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      1 /* trees.c -- output deflated data using Huffman coding
      2  * Copyright (C) 1995-2010 Jean-loup Gailly
      3  * detect_data_type() function provided freely by Cosmin Truta, 2006
      4  * For conditions of distribution and use, see copyright notice in zlib.h
      5  */
      6 
      7 /*
      8  *  ALGORITHM
      9  *
     10  *      The "deflation" process uses several Huffman trees. The more
     11  *      common source values are represented by shorter bit sequences.
     12  *
     13  *      Each code tree is stored in a compressed form which is itself
     14  * a Huffman encoding of the lengths of all the code strings (in
     15  * ascending order by source values).  The actual code strings are
     16  * reconstructed from the lengths in the inflate process, as described
     17  * in the deflate specification.
     18  *
     19  *  REFERENCES
     20  *
     21  *      Deutsch, L.P.,"'Deflate' Compressed Data Format Specification".
     22  *      Available in ftp.uu.net:/pub/archiving/zip/doc/deflate-1.1.doc
     23  *
     24  *      Storer, James A.
     25  *          Data Compression:  Methods and Theory, pp. 49-50.
     26  *          Computer Science Press, 1988.  ISBN 0-7167-8156-5.
     27  *
     28  *      Sedgewick, R.
     29  *          Algorithms, p290.
     30  *          Addison-Wesley, 1983. ISBN 0-201-06672-6.
     31  */
     32 
     33 /* @(#) $Id$ */
     34 
     35 /* #define GEN_TREES_H */
     36 
     37 #include "deflate.h"
     38 
     39 #ifdef DEBUG_ZLIB
     40 #  include <ctype.h>
     41 #endif
     42 
     43 /* ===========================================================================
     44  * Constants
     45  */
     46 
     47 #define MAX_BL_BITS 7
     48 /* Bit length codes must not exceed MAX_BL_BITS bits */
     49 
     50 #define END_BLOCK 256
     51 /* end of block literal code */
     52 
     53 #define REP_3_6      16
     54 /* repeat previous bit length 3-6 times (2 bits of repeat count) */
     55 
     56 #define REPZ_3_10    17
     57 /* repeat a zero length 3-10 times  (3 bits of repeat count) */
     58 
     59 #define REPZ_11_138  18
     60 /* repeat a zero length 11-138 times  (7 bits of repeat count) */
     61 
     62 local const int extra_lbits[LENGTH_CODES] /* extra bits for each length code */
     63    = {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};
     64 
     65 local const int extra_dbits[D_CODES] /* extra bits for each distance code */
     66    = {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};
     67 
     68 local const int extra_blbits[BL_CODES]/* extra bits for each bit length code */
     69    = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7};
     70 
     71 local const uch bl_order[BL_CODES]
     72    = {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};
     73 /* The lengths of the bit length codes are sent in order of decreasing
     74  * probability, to avoid transmitting the lengths for unused bit length codes.
     75  */
     76 
     77 #define Buf_size (8 * 2*sizeof(char))
     78 /* Number of bits used within bi_buf. (bi_buf might be implemented on
     79  * more than 16 bits on some systems.)
     80  */
     81 
     82 /* ===========================================================================
     83  * Local data. These are initialized only once.
     84  */
     85 
     86 #define DIST_CODE_LEN  512 /* see definition of array dist_code below */
     87 
     88 #if defined(GEN_TREES_H) || !defined(STDC)
     89 /* non ANSI compilers may not accept trees.h */
     90 
     91 local ct_data static_ltree[L_CODES+2];
     92 /* The static literal tree. Since the bit lengths are imposed, there is no
     93  * need for the L_CODES extra codes used during heap construction. However
     94  * The codes 286 and 287 are needed to build a canonical tree (see _tr_init
     95  * below).
     96  */
     97 
     98 local ct_data static_dtree[D_CODES];
     99 /* The static distance tree. (Actually a trivial tree since all codes use
    100  * 5 bits.)
    101  */
    102 
    103 uch _dist_code[DIST_CODE_LEN];
    104 /* Distance codes. The first 256 values correspond to the distances
    105  * 3 .. 258, the last 256 values correspond to the top 8 bits of
    106  * the 15 bit distances.
    107  */
    108 
    109 uch _length_code[MAX_MATCH-MIN_MATCH+1];
    110 /* length code for each normalized match length (0 == MIN_MATCH) */
    111 
    112 local int base_length[LENGTH_CODES];
    113 /* First normalized length for each code (0 = MIN_MATCH) */
    114 
    115 local int base_dist[D_CODES];
    116 /* First normalized distance for each code (0 = distance of 1) */
    117 
    118 #else
    119 #  include "trees.h"
    120 #endif /* GEN_TREES_H */
    121 
    122 struct static_tree_desc_s {
    123     const ct_data *static_tree;  /* static tree or NULL */
    124     const intf *extra_bits;      /* extra bits for each code or NULL */
    125     int     extra_base;          /* base index for extra_bits */
    126     int     elems;               /* max number of elements in the tree */
    127     int     max_length;          /* max bit length for the codes */
    128 };
    129 
    130 local static_tree_desc  static_l_desc =
    131 {static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS};
    132 
    133 local static_tree_desc  static_d_desc =
    134 {static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS};
    135 
    136 local static_tree_desc  static_bl_desc =
    137 {(const ct_data *)0, extra_blbits, 0,   BL_CODES, MAX_BL_BITS};
    138 
    139 /* ===========================================================================
    140  * Local (static) routines in this file.
    141  */
    142 
    143 local void tr_static_init OF((void));
    144 local void init_block     OF((deflate_state *s));
    145 local void pqdownheap     OF((deflate_state *s, ct_data *tree, int k));
    146 local void gen_bitlen     OF((deflate_state *s, tree_desc *desc));
    147 local void gen_codes      OF((ct_data *tree, int max_code, ushf *bl_count));
    148 local void build_tree     OF((deflate_state *s, tree_desc *desc));
    149 local void scan_tree      OF((deflate_state *s, ct_data *tree, int max_code));
    150 local void send_tree      OF((deflate_state *s, ct_data *tree, int max_code));
    151 local int  build_bl_tree  OF((deflate_state *s));
    152 local void send_all_trees OF((deflate_state *s, int lcodes, int dcodes,
    153                               int blcodes));
    154 local void compress_block OF((deflate_state *s, ct_data *ltree,
    155                               ct_data *dtree));
    156 local int  detect_data_type OF((deflate_state *s));
    157 local unsigned bi_reverse OF((unsigned value, int length));
    158 local void bi_windup      OF((deflate_state *s));
    159 local void bi_flush       OF((deflate_state *s));
    160 local void copy_block     OF((deflate_state *s, charf *buf, unsigned len,
    161                               int header));
    162 
    163 #ifdef GEN_TREES_H
    164 local void gen_trees_header OF((void));
    165 #endif
    166 
    167 #ifndef DEBUG_ZLIB
    168 #  define send_code(s, c, tree) send_bits(s, tree[c].Code, tree[c].Len)
    169    /* Send a code of the given tree. c and tree must not have side effects */
    170 
    171 #else /* DEBUG_ZLIB */
    172 #  define send_code(s, c, tree) \
    173      { if (z_verbose>2) fprintf(stderr,"\ncd %3d ",(c)); \
    174        send_bits(s, tree[c].Code, tree[c].Len); }
    175 #endif
    176 
    177 /* ===========================================================================
    178  * Output a short LSB first on the stream.
    179  * IN assertion: there is enough room in pendingBuf.
    180  */
    181 #define put_short(s, w) { \
    182     put_byte(s, (uch)((w) & 0xff)); \
    183     put_byte(s, (uch)((ush)(w) >> 8)); \
    184 }
    185 
    186 /* ===========================================================================
    187  * Send a value on a given number of bits.
    188  * IN assertion: length <= 16 and value fits in length bits.
    189  */
    190 #ifdef DEBUG_ZLIB
    191 local void send_bits      OF((deflate_state *s, int value, int length));
    192 
    193 local void send_bits(s, value, length)
    194     deflate_state *s;
    195     int value;  /* value to send */
    196     int length; /* number of bits */
    197 {
    198     Tracevv((stderr," l %2d v %4x ", length, value));
    199     Assert(length > 0 && length <= 15, "invalid length");
    200     s->bits_sent += (ulg)length;
    201 
    202     /* If not enough room in bi_buf, use (valid) bits from bi_buf and
    203      * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
    204      * unused bits in value.
    205      */
    206     if (s->bi_valid > (int)Buf_size - length) {
    207         s->bi_buf |= (ush)value << s->bi_valid;
    208         put_short(s, s->bi_buf);
    209         s->bi_buf = (ush)value >> (Buf_size - s->bi_valid);
    210         s->bi_valid += length - Buf_size;
    211     } else {
    212         s->bi_buf |= (ush)value << s->bi_valid;
    213         s->bi_valid += length;
    214     }
    215 }
    216 #else /* !DEBUG_ZLIB */
    217 
    218 #define send_bits(s, value, length) \
    219 { int len = length;\
    220   if (s->bi_valid > (int)Buf_size - len) {\
    221     int val = value;\
    222     s->bi_buf |= (ush)val << s->bi_valid;\
    223     put_short(s, s->bi_buf);\
    224     s->bi_buf = (ush)val >> (Buf_size - s->bi_valid);\
    225     s->bi_valid += len - Buf_size;\
    226   } else {\
    227     s->bi_buf |= (ush)(value) << s->bi_valid;\
    228     s->bi_valid += len;\
    229   }\
    230 }
    231 #endif /* DEBUG_ZLIB */
    232 
    233 
    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 #ifdef NO_INIT_GLOBAL_POINTERS
    255     static_l_desc.static_tree = static_ltree;
    256     static_l_desc.extra_bits = extra_lbits;
    257     static_d_desc.static_tree = static_dtree;
    258     static_d_desc.extra_bits = extra_dbits;
    259     static_bl_desc.extra_bits = extra_blbits;
    260 #endif
    261 
    262     /* Initialize the mapping length (0..255) -> length code (0..28) */
    263     length = 0;
    264     for (code = 0; code < LENGTH_CODES-1; code++) {
    265         base_length[code] = length;
    266         for (n = 0; n < (1<<extra_lbits[code]); n++) {
    267             _length_code[length++] = (uch)code;
    268         }
    269     }
    270     Assert (length == 256, "tr_static_init: length != 256");
    271     /* Note that the length 255 (match length 258) can be represented
    272      * in two different ways: code 284 + 5 bits or code 285, so we
    273      * overwrite length_code[255] to use the best encoding:
    274      */
    275     _length_code[length-1] = (uch)code;
    276 
    277     /* Initialize the mapping dist (0..32K) -> dist code (0..29) */
    278     dist = 0;
    279     for (code = 0 ; code < 16; code++) {
    280         base_dist[code] = dist;
    281         for (n = 0; n < (1<<extra_dbits[code]); n++) {
    282             _dist_code[dist++] = (uch)code;
    283         }
    284     }
    285     Assert (dist == 256, "tr_static_init: dist != 256");
    286     dist >>= 7; /* from now on, all distances are divided by 128 */
    287     for ( ; code < D_CODES; code++) {
    288         base_dist[code] = dist << 7;
    289         for (n = 0; n < (1<<(extra_dbits[code]-7)); n++) {
    290             _dist_code[256 + dist++] = (uch)code;
    291         }
    292     }
    293     Assert (dist == 256, "tr_static_init: 256+dist != 512");
    294 
    295     /* Construct the codes of the static literal tree */
    296     for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;
    297     n = 0;
    298     while (n <= 143) static_ltree[n++].Len = 8, bl_count[8]++;
    299     while (n <= 255) static_ltree[n++].Len = 9, bl_count[9]++;
    300     while (n <= 279) static_ltree[n++].Len = 7, bl_count[7]++;
    301     while (n <= 287) static_ltree[n++].Len = 8, bl_count[8]++;
    302     /* Codes 286 and 287 do not exist, but we must include them in the
    303      * tree construction to get a canonical Huffman tree (longest code
    304      * all ones)
    305      */
    306     gen_codes((ct_data *)static_ltree, L_CODES+1, bl_count);
    307 
    308     /* The static distance tree is trivial: */
    309     for (n = 0; n < D_CODES; n++) {
    310         static_dtree[n].Len = 5;
    311         static_dtree[n].Code = bi_reverse((unsigned)n, 5);
    312     }
    313     static_init_done = 1;
    314 
    315 #  ifdef GEN_TREES_H
    316     gen_trees_header();
    317 #  endif
    318 #endif /* defined(GEN_TREES_H) || !defined(STDC) */
    319 }
    320 
    321 /* ===========================================================================
    322  * Genererate the file trees.h describing the static trees.
    323  */
    324 #ifdef GEN_TREES_H
    325 #  ifndef DEBUG_ZLIB
    326 #    include <stdio.h>
    327 #  endif
    328 
    329 #  define SEPARATOR(i, last, width) \
    330       ((i) == (last)? "\n};\n\n" :    \
    331        ((i) % (width) == (width)-1 ? ",\n" : ", "))
    332 
    333 void gen_trees_header()
    334 {
    335     FILE *header = fopen("trees.h", "w");
    336     int i;
    337 
    338     Assert (header != NULL, "Can't open trees.h");
    339     fprintf(header,
    340             "/* header created automatically with -DGEN_TREES_H */\n\n");
    341 
    342     fprintf(header, "local const ct_data static_ltree[L_CODES+2] = {\n");
    343     for (i = 0; i < L_CODES+2; i++) {
    344         fprintf(header, "{{%3u},{%3u}}%s", static_ltree[i].Code,
    345                 static_ltree[i].Len, SEPARATOR(i, L_CODES+1, 5));
    346     }
    347 
    348     fprintf(header, "local const ct_data static_dtree[D_CODES] = {\n");
    349     for (i = 0; i < D_CODES; i++) {
    350         fprintf(header, "{{%2u},{%2u}}%s", static_dtree[i].Code,
    351                 static_dtree[i].Len, SEPARATOR(i, D_CODES-1, 5));
    352     }
    353 
    354     fprintf(header, "const uch ZLIB_INTERNAL _dist_code[DIST_CODE_LEN] = {\n");
    355     for (i = 0; i < DIST_CODE_LEN; i++) {
    356         fprintf(header, "%2u%s", _dist_code[i],
    357                 SEPARATOR(i, DIST_CODE_LEN-1, 20));
    358     }
    359 
    360     fprintf(header,
    361         "const uch ZLIB_INTERNAL _length_code[MAX_MATCH-MIN_MATCH+1]= {\n");
    362     for (i = 0; i < MAX_MATCH-MIN_MATCH+1; i++) {
    363         fprintf(header, "%2u%s", _length_code[i],
    364                 SEPARATOR(i, MAX_MATCH-MIN_MATCH, 20));
    365     }
    366 
    367     fprintf(header, "local const int base_length[LENGTH_CODES] = {\n");
    368     for (i = 0; i < LENGTH_CODES; i++) {
    369         fprintf(header, "%1u%s", base_length[i],
    370                 SEPARATOR(i, LENGTH_CODES-1, 20));
    371     }
    372 
    373     fprintf(header, "local const int base_dist[D_CODES] = {\n");
    374     for (i = 0; i < D_CODES; i++) {
    375         fprintf(header, "%5u%s", base_dist[i],
    376                 SEPARATOR(i, D_CODES-1, 10));
    377     }
    378 
    379     fclose(header);
    380 }
    381 #endif /* GEN_TREES_H */
    382 
    383 /* ===========================================================================
    384  * Initialize the tree data structures for a new zlib stream.
    385  */
    386 void ZLIB_INTERNAL _tr_init(s)
    387     deflate_state *s;
    388 {
    389     tr_static_init();
    390 
    391     s->l_desc.dyn_tree = s->dyn_ltree;
    392     s->l_desc.stat_desc = &static_l_desc;
    393 
    394     s->d_desc.dyn_tree = s->dyn_dtree;
    395     s->d_desc.stat_desc = &static_d_desc;
    396 
    397     s->bl_desc.dyn_tree = s->bl_tree;
    398     s->bl_desc.stat_desc = &static_bl_desc;
    399 
    400     s->bi_buf = 0;
    401     s->bi_valid = 0;
    402     s->last_eob_len = 8; /* enough lookahead for inflate */
    403 #ifdef DEBUG_ZLIB
    404     s->compressed_len = 0L;
    405     s->bits_sent = 0L;
    406 #endif
    407 
    408     /* Initialize the first block of the first file: */
    409     init_block(s);
    410 }
    411 
    412 /* ===========================================================================
    413  * Initialize a new block.
    414  */
    415 local void init_block(s)
    416     deflate_state *s;
    417 {
    418     int n; /* iterates over tree elements */
    419 
    420     /* Initialize the trees. */
    421     for (n = 0; n < L_CODES;  n++) s->dyn_ltree[n].Freq = 0;
    422     for (n = 0; n < D_CODES;  n++) s->dyn_dtree[n].Freq = 0;
    423     for (n = 0; n < BL_CODES; n++) s->bl_tree[n].Freq = 0;
    424 
    425     s->dyn_ltree[END_BLOCK].Freq = 1;
    426     s->opt_len = s->static_len = 0L;
    427     s->last_lit = s->matches = 0;
    428 }
    429 
    430 #define SMALLEST 1
    431 /* Index within the heap array of least frequent node in the Huffman tree */
    432 
    433 
    434 /* ===========================================================================
    435  * Remove the smallest element from the heap and recreate the heap with
    436  * one less element. Updates heap and heap_len.
    437  */
    438 #define pqremove(s, tree, top) \
    439 {\
    440     top = s->heap[SMALLEST]; \
    441     s->heap[SMALLEST] = s->heap[s->heap_len--]; \
    442     pqdownheap(s, tree, SMALLEST); \
    443 }
    444 
    445 /* ===========================================================================
    446  * Compares to subtrees, using the tree depth as tie breaker when
    447  * the subtrees have equal frequency. This minimizes the worst case length.
    448  */
    449 #define smaller(tree, n, m, depth) \
    450    (tree[n].Freq < tree[m].Freq || \
    451    (tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))
    452 
    453 /* ===========================================================================
    454  * Restore the heap property by moving down the tree starting at node k,
    455  * exchanging a node with the smallest of its two sons if necessary, stopping
    456  * when the heap property is re-established (each father smaller than its
    457  * two sons).
    458  */
    459 local void pqdownheap(s, tree, k)
    460     deflate_state *s;
    461     ct_data *tree;  /* the tree to restore */
    462     int k;               /* node to move down */
    463 {
    464     int v = s->heap[k];
    465     int j = k << 1;  /* left son of k */
    466     while (j <= s->heap_len) {
    467         /* Set j to the smallest of the two sons: */
    468         if (j < s->heap_len &&
    469             smaller(tree, s->heap[j+1], s->heap[j], s->depth)) {
    470             j++;
    471         }
    472         /* Exit if v is smaller than both sons */
    473         if (smaller(tree, v, s->heap[j], s->depth)) break;
    474 
    475         /* Exchange v with the smallest son */
    476         s->heap[k] = s->heap[j];  k = j;
    477 
    478         /* And continue down the tree, setting j to the left son of k */
    479         j <<= 1;
    480     }
    481     s->heap[k] = v;
    482 }
    483 
    484 /* ===========================================================================
    485  * Compute the optimal bit lengths for a tree and update the total bit length
    486  * for the current block.
    487  * IN assertion: the fields freq and dad are set, heap[heap_max] and
    488  *    above are the tree nodes sorted by increasing frequency.
    489  * OUT assertions: the field len is set to the optimal bit length, the
    490  *     array bl_count contains the frequencies for each bit length.
    491  *     The length opt_len is updated; static_len is also updated if stree is
    492  *     not null.
    493  */
    494 local void gen_bitlen(s, desc)
    495     deflate_state *s;
    496     tree_desc *desc;    /* the tree descriptor */
    497 {
    498     ct_data *tree        = desc->dyn_tree;
    499     int max_code         = desc->max_code;
    500     const ct_data *stree = desc->stat_desc->static_tree;
    501     const intf *extra    = desc->stat_desc->extra_bits;
    502     int base             = desc->stat_desc->extra_base;
    503     int max_length       = desc->stat_desc->max_length;
    504     int h;              /* heap index */
    505     int n, m;           /* iterate over the tree elements */
    506     int bits;           /* bit length */
    507     int xbits;          /* extra bits */
    508     ush f;              /* frequency */
    509     int overflow = 0;   /* number of elements with bit length too large */
    510 
    511     for (bits = 0; bits <= MAX_BITS; bits++) s->bl_count[bits] = 0;
    512 
    513     /* In a first pass, compute the optimal bit lengths (which may
    514      * overflow in the case of the bit length tree).
    515      */
    516     tree[s->heap[s->heap_max]].Len = 0; /* root of the heap */
    517 
    518     for (h = s->heap_max+1; h < HEAP_SIZE; h++) {
    519         n = s->heap[h];
    520         bits = tree[tree[n].Dad].Len + 1;
    521         if (bits > max_length) bits = max_length, overflow++;
    522         tree[n].Len = (ush)bits;
    523         /* We overwrite tree[n].Dad which is no longer needed */
    524 
    525         if (n > max_code) continue; /* not a leaf node */
    526 
    527         s->bl_count[bits]++;
    528         xbits = 0;
    529         if (n >= base) xbits = extra[n-base];
    530         f = tree[n].Freq;
    531         s->opt_len += (ulg)f * (bits + xbits);
    532         if (stree) s->static_len += (ulg)f * (stree[n].Len + xbits);
    533     }
    534     if (overflow == 0) return;
    535 
    536     Trace((stderr,"\nbit length overflow\n"));
    537     /* This happens for example on obj2 and pic of the Calgary corpus */
    538 
    539     /* Find the first bit length which could increase: */
    540     do {
    541         bits = max_length-1;
    542         while (s->bl_count[bits] == 0) bits--;
    543         s->bl_count[bits]--;      /* move one leaf down the tree */
    544         s->bl_count[bits+1] += 2; /* move one overflow item as its brother */
    545         s->bl_count[max_length]--;
    546         /* The brother of the overflow item also moves one step up,
    547          * but this does not affect bl_count[max_length]
    548          */
    549         overflow -= 2;
    550     } while (overflow > 0);
    551 
    552     /* Now recompute all bit lengths, scanning in increasing frequency.
    553      * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
    554      * lengths instead of fixing only the wrong ones. This idea is taken
    555      * from 'ar' written by Haruhiko Okumura.)
    556      */
    557     for (bits = max_length; bits != 0; bits--) {
    558         n = s->bl_count[bits];
    559         while (n != 0) {
    560             m = s->heap[--h];
    561             if (m > max_code) continue;
    562             if ((unsigned) tree[m].Len != (unsigned) bits) {
    563                 Trace((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));
    564                 s->opt_len += ((long)bits - (long)tree[m].Len)
    565                               *(long)tree[m].Freq;
    566                 tree[m].Len = (ush)bits;
    567             }
    568             n--;
    569         }
    570     }
    571 }
    572 
    573 /* ===========================================================================
    574  * Generate the codes for a given tree and bit counts (which need not be
    575  * optimal).
    576  * IN assertion: the array bl_count contains the bit length statistics for
    577  * the given tree and the field len is set for all tree elements.
    578  * OUT assertion: the field code is set for all tree elements of non
    579  *     zero code length.
    580  */
    581 local void gen_codes (tree, max_code, bl_count)
    582     ct_data *tree;             /* the tree to decorate */
    583     int max_code;              /* largest code with non zero frequency */
    584     ushf *bl_count;            /* number of codes at each bit length */
    585 {
    586     ush next_code[MAX_BITS+1]; /* next code value for each bit length */
    587     ush code = 0;              /* running code value */
    588     int bits;                  /* bit index */
    589     int n;                     /* code index */
    590 
    591     /* The distribution counts are first used to generate the code values
    592      * without bit reversal.
    593      */
    594     for (bits = 1; bits <= MAX_BITS; bits++) {
    595         next_code[bits] = code = (code + bl_count[bits-1]) << 1;
    596     }
    597     /* Check that the bit counts in bl_count are consistent. The last code
    598      * must be all ones.
    599      */
    600     Assert (code + bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1,
    601             "inconsistent bit counts");
    602     Tracev((stderr,"\ngen_codes: max_code %d ", max_code));
    603 
    604     for (n = 0;  n <= max_code; n++) {
    605         int len = tree[n].Len;
    606         if (len == 0) continue;
    607         /* Now reverse the bits */
    608         tree[n].Code = bi_reverse(next_code[len]++, len);
    609 
    610         Tracecv(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",
    611              n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len]-1));
    612     }
    613 }
    614 
    615 /* ===========================================================================
    616  * Construct one Huffman tree and assigns the code bit strings and lengths.
    617  * Update the total bit length for the current block.
    618  * IN assertion: the field freq is set for all tree elements.
    619  * OUT assertions: the fields len and code are set to the optimal bit length
    620  *     and corresponding code. The length opt_len is updated; static_len is
    621  *     also updated if stree is not null. The field max_code is set.
    622  */
    623 local void build_tree(s, desc)
    624     deflate_state *s;
    625     tree_desc *desc; /* the tree descriptor */
    626 {
    627     ct_data *tree         = desc->dyn_tree;
    628     const ct_data *stree  = desc->stat_desc->static_tree;
    629     int elems             = desc->stat_desc->elems;
    630     int n, m;          /* iterate over heap elements */
    631     int max_code = -1; /* largest code with non zero frequency */
    632     int node;          /* new node being created */
    633 
    634     /* Construct the initial heap, with least frequent element in
    635      * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
    636      * heap[0] is not used.
    637      */
    638     s->heap_len = 0, s->heap_max = HEAP_SIZE;
    639 
    640     for (n = 0; n < elems; n++) {
    641         if (tree[n].Freq != 0) {
    642             s->heap[++(s->heap_len)] = max_code = n;
    643             s->depth[n] = 0;
    644         } else {
    645             tree[n].Len = 0;
    646         }
    647     }
    648 
    649     /* The pkzip format requires that at least one distance code exists,
    650      * and that at least one bit should be sent even if there is only one
    651      * possible code. So to avoid special checks later on we force at least
    652      * two codes of non zero frequency.
    653      */
    654     while (s->heap_len < 2) {
    655         node = s->heap[++(s->heap_len)] = (max_code < 2 ? ++max_code : 0);
    656         tree[node].Freq = 1;
    657         s->depth[node] = 0;
    658         s->opt_len--; if (stree) s->static_len -= stree[node].Len;
    659         /* node is 0 or 1 so it does not have extra bits */
    660     }
    661     desc->max_code = max_code;
    662 
    663     /* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
    664      * establish sub-heaps of increasing lengths:
    665      */
    666     for (n = s->heap_len/2; n >= 1; n--) pqdownheap(s, tree, n);
    667 
    668     /* Construct the Huffman tree by repeatedly combining the least two
    669      * frequent nodes.
    670      */
    671     node = elems;              /* next internal node of the tree */
    672     do {
    673         pqremove(s, tree, n);  /* n = node of least frequency */
    674         m = s->heap[SMALLEST]; /* m = node of next least frequency */
    675 
    676         s->heap[--(s->heap_max)] = n; /* keep the nodes sorted by frequency */
    677         s->heap[--(s->heap_max)] = m;
    678 
    679         /* Create a new node father of n and m */
    680         tree[node].Freq = tree[n].Freq + tree[m].Freq;
    681         s->depth[node] = (uch)((s->depth[n] >= s->depth[m] ?
    682                                 s->depth[n] : s->depth[m]) + 1);
    683         tree[n].Dad = tree[m].Dad = (ush)node;
    684 #ifdef DUMP_BL_TREE
    685         if (tree == s->bl_tree) {
    686             fprintf(stderr,"\nnode %d(%d), sons %d(%d) %d(%d)",
    687                     node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq);
    688         }
    689 #endif
    690         /* and insert the new node in the heap */
    691         s->heap[SMALLEST] = node++;
    692         pqdownheap(s, tree, SMALLEST);
    693 
    694     } while (s->heap_len >= 2);
    695 
    696     s->heap[--(s->heap_max)] = s->heap[SMALLEST];
    697 
    698     /* At this point, the fields freq and dad are set. We can now
    699      * generate the bit lengths.
    700      */
    701     gen_bitlen(s, (tree_desc *)desc);
    702 
    703     /* The field len is now set, we can generate the bit codes */
    704     gen_codes ((ct_data *)tree, max_code, s->bl_count);
    705 }
    706 
    707 /* ===========================================================================
    708  * Scan a literal or distance tree to determine the frequencies of the codes
    709  * in the bit length tree.
    710  */
    711 local void scan_tree (s, tree, max_code)
    712     deflate_state *s;
    713     ct_data *tree;   /* the tree to be scanned */
    714     int max_code;    /* and its largest code of non zero frequency */
    715 {
    716     int n;                     /* iterates over all tree elements */
    717     int prevlen = -1;          /* last emitted length */
    718     int curlen;                /* length of current code */
    719     int nextlen = tree[0].Len; /* length of next code */
    720     int count = 0;             /* repeat count of the current code */
    721     int max_count = 7;         /* max repeat count */
    722     int min_count = 4;         /* min repeat count */
    723 
    724     if (nextlen == 0) max_count = 138, min_count = 3;
    725     tree[max_code+1].Len = (ush)0xffff; /* guard */
    726 
    727     for (n = 0; n <= max_code; n++) {
    728         curlen = nextlen; nextlen = tree[n+1].Len;
    729         if (++count < max_count && curlen == nextlen) {
    730             continue;
    731         } else if (count < min_count) {
    732             s->bl_tree[curlen].Freq += count;
    733         } else if (curlen != 0) {
    734             if (curlen != prevlen) s->bl_tree[curlen].Freq++;
    735             s->bl_tree[REP_3_6].Freq++;
    736         } else if (count <= 10) {
    737             s->bl_tree[REPZ_3_10].Freq++;
    738         } else {
    739             s->bl_tree[REPZ_11_138].Freq++;
    740         }
    741         count = 0; prevlen = curlen;
    742         if (nextlen == 0) {
    743             max_count = 138, min_count = 3;
    744         } else if (curlen == nextlen) {
    745             max_count = 6, min_count = 3;
    746         } else {
    747             max_count = 7, min_count = 4;
    748         }
    749     }
    750 }
    751 
    752 /* ===========================================================================
    753  * Send a literal or distance tree in compressed form, using the codes in
    754  * bl_tree.
    755  */
    756 local void send_tree (s, tree, max_code)
    757     deflate_state *s;
    758     ct_data *tree; /* the tree to be scanned */
    759     int max_code;       /* and its largest code of non zero frequency */
    760 {
    761     int n;                     /* iterates over all tree elements */
    762     int prevlen = -1;          /* last emitted length */
    763     int curlen;                /* length of current code */
    764     int nextlen = tree[0].Len; /* length of next code */
    765     int count = 0;             /* repeat count of the current code */
    766     int max_count = 7;         /* max repeat count */
    767     int min_count = 4;         /* min repeat count */
    768 
    769     /* tree[max_code+1].Len = -1; */  /* guard already set */
    770     if (nextlen == 0) max_count = 138, min_count = 3;
    771 
    772     for (n = 0; n <= max_code; n++) {
    773         curlen = nextlen; nextlen = tree[n+1].Len;
    774         if (++count < max_count && curlen == nextlen) {
    775             continue;
    776         } else if (count < min_count) {
    777             do { send_code(s, curlen, s->bl_tree); } while (--count != 0);
    778 
    779         } else if (curlen != 0) {
    780             if (curlen != prevlen) {
    781                 send_code(s, curlen, s->bl_tree); count--;
    782             }
    783             Assert(count >= 3 && count <= 6, " 3_6?");
    784             send_code(s, REP_3_6, s->bl_tree); send_bits(s, count-3, 2);
    785 
    786         } else if (count <= 10) {
    787             send_code(s, REPZ_3_10, s->bl_tree); send_bits(s, count-3, 3);
    788 
    789         } else {
    790             send_code(s, REPZ_11_138, s->bl_tree); send_bits(s, count-11, 7);
    791         }
    792         count = 0; prevlen = curlen;
    793         if (nextlen == 0) {
    794             max_count = 138, min_count = 3;
    795         } else if (curlen == nextlen) {
    796             max_count = 6, min_count = 3;
    797         } else {
    798             max_count = 7, min_count = 4;
    799         }
    800     }
    801 }
    802 
    803 /* ===========================================================================
    804  * Construct the Huffman tree for the bit lengths and return the index in
    805  * bl_order of the last bit length code to send.
    806  */
    807 local int build_bl_tree(s)
    808     deflate_state *s;
    809 {
    810     int max_blindex;  /* index of last bit length code of non zero freq */
    811 
    812     /* Determine the bit length frequencies for literal and distance trees */
    813     scan_tree(s, (ct_data *)s->dyn_ltree, s->l_desc.max_code);
    814     scan_tree(s, (ct_data *)s->dyn_dtree, s->d_desc.max_code);
    815 
    816     /* Build the bit length tree: */
    817     build_tree(s, (tree_desc *)(&(s->bl_desc)));
    818     /* opt_len now includes the length of the tree representations, except
    819      * the lengths of the bit lengths codes and the 5+5+4 bits for the counts.
    820      */
    821 
    822     /* Determine the number of bit length codes to send. The pkzip format
    823      * requires that at least 4 bit length codes be sent. (appnote.txt says
    824      * 3 but the actual value used is 4.)
    825      */
    826     for (max_blindex = BL_CODES-1; max_blindex >= 3; max_blindex--) {
    827         if (s->bl_tree[bl_order[max_blindex]].Len != 0) break;
    828     }
    829     /* Update opt_len to include the bit length tree and counts */
    830     s->opt_len += 3*(max_blindex+1) + 5+5+4;
    831     Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld",
    832             s->opt_len, s->static_len));
    833 
    834     return max_blindex;
    835 }
    836 
    837 /* ===========================================================================
    838  * Send the header for a block using dynamic Huffman trees: the counts, the
    839  * lengths of the bit length codes, the literal tree and the distance tree.
    840  * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
    841  */
    842 local void send_all_trees(s, lcodes, dcodes, blcodes)
    843     deflate_state *s;
    844     int lcodes, dcodes, blcodes; /* number of codes for each tree */
    845 {
    846     int rank;                    /* index in bl_order */
    847 
    848     Assert (lcodes >= 257 && dcodes >= 1 && blcodes >= 4, "not enough codes");
    849     Assert (lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
    850             "too many codes");
    851     Tracev((stderr, "\nbl counts: "));
    852     send_bits(s, lcodes-257, 5); /* not +255 as stated in appnote.txt */
    853     send_bits(s, dcodes-1,   5);
    854     send_bits(s, blcodes-4,  4); /* not -3 as stated in appnote.txt */
    855     for (rank = 0; rank < blcodes; rank++) {
    856         Tracev((stderr, "\nbl code %2d ", bl_order[rank]));
    857         send_bits(s, s->bl_tree[bl_order[rank]].Len, 3);
    858     }
    859     Tracev((stderr, "\nbl tree: sent %ld", s->bits_sent));
    860 
    861     send_tree(s, (ct_data *)s->dyn_ltree, lcodes-1); /* literal tree */
    862     Tracev((stderr, "\nlit tree: sent %ld", s->bits_sent));
    863 
    864     send_tree(s, (ct_data *)s->dyn_dtree, dcodes-1); /* distance tree */
    865     Tracev((stderr, "\ndist tree: sent %ld", s->bits_sent));
    866 }
    867 
    868 /* ===========================================================================
    869  * Send a stored block
    870  */
    871 void ZLIB_INTERNAL _tr_stored_block(s, buf, stored_len, last)
    872     deflate_state *s;
    873     charf *buf;       /* input block */
    874     ulg stored_len;   /* length of input block */
    875     int last;         /* one if this is the last block for a file */
    876 {
    877     send_bits(s, (STORED_BLOCK<<1)+last, 3);    /* send block type */
    878 #ifdef DEBUG_ZLIB
    879     s->compressed_len = (s->compressed_len + 3 + 7) & (ulg)~7L;
    880     s->compressed_len += (stored_len + 4) << 3;
    881 #endif
    882     copy_block(s, buf, (unsigned)stored_len, 1); /* with header */
    883 }
    884 
    885 /* ===========================================================================
    886  * Send one empty static block to give enough lookahead for inflate.
    887  * This takes 10 bits, of which 7 may remain in the bit buffer.
    888  * The current inflate code requires 9 bits of lookahead. If the
    889  * last two codes for the previous block (real code plus EOB) were coded
    890  * on 5 bits or less, inflate may have only 5+3 bits of lookahead to decode
    891  * the last real code. In this case we send two empty static blocks instead
    892  * of one. (There are no problems if the previous block is stored or fixed.)
    893  * To simplify the code, we assume the worst case of last real code encoded
    894  * on one bit only.
    895  */
    896 void ZLIB_INTERNAL _tr_align(s)
    897     deflate_state *s;
    898 {
    899     send_bits(s, STATIC_TREES<<1, 3);
    900     send_code(s, END_BLOCK, static_ltree);
    901 #ifdef DEBUG_ZLIB
    902     s->compressed_len += 10L; /* 3 for block type, 7 for EOB */
    903 #endif
    904     bi_flush(s);
    905     /* Of the 10 bits for the empty block, we have already sent
    906      * (10 - bi_valid) bits. The lookahead for the last real code (before
    907      * the EOB of the previous block) was thus at least one plus the length
    908      * of the EOB plus what we have just sent of the empty static block.
    909      */
    910     if (1 + s->last_eob_len + 10 - s->bi_valid < 9) {
    911         send_bits(s, STATIC_TREES<<1, 3);
    912         send_code(s, END_BLOCK, static_ltree);
    913 #ifdef DEBUG_ZLIB
    914         s->compressed_len += 10L;
    915 #endif
    916         bi_flush(s);
    917     }
    918     s->last_eob_len = 7;
    919 }
    920 
    921 /* ===========================================================================
    922  * Determine the best encoding for the current block: dynamic trees, static
    923  * trees or store, and output the encoded block to the zip file.
    924  */
    925 void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last)
    926     deflate_state *s;
    927     charf *buf;       /* input block, or NULL if too old */
    928     ulg stored_len;   /* length of input block */
    929     int last;         /* one if this is the last block for a file */
    930 {
    931     ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
    932     int max_blindex = 0;  /* index of last bit length code of non zero freq */
    933 
    934     /* Build the Huffman trees unless a stored block is forced */
    935     if (s->level > 0) {
    936 
    937         /* Check if the file is binary or text */
    938         if (s->strm->data_type == Z_UNKNOWN)
    939             s->strm->data_type = detect_data_type(s);
    940 
    941         /* Construct the literal and distance trees */
    942         build_tree(s, (tree_desc *)(&(s->l_desc)));
    943         Tracev((stderr, "\nlit data: dyn %ld, stat %ld", s->opt_len,
    944                 s->static_len));
    945 
    946         build_tree(s, (tree_desc *)(&(s->d_desc)));
    947         Tracev((stderr, "\ndist data: dyn %ld, stat %ld", s->opt_len,
    948                 s->static_len));
    949         /* At this point, opt_len and static_len are the total bit lengths of
    950          * the compressed block data, excluding the tree representations.
    951          */
    952 
    953         /* Build the bit length tree for the above two trees, and get the index
    954          * in bl_order of the last bit length code to send.
    955          */
    956         max_blindex = build_bl_tree(s);
    957 
    958         /* Determine the best encoding. Compute the block lengths in bytes. */
    959         opt_lenb = (s->opt_len+3+7)>>3;
    960         static_lenb = (s->static_len+3+7)>>3;
    961 
    962         Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ",
    963                 opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len,
    964                 s->last_lit));
    965 
    966         if (static_lenb <= opt_lenb) opt_lenb = static_lenb;
    967 
    968     } else {
    969         Assert(buf != (char*)0, "lost buf");
    970         opt_lenb = static_lenb = stored_len + 5; /* force a stored block */
    971     }
    972 
    973 #ifdef FORCE_STORED
    974     if (buf != (char*)0) { /* force stored block */
    975 #else
    976     if (stored_len+4 <= opt_lenb && buf != (char*)0) {
    977                        /* 4: two words for the lengths */
    978 #endif
    979         /* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
    980          * Otherwise we can't have processed more than WSIZE input bytes since
    981          * the last block flush, because compression would have been
    982          * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
    983          * transform a block into a stored block.
    984          */
    985         _tr_stored_block(s, buf, stored_len, last);
    986 
    987 #ifdef FORCE_STATIC
    988     } else if (static_lenb >= 0) { /* force static trees */
    989 #else
    990     } else if (s->strategy == Z_FIXED || static_lenb == opt_lenb) {
    991 #endif
    992         send_bits(s, (STATIC_TREES<<1)+last, 3);
    993         compress_block(s, (ct_data *)static_ltree, (ct_data *)static_dtree);
    994 #ifdef DEBUG_ZLIB
    995         s->compressed_len += 3 + s->static_len;
    996 #endif
    997     } else {
    998         send_bits(s, (DYN_TREES<<1)+last, 3);
    999         send_all_trees(s, s->l_desc.max_code+1, s->d_desc.max_code+1,
   1000                        max_blindex+1);
   1001         compress_block(s, (ct_data *)s->dyn_ltree, (ct_data *)s->dyn_dtree);
   1002 #ifdef DEBUG_ZLIB
   1003         s->compressed_len += 3 + s->opt_len;
   1004 #endif
   1005     }
   1006     Assert (s->compressed_len == s->bits_sent, "bad compressed size");
   1007     /* The above check is made mod 2^32, for files larger than 512 MB
   1008      * and uLong implemented on 32 bits.
   1009      */
   1010     init_block(s);
   1011 
   1012     if (last) {
   1013         bi_windup(s);
   1014 #ifdef DEBUG_ZLIB
   1015         s->compressed_len += 7;  /* align on byte boundary */
   1016 #endif
   1017     }
   1018     Tracev((stderr,"\ncomprlen %lu(%lu) ", s->compressed_len>>3,
   1019            s->compressed_len-7*last));
   1020 }
   1021 
   1022 /* ===========================================================================
   1023  * Save the match info and tally the frequency counts. Return true if
   1024  * the current block must be flushed.
   1025  */
   1026 int ZLIB_INTERNAL _tr_tally (s, dist, lc)
   1027     deflate_state *s;
   1028     unsigned dist;  /* distance of matched string */
   1029     unsigned lc;    /* match length-MIN_MATCH or unmatched char (if dist==0) */
   1030 {
   1031     s->d_buf[s->last_lit] = (ush)dist;
   1032     s->l_buf[s->last_lit++] = (uch)lc;
   1033     if (dist == 0) {
   1034         /* lc is the unmatched char */
   1035         s->dyn_ltree[lc].Freq++;
   1036     } else {
   1037         s->matches++;
   1038         /* Here, lc is the match length - MIN_MATCH */
   1039         dist--;             /* dist = match distance - 1 */
   1040         Assert((ush)dist < (ush)MAX_DIST(s) &&
   1041                (ush)lc <= (ush)(MAX_MATCH-MIN_MATCH) &&
   1042                (ush)d_code(dist) < (ush)D_CODES,  "_tr_tally: bad match");
   1043 
   1044         s->dyn_ltree[_length_code[lc]+LITERALS+1].Freq++;
   1045         s->dyn_dtree[d_code(dist)].Freq++;
   1046     }
   1047 
   1048 #ifdef TRUNCATE_BLOCK
   1049     /* Try to guess if it is profitable to stop the current block here */
   1050     if ((s->last_lit & 0x1fff) == 0 && s->level > 2) {
   1051         /* Compute an upper bound for the compressed length */
   1052         ulg out_length = (ulg)s->last_lit*8L;
   1053         ulg in_length = (ulg)((long)s->strstart - s->block_start);
   1054         int dcode;
   1055         for (dcode = 0; dcode < D_CODES; dcode++) {
   1056             out_length += (ulg)s->dyn_dtree[dcode].Freq *
   1057                 (5L+extra_dbits[dcode]);
   1058         }
   1059         out_length >>= 3;
   1060         Tracev((stderr,"\nlast_lit %u, in %ld, out ~%ld(%ld%%) ",
   1061                s->last_lit, in_length, out_length,
   1062                100L - out_length*100L/in_length));
   1063         if (s->matches < s->last_lit/2 && out_length < in_length/2) return 1;
   1064     }
   1065 #endif
   1066     return (s->last_lit == s->lit_bufsize-1);
   1067     /* We avoid equality with lit_bufsize because of wraparound at 64K
   1068      * on 16 bit machines and because stored blocks are restricted to
   1069      * 64K-1 bytes.
   1070      */
   1071 }
   1072 
   1073 /* ===========================================================================
   1074  * Send the block data compressed using the given Huffman trees
   1075  */
   1076 local void compress_block(s, ltree, dtree)
   1077     deflate_state *s;
   1078     ct_data *ltree; /* literal tree */
   1079     ct_data *dtree; /* distance tree */
   1080 {
   1081     unsigned dist;      /* distance of matched string */
   1082     int lc;             /* match length or unmatched char (if dist == 0) */
   1083     unsigned lx = 0;    /* running index in l_buf */
   1084     unsigned code;      /* the code to send */
   1085     int extra;          /* number of extra bits to send */
   1086 
   1087     if (s->last_lit != 0) do {
   1088         dist = s->d_buf[lx];
   1089         lc = s->l_buf[lx++];
   1090         if (dist == 0) {
   1091             send_code(s, lc, ltree); /* send a literal byte */
   1092             Tracecv(isgraph(lc), (stderr," '%c' ", lc));
   1093         } else {
   1094             /* Here, lc is the match length - MIN_MATCH */
   1095             code = _length_code[lc];
   1096             send_code(s, code+LITERALS+1, ltree); /* send the length code */
   1097             extra = extra_lbits[code];
   1098             if (extra != 0) {
   1099                 lc -= base_length[code];
   1100                 send_bits(s, lc, extra);       /* send the extra length bits */
   1101             }
   1102             dist--; /* dist is now the match distance - 1 */
   1103             code = d_code(dist);
   1104             Assert (code < D_CODES, "bad d_code");
   1105 
   1106             send_code(s, code, dtree);       /* send the distance code */
   1107             extra = extra_dbits[code];
   1108             if (extra != 0) {
   1109                 dist -= base_dist[code];
   1110                 send_bits(s, dist, extra);   /* send the extra distance bits */
   1111             }
   1112         } /* literal or match pair ? */
   1113 
   1114         /* Check that the overlay between pending_buf and d_buf+l_buf is ok: */
   1115         Assert((uInt)(s->pending) < s->lit_bufsize + 2*lx,
   1116                "pendingBuf overflow");
   1117 
   1118     } while (lx < s->last_lit);
   1119 
   1120     send_code(s, END_BLOCK, ltree);
   1121     s->last_eob_len = ltree[END_BLOCK].Len;
   1122 }
   1123 
   1124 /* ===========================================================================
   1125  * Check if the data type is TEXT or BINARY, using the following algorithm:
   1126  * - TEXT if the two conditions below are satisfied:
   1127  *    a) There are no non-portable control characters belonging to the
   1128  *       "black list" (0..6, 14..25, 28..31).
   1129  *    b) There is at least one printable character belonging to the
   1130  *       "white list" (9 {TAB}, 10 {LF}, 13 {CR}, 32..255).
   1131  * - BINARY otherwise.
   1132  * - The following partially-portable control characters form a
   1133  *   "gray list" that is ignored in this detection algorithm:
   1134  *   (7 {BEL}, 8 {BS}, 11 {VT}, 12 {FF}, 26 {SUB}, 27 {ESC}).
   1135  * IN assertion: the fields Freq of dyn_ltree are set.
   1136  */
   1137 local int detect_data_type(s)
   1138     deflate_state *s;
   1139 {
   1140     /* black_mask is the bit mask of black-listed bytes
   1141      * set bits 0..6, 14..25, and 28..31
   1142      * 0xf3ffc07f = binary 11110011111111111100000001111111
   1143      */
   1144     unsigned long black_mask = 0xf3ffc07fUL;
   1145     int n;
   1146 
   1147     /* Check for non-textual ("black-listed") bytes. */
   1148     for (n = 0; n <= 31; n++, black_mask >>= 1)
   1149         if ((black_mask & 1) && (s->dyn_ltree[n].Freq != 0))
   1150             return Z_BINARY;
   1151 
   1152     /* Check for textual ("white-listed") bytes. */
   1153     if (s->dyn_ltree[9].Freq != 0 || s->dyn_ltree[10].Freq != 0
   1154             || s->dyn_ltree[13].Freq != 0)
   1155         return Z_TEXT;
   1156     for (n = 32; n < LITERALS; n++)
   1157         if (s->dyn_ltree[n].Freq != 0)
   1158             return Z_TEXT;
   1159 
   1160     /* There are no "black-listed" or "white-listed" bytes:
   1161      * this stream either is empty or has tolerated ("gray-listed") bytes only.
   1162      */
   1163     return Z_BINARY;
   1164 }
   1165 
   1166 /* ===========================================================================
   1167  * Reverse the first len bits of a code, using straightforward code (a faster
   1168  * method would use a table)
   1169  * IN assertion: 1 <= len <= 15
   1170  */
   1171 local unsigned bi_reverse(code, len)
   1172     unsigned code; /* the value to invert */
   1173     int len;       /* its bit length */
   1174 {
   1175     register unsigned res = 0;
   1176     do {
   1177         res |= code & 1;
   1178         code >>= 1, res <<= 1;
   1179     } while (--len > 0);
   1180     return res >> 1;
   1181 }
   1182 
   1183 /* ===========================================================================
   1184  * Flush the bit buffer, keeping at most 7 bits in it.
   1185  */
   1186 local void bi_flush(s)
   1187     deflate_state *s;
   1188 {
   1189     if (s->bi_valid == 16) {
   1190         put_short(s, s->bi_buf);
   1191         s->bi_buf = 0;
   1192         s->bi_valid = 0;
   1193     } else if (s->bi_valid >= 8) {
   1194         put_byte(s, (Byte)s->bi_buf);
   1195         s->bi_buf >>= 8;
   1196         s->bi_valid -= 8;
   1197     }
   1198 }
   1199 
   1200 /* ===========================================================================
   1201  * Flush the bit buffer and align the output on a byte boundary
   1202  */
   1203 local void bi_windup(s)
   1204     deflate_state *s;
   1205 {
   1206     if (s->bi_valid > 8) {
   1207         put_short(s, s->bi_buf);
   1208     } else if (s->bi_valid > 0) {
   1209         put_byte(s, (Byte)s->bi_buf);
   1210     }
   1211     s->bi_buf = 0;
   1212     s->bi_valid = 0;
   1213 #ifdef DEBUG_ZLIB
   1214     s->bits_sent = (s->bits_sent+7) & ~7;
   1215 #endif
   1216 }
   1217 
   1218 /* ===========================================================================
   1219  * Copy a stored block, storing first the length and its
   1220  * one's complement if requested.
   1221  */
   1222 local void copy_block(s, buf, len, header)
   1223     deflate_state *s;
   1224     charf    *buf;    /* the input data */
   1225     unsigned len;     /* its length */
   1226     int      header;  /* true if block header must be written */
   1227 {
   1228     bi_windup(s);        /* align on byte boundary */
   1229     s->last_eob_len = 8; /* enough lookahead for inflate */
   1230 
   1231     if (header) {
   1232         put_short(s, (ush)len);
   1233         put_short(s, (ush)~len);
   1234 #ifdef DEBUG_ZLIB
   1235         s->bits_sent += 2*16;
   1236 #endif
   1237     }
   1238 #ifdef DEBUG_ZLIB
   1239     s->bits_sent += (ulg)len<<3;
   1240 #endif
   1241     while (len--) {
   1242         put_byte(s, *buf++);
   1243     }
   1244 }
   1245