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

 * Copyright (C) 1995-2002 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: trees.c,v 1.1 2003-03-24 11:13:44 pj Exp $ */

/* #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) cprintf("\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 */

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

/* 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 (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) (MAX(s->depth[n], s->depth[m]) + 1);

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

#ifdef DUMP_BL_TREE

        if (tree == s->bl_tree) {

            cprintf("\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.