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

  * Copyright (C) 1995-2005 Jean-loup Gailly

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

  */

 /*

  *  ALGORITHM

  *

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

  *      common source values are represented by shorter bit sequences.

  *

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

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

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

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

  * in the deflate specification.

  *

  *  REFERENCES

  *

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

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

  *

  *      Storer, James A.

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

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

  *

  *      Sedgewick, R.

  *          Algorithms, p290.

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

  */

 /* @(#) $Id$ */

 /* #define GEN_TREES_H */

 #include "deflate.h"

 #ifdef DEBUG

 #  include <ctype.h>

 #endif

 /* ===========================================================================

  * Constants

  */

 #define MAX_BL_BITS 7

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

 #define END_BLOCK 256

 /* end of block literal code */

 #define REP_3_6      16

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

 #define REPZ_3_10    17

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

 #define REPZ_11_138  18

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

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

    = {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};

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

    = {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};

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

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

 local const uch bl_order[BL_CODES]

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

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

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

  */

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

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

  * more than 16 bits on some systems.)

  */

 /* ===========================================================================

  * Local data. These are initialized only once.

  */

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

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

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

 local ct_data static_ltree[L_CODES+2];

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

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

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

  * below).

  */

 local ct_data static_dtree[D_CODES];

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

  * 5 bits.)

  */

 uch _dist_code[DIST_CODE_LEN];

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

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

  * the 15 bit distances.

  */

 uch _length_code[MAX_MATCH-MIN_MATCH+1];

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

 local int base_length[LENGTH_CODES];

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

 local int base_dist[D_CODES];

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

 #else

 #  include "trees.h"

 #endif /* GEN_TREES_H */

 struct static_tree_desc_s {

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

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

     int     extra_base;          /* base index for extra_bits */

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

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

 };

 local static_tree_desc  static_l_desc =

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

 local static_tree_desc  static_d_desc =

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

 local static_tree_desc  static_bl_desc =

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

 /* ===========================================================================

  * Local (static) routines in this file.

  */

 local void tr_static_init OF((void));

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

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

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

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

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

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

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

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

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

                               int blcodes));

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

                               ct_data *dtree));

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

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

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

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

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

                               int header));

 #ifdef GEN_TREES_H

 local void gen_trees_header OF((void));

 #endif

 #ifndef DEBUG

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

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

 #else /* DEBUG */

 #  define send_code(s, c, tree) \

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

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

 #endif

 /* ===========================================================================

  * Output a short LSB first on the stream.

  * IN assertion: there is enough room in pendingBuf.

  */

 #define put_short(s, w) { \

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

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

 }

 /* ===========================================================================

  * Send a value on a given number of bits.

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

  */

 #ifdef DEBUG

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

 local void send_bits(s, value, length)

     deflate_state *s;

     int value;  /* value to send */

     int length; /* number of bits */

 {

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

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

     s->bits_sent += (ulg)length;

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

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

      * unused bits in value.

      */

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

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

         put_short(s, s->bi_buf);

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

         s->bi_valid += length - Buf_size;

     } else {

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

         s->bi_valid += length;

     }

 }

 #else /* !DEBUG */

 #define send_bits(s, value, length) \

 { int len = length;\

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

     int val = value;\

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

     put_short(s, s->bi_buf);\

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

     s->bi_valid += len - Buf_size;\

   } else {\

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

     s->bi_valid += len;\

   }\

 }

 #endif /* DEBUG */

 /* the arguments must not have side effects */

 /* ===========================================================================

  * Initialize the various 'constant' tables.

  */

 local void tr_static_init()

 {

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

     static int static_init_done = 0;

     int n;        /* iterates over tree elements */

     int bits;     /* bit counter */

     int length;   /* length value */

     int code;     /* code value */

     int dist;     /* distance index */

     ush bl_count[MAX_BITS+1];

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

     if (static_init_done) return;

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

     static_l_desc.static_tree = static_ltree;

     static_l_desc.extra_bits = extra_lbits;

     static_d_desc.static_tree = static_dtree;

     static_d_desc.extra_bits = extra_dbits;

     static_bl_desc.extra_bits = extra_blbits;

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

     length = 0;

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

         base_length[code] = length;

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

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

         }

     }

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

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

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

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

      */

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

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

     dist = 0;

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

         base_dist[code] = dist;

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

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

         }

     }

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

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

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

         base_dist[code] = dist << 7;

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

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

         }

     }

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

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

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

     n = 0;

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

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

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

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

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

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

      * all ones)

      */

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

     /* The static distance tree is trivial: */

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

         static_dtree[n].Len = 5;

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

     }

     static_init_done = 1;

 #  ifdef GEN_TREES_H

     gen_trees_header();

 #  endif

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

 }

 /* ===========================================================================

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

  */

 #ifdef GEN_TREES_H

 #  ifndef DEBUG

 #    include <stdio.h>

 #  endif

 #  define SEPARATOR(i, last, width) \

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

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

 void gen_trees_header()

 {

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

     int i;

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

     fprintf(header,

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

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

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

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

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

     }

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

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

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

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

     }

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

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

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

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

     }

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

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

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

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

     }

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

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

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

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

     }

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

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

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

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

     }

     fclose(header);

 }

 #endif /* GEN_TREES_H */

 /* ===========================================================================

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

  */

 void _tr_init(s)

     deflate_state *s;

 {

     tr_static_init();

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

     s->l_desc.stat_desc = &static_l_desc;

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

     s->d_desc.stat_desc = &static_d_desc;

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

     s->bl_desc.stat_desc = &static_bl_desc;

     s->bi_buf = 0;

     s->bi_valid = 0;

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

 #ifdef DEBUG

     s->compressed_len = 0L;

     s->bits_sent = 0L;

 #endif

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

     init_block(s);

 }

 /* ===========================================================================

  * Initialize a new block.

  */

 local void init_block(s)

     deflate_state *s;

 {

     int n; /* iterates over tree elements */

     /* Initialize the trees. */

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

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

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

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

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

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

 }

 #define SMALLEST 1

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

 /* ===========================================================================

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

  * one less element. Updates heap and heap_len.

  */

 #define pqremove(s, tree, top) \

 {\

     top = s->heap[SMALLEST]; \

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

     pqdownheap(s, tree, SMALLEST); \

 }

 /* ===========================================================================

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

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

  */

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

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

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

 /* ===========================================================================

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

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

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

  * two sons).

  */

 local void pqdownheap(s, tree, k)

     deflate_state *s;

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

     int k;               /* node to move down */

 {

     int v = s->heap[k];

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

     while (j <= s->heap_len) {

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

         if (j < s->heap_len &&

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

             j++;

         }

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

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

         /* Exchange v with the smallest son */

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

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

         j <<= 1;

     }

     s->heap[k] = v;

 }

 /* ===========================================================================

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

  * for the current block.

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

  *    above are the tree nodes sorted by increasing frequency.

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

  *     array bl_count contains the frequencies for each bit length.

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

  *     not null.

  */

 local void gen_bitlen(s, desc)

     deflate_state *s;

     tree_desc *desc;    /* the tree descriptor */

 {

     ct_data *tree        = desc->dyn_tree;

     int max_code         = desc->max_code;

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

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

     int base             = desc->stat_desc->extra_base;

     int max_length       = desc->stat_desc->max_length;

     int h;              /* heap index */

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

     int bits;           /* bit length */

     int xbits;          /* extra bits */

     ush f;              /* frequency */

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

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

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

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

      */

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

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

         n = s->heap[h];

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

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

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

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

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

         s->bl_count[bits]++;

         xbits = 0;

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

         f = tree[n].Freq;

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

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

     }

     if (overflow == 0) return;

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

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

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

     do {

         bits = max_length-1;

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

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

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

         s->bl_count[max_length]--;

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

          * but this does not affect bl_count[max_length]

          */

         overflow -= 2;

     } while (overflow > 0);

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

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

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

      * from 'ar' written by Haruhiko Okumura.)

      */

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

         n = s->bl_count[bits];

         while (n != 0) {

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

             if (m > max_code) continue;

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

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

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

                               *(long)tree[m].Freq;

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

             }

             n--;

         }

     }

 }

 /* ===========================================================================

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

  * optimal).

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

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

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

  *     zero code length.

  */

 local void gen_codes (tree, max_code, bl_count)

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

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

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

 {

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

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

     int bits;                  /* bit index */

     int n;                     /* code index */

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

      * without bit reversal.

      */

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

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

     }

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

      * must be all ones.

      */

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

             "inconsistent bit counts");

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

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

         int len = tree[n].Len;

         if (len == 0) continue;

         /* Now reverse the bits */

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

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

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

     }

 }

 /* ===========================================================================

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

  * Update the total bit length for the current block.

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

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

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

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

  */

 local void build_tree(s, desc)

     deflate_state *s;

     tree_desc *desc; /* the tree descriptor */

 {

     ct_data *tree         = desc->dyn_tree;

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

     int elems             = desc->stat_desc->elems;

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

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

     int node;          /* new node being created */

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

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

      * heap[0] is not used.

      */

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

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

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

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

             s->depth[n] = 0;

         } else {

             tree[n].Len = 0;

         }

     }

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

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

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

      * two codes of non zero frequency.

      */

     while (s->heap_len < 2) {

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

         tree[node].Freq = 1;

         s->depth[node] = 0;

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

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

     }

     desc->max_code = max_code;

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

      * establish sub-heaps of increasing lengths:

      */

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

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

      * frequent nodes.

      */

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

     do {

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

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

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

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

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

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

         s->depth[node] = (uch)((s->depth[n] >= s->depth[m] ?

                                 s->depth[n] : s->depth[m]) + 1);

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

 #ifdef DUMP_BL_TREE

         if (tree == s->bl_tree) {

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

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

         }

 #endif

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

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

         pqdownheap(s, tree, SMALLEST);

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

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

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

      * generate the bit lengths.

      */

     gen_bitlen(s, (tree_desc *)desc);

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

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

 }

 /* ===========================================================================

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

  * in the bit length tree.

  */

 local void scan_tree (s, tree, max_code)

     deflate_state *s;

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

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

 {

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

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

     int curlen;                /* length of current code */

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

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

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

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

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

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

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

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

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

             continue;

         } else if (count < min_count) {

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

         } else if (curlen != 0) {

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

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

         } else if (count <= 10) {

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

         } else {

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

         }

         count = 0; prevlen = curlen;

         if (nextlen == 0) {

             max_count = 138, min_count = 3;

         } else if (curlen == nextlen) {

             max_count = 6, min_count = 3;

         } else {

             max_count = 7, min_count = 4;

         }

     }

 }

 /* ===========================================================================

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

  * bl_tree.

  */

 local void send_tree (s, tree, max_code)

     deflate_state *s;

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

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

 {

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

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

     int curlen;                /* length of current code */

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

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

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

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

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

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

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

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

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

             continue;

         } else if (count < min_count) {

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

         } else if (curlen != 0) {

             if (curlen != prevlen) {

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

             }

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

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

         } else if (count <= 10) {

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

         } else {

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

         }

         count = 0; prevlen = curlen;

         if (nextlen == 0) {

             max_count = 138, min_count = 3;

         } else if (curlen == nextlen) {

             max_count = 6, min_count = 3;

         } else {

             max_count = 7, min_count = 4;

         }

     }

 }

 /* ===========================================================================

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

  * bl_order of the last bit length code to send.

  */

 local int build_bl_tree(s)

     deflate_state *s;

 {

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