059 {

  1060     unsigned dist;      /* distance of matched string */

  1061     int lc;             /* match length or unmatched char (if dist == 0) */

  1062     unsigned lx = 0;    /* running index in l_buf */

  1063     unsigned code;      /* the code to send */

  1064     int extra;          /* number of extra bits to send */

  1065 

  1066     if (s->last_lit != 0) do {

  1067         dist = s->d_buf[lx];

  1068         lc = s->l_buf[lx++];

  1069         if (dist == 0) {

  1070             send_code(s, lc, ltree); /* send a literal byte */

  1071             Tracecv(isgraph(lc), (stderr," '%c' ", lc));

  1072         } else {

  1073             /* Here, lc is the match length - MIN_MATCH */

  1074             code = _length_code[lc];

  1075             send_code(s, code+LITERALS+1, ltree); /* send the length code */

  1076             extra = extra_lbits[code];

  1077             if (extra != 0) {

  1078                 lc -= base_length[code];

  1079                 send_bits(s, lc, extra);       /* send the extra length bits */

  1080             }

  1081             dist--; /* dist is now the match distance - 1 */

  1082             code = d_code(dist);

  1083             Assert (code < D_CODES, "bad d_code");

  1084 

  1085             send_code(s, code, dtree);       /* send the distance code */

  1086             extra = extra_dbits[code];

  1087             if (extra != 0) {

  1088                 dist -= base_dist[code];

  1089                 send_bits(s, dist, extra);   /* send the extra distance bits */

  1090             }

  1091         } /* literal or match pair ? */

  1092 

  1093         /* Check that the overlay between pending_buf and d_buf+l_buf is ok: */

  1094         Assert(s->pending < s->lit_bufsize + 2*lx, "pendingBuf overflow");

  1095 

  1096     } while (lx < s->last_lit);

  1097 

  1098     send_code(s, END_BLOCK, ltree);

  1099     s->last_eob_len = ltree[END_BLOCK].Len;

  1100 }

  1101 

  1102 /* ===========================================================================

  1103  * Set the data type to ASCII or BINARY, using a crude approximation:

  1104  * binary if more than 20% of the bytes are <= 6 or >= 128, ascii otherwise.

  1105  * IN assertion: the fields freq of dyn_ltree are set and the total of all

  1106  * frequencies does not exceed 64K (to fit in an int on 16 bit machines).

  1107  */

  1108 local void set_data_type(deflate_state *s)

  1109 {

  1110     int n = 0;

  1111     unsigned ascii_freq = 0;

  1112     unsigned bin_freq = 0;

  1113     while (n < 7)        bin_freq += s->dyn_ltree[n++].Freq;

  1114     while (n < 128)    ascii_freq += s->dyn_ltree[n++].Freq;

  1115     while (n < LITERALS) bin_freq += s->dyn_ltree[n++].Freq;

  1116     s->data_type = (Byte)(bin_freq > (ascii_freq >> 2) ? Z_BINARY : Z_ASCII);

  1117 }

  1118 

  1119 /* ===========================================================================

  1120  * Reverse the first len bits of a code, using straightforward code (a faster

  1121  * method would use a table)

  1122  * IN assertion: 1 <= len <= 15

  1123  */

  1124 local unsigned bi_reverse(unsigned code, int len)

  1125 /* unsigned code;      the value to invert */

  1126 /* int len;            its bit length */

  1127 {

  1128     register unsigned res = 0;

  1129     do {

  1130         res |= code & 1;

  1131         code >>= 1, res <<= 1;

  1132     } while (--len > 0);

  1133     return res >> 1;

  1134 }

  1135