File Coverage

trees.c

Criterion	Covered	Total	%
statement	269	304	88.4
branch	180	224	80.3
condition			n/a
subroutine			n/a
pod			n/a
total	449	528	85.0

/* trees.c -- output deflated data using Huffman coding
  * Copyright (C) 1995-2026 Jean-loup Gailly
  * detect_data_type() function provided freely by Cosmin Truta, 2006
  * 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 ZLIB_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.
 */

/* ===========================================================================
 * 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 /* defined(GEN_TREES_H) || !defined(STDC) */

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 */
};

#ifdef NO_INIT_GLOBAL_POINTERS
#  define TCONST
#else
#  define TCONST const
#endif

local TCONST static_tree_desc static_l_desc =
{static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS};

local TCONST static_tree_desc static_d_desc =
{static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS};

local TCONST static_tree_desc static_bl_desc =
{(const ct_data *)0, extra_blbits, 0,   BL_CODES, MAX_BL_BITS};

/* ===========================================================================
  * 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)); \
}

/* ===========================================================================
  * Reverse the first len bits of a code, using straightforward code (a faster
 * method would use a table)
 * IN assertion: 1 <= len <= 15
 */
local unsigned bi_reverse(unsigned code, int len) {
        unsigned res = 0;
        do {
                res |= code & 1;
                code >>= 1, res <<= 1;
        } while (--len > 0);
        return res >> 1;
}

/* ===========================================================================
 * Flush the bit buffer, keeping at most 7 bits in it.
 */
local void bi_flush(deflate_state *s) {
    if (s->bi_valid == 16) {
                put_short(s, s->bi_buf);
                s->bi_buf = 0;
        s->bi_valid = 0;
        } else if (s->bi_valid >= 8) {
                put_byte(s, (Byte)s->bi_buf);
        s->bi_buf >>= 8;
                s->bi_valid -= 8;
    }
}

/* ===========================================================================
  * Flush the bit buffer and align the output on a byte boundary
  */
local void bi_windup(deflate_state *s) {
    if (s->bi_valid > 8) {
                put_short(s, s->bi_buf);
        } else if (s->bi_valid > 0) {
        put_byte(s, (Byte)s->bi_buf);
        }
        s->bi_used = ((s->bi_valid - 1) & 7) + 1;
        s->bi_buf = 0;
        s->bi_valid = 0;
#ifdef ZLIB_DEBUG
        s->bits_sent = (s->bits_sent + 7) & ~(ulg)7;
#endif
}

/* ===========================================================================
  * 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(ct_data *tree, int max_code, ushf *bl_count) {
    ush next_code[MAX_BITS+1]; /* next code value for each bit length */
    unsigned 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++) {
        code = (code + bl_count[bits - 1]) << 1;
        next_code[bits] = (ush)code;
    }
    /* 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 = (ush)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));
    }
}

#ifdef GEN_TREES_H
local void gen_trees_header(void);
#endif

#ifndef ZLIB_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 /* !ZLIB_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

/* ===========================================================================
  * Send a value on a given number of bits.
  * IN assertion: length <= 16 and value fits in length bits.
  */
#ifdef ZLIB_DEBUG
local void send_bits(deflate_state *s, int value, int length) {
    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 |= (ush)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 |= (ush)value << s->bi_valid;
                s->bi_valid += length;
    }
}
#else /* !ZLIB_DEBUG */

#define send_bits(s, value, length) \
{ int len = length;\
  if (s->bi_valid > (int)Buf_size - len) {\
        int val = (int)value;\
        s->bi_buf |= (ush)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 |= (ush)(value) << s->bi_valid;\
        s->bi_valid += len;\
  }\
}
#endif /* ZLIB_DEBUG */


/* the arguments must not have side effects */

/* ===========================================================================
 * Initialize the various 'constant' tables.
 */
local void tr_static_init(void) {
#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: */
#ifdef NO_INIT_GLOBAL_POINTERS
    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;
#endif

    /* 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) */
}

/* ===========================================================================
  * Generate the file trees.h describing the static trees.
  */
#ifdef GEN_TREES_H
#  ifndef ZLIB_DEBUG
#    include <stdio.h>
#  endif

#  define SEPARATOR(i, last, width) \
      ((i) == (last)? "\n};\n\n" :    \
       ((i) % (width) == (width) - 1 ? ",\n" : ", "))

void gen_trees_header(void) {
    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 ZLIB_INTERNAL _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 ZLIB_INTERNAL _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 a new block.
  */
local void init_block(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->sym_next = s->matches = 0;
}

/* ===========================================================================
  * Initialize the tree data structures for a new zlib stream.
  */
void ZLIB_INTERNAL _tr_init(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->bi_used = 0;
#ifdef ZLIB_DEBUG
        s->compressed_len = 0L;
    s->bits_sent = 0L;
#endif

        /* Initialize the first block of the first file: */
        init_block(s);
}

#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(deflate_state *s, ct_data *tree, int k) {
        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(deflate_state *s, tree_desc *desc) {
        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 * (unsigned)(bits + xbits);
                if (stree) s->static_len += (ulg)f * (unsigned)(stree[n].Len + xbits);
        }
        if (overflow == 0) return;

        Tracev((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) {
                                Tracev((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));
                                s->opt_len += ((ulg)bits - tree[m].Len) * tree[m].Freq;
                                tree[m].Len = (ush)bits;
                        }
                        n--;
                }
        }
}

#ifdef DUMP_BL_TREE
#  include <stdio.h>
#endif

/* ===========================================================================
  * 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(deflate_state *s, tree_desc *desc) {
        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(deflate_state *s, ct_data *tree, int max_code) {
        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 += (ush)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(deflate_state *s, ct_data *tree, int max_code) {
        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(deflate_state *s) {
        int max_blindex;  /* index of last bit length code of non zero freq */

        /* Determine the bit length frequencies for literal and distance trees */
        scan_tree(s, (ct_data *)s->dyn_ltree, s->l_desc.max_code);
        scan_tree(s, (ct_data *)s->dyn_dtree, s->d_desc.max_code);

        /* Build the bit length tree: */
        build_tree(s, (tree_desc *)(&(s->bl_desc)));
        /* opt_len now includes the length of the tree representations, except the
          * lengths of the bit lengths codes and the 5 + 5 + 4 bits for the counts.
          */

        /* Determine the number of bit length codes to send. The pkzip format
          * requires that at least 4 bit length codes be sent. (appnote.txt says
          * 3 but the actual value used is 4.)
          */
        for (max_blindex = BL_CODES-1; max_blindex >= 3; max_blindex--) {
                if (s->bl_tree[bl_order[max_blindex]].Len != 0) break;
        }
        /* Update opt_len to include the bit length tree and counts */
        s->opt_len += 3*((ulg)max_blindex + 1) + 5 + 5 + 4;
        Tracev((stderr, "\ndyn trees: dyn %lu, stat %lu",
                        s->opt_len, s->static_len));

        return max_blindex;
}

/* ===========================================================================
  * Send the header for a block using dynamic Huffman trees: the counts, the
  * lengths of the bit length codes, the literal tree and the distance tree.
  * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
  */
local void send_all_trees(deflate_state *s, int lcodes, int dcodes,
                                                    int blcodes) {
        int rank;                    /* index in bl_order */

        Assert (lcodes >= 257 && dcodes >= 1 && blcodes >= 4, "not enough codes");
        Assert (lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
                        "too many codes");
        Tracev((stderr, "\nbl counts: "));
        send_bits(s, lcodes - 257, 5);  /* not +255 as stated in appnote.txt */
        send_bits(s, dcodes - 1,   5);
        send_bits(s, blcodes - 4,  4);  /* not -3 as stated in appnote.txt */
        for (rank = 0; rank < blcodes; rank++) {
                Tracev((stderr, "\nbl code %2d ", bl_order[rank]));
                send_bits(s, s->bl_tree[bl_order[rank]].Len, 3);
        }
        Tracev((stderr, "\nbl tree: sent %lu", s->bits_sent));

        send_tree(s, (ct_data *)s->dyn_ltree, lcodes - 1);  /* literal tree */
        Tracev((stderr, "\nlit tree: sent %lu", s->bits_sent));

        send_tree(s, (ct_data *)s->dyn_dtree, dcodes - 1);  /* distance tree */
        Tracev((stderr, "\ndist tree: sent %lu", s->bits_sent));
}

/* ===========================================================================
  * Send a stored block
  */
void ZLIB_INTERNAL _tr_stored_block(deflate_state *s, charf *buf,
                                                                        ulg stored_len, int last) {
        send_bits(s, (STORED_BLOCK<<1) + last, 3);  /* send block type */
        bi_windup(s);        /* align on byte boundary */
        put_short(s, (ush)stored_len);
        put_short(s, (ush)~stored_len);
        if (stored_len)
                zmemcpy(s->pending_buf + s->pending, (Bytef *)buf, stored_len);
        s->pending += stored_len;
#ifdef ZLIB_DEBUG
        s->compressed_len = (s->compressed_len + 3 + 7) & (ulg)~7L;
        s->compressed_len += (stored_len + 4) << 3;
        s->bits_sent += 2*16;
        s->bits_sent += stored_len << 3;
#endif
}

/* ===========================================================================
  * Flush the bits in the bit buffer to pending output (leaves at most 7 bits)
  */
void ZLIB_INTERNAL _tr_flush_bits(deflate_state *s) {
        bi_flush(s);
}

/* ===========================================================================
  * Send one empty static block to give enough lookahead for inflate.
  * This takes 10 bits, of which 7 may remain in the bit buffer.
  */
void ZLIB_INTERNAL _tr_align(deflate_state *s) {
        send_bits(s, STATIC_TREES<<1, 3);
        send_code(s, END_BLOCK, static_ltree);
#ifdef ZLIB_DEBUG
        s->compressed_len += 10L; /* 3 for block type, 7 for EOB */
#endif
        bi_flush(s);
}

/* ===========================================================================
  * Send the block data compressed using the given Huffman trees
  */
local void compress_block(deflate_state *s, const ct_data *ltree,
                                                    const ct_data *dtree) {
        unsigned dist;      /* distance of matched string */
        int lc;             /* match length or unmatched char (if dist == 0) */
        unsigned sx = 0;    /* running index in symbol buffers */
        unsigned code;      /* the code to send */
        int extra;          /* number of extra bits to send */

        if (s->sym_next != 0) do {
#ifdef LIT_MEM
                dist = s->d_buf[sx];
                lc = s->l_buf[sx++];
#else
                dist = s->sym_buf[sx++] & 0xff;
                dist += (unsigned)(s->sym_buf[sx++] & 0xff) << 8;
                lc = s->sym_buf[sx++];
#endif
                if (dist == 0) {
                        send_code(s, lc, ltree); /* send a literal byte */
                        Tracecv(isgraph(lc), (stderr," '%c' ", lc));
                } else {
                        /* Here, lc is the match length - MIN_MATCH */
                        code = _length_code[lc];
                        send_code(s, code + LITERALS + 1, ltree);   /* send length code */
                        extra = extra_lbits[code];
                        if (extra != 0) {
                                lc -= base_length[code];
                                send_bits(s, lc, extra);       /* send the extra length bits */
                        }
                        dist--; /* dist is now the match distance - 1 */
                        code = d_code(dist);
                        Assert (code < D_CODES, "bad d_code");

                        send_code(s, code, dtree);       /* send the distance code */
                        extra = extra_dbits[code];
                        if (extra != 0) {
                                dist -= (unsigned)base_dist[code];
                                send_bits(s, (int)dist, extra); /* send the extra bits */
                        }
                } /* literal or match pair ? */

                /* Check for no overlay of pending_buf on needed symbols */
#ifdef LIT_MEM
                Assert(s->pending < 2 * (s->lit_bufsize + sx), "pendingBuf overflow");
#else
                Assert(s->pending < s->lit_bufsize + sx, "pendingBuf overflow");
#endif

        } while (sx < s->sym_next);

        send_code(s, END_BLOCK, ltree);
}

/* ===========================================================================
  * Check if the data type is TEXT or BINARY, using the following algorithm:
  * - TEXT if the two conditions below are satisfied:
  *    a) There are no non-portable control characters belonging to the
  *       "block list" (0..6, 14..25, 28..31).
  *    b) There is at least one printable character belonging to the
  *       "allow list" (9 {TAB}, 10 {LF}, 13 {CR}, 32..255).
  * - BINARY otherwise.
  * - The following partially-portable control characters form a
  *   "gray list" that is ignored in this detection algorithm:
  *   (7 {BEL}, 8 {BS}, 11 {VT}, 12 {FF}, 26 {SUB}, 27 {ESC}).
  * IN assertion: the fields Freq of dyn_ltree are set.
  */
local int detect_data_type(deflate_state *s) {
        /* block_mask is the bit mask of block-listed bytes
          * set bits 0..6, 14..25, and 28..31
          * 0xf3ffc07f = binary 11110011111111111100000001111111
          */
        unsigned long block_mask = 0xf3ffc07fUL;
        int n;

        /* Check for non-textual ("block-listed") bytes. */
        for (n = 0; n <= 31; n++, block_mask >>= 1)
                if ((block_mask & 1) && (s->dyn_ltree[n].Freq != 0))
                        return Z_BINARY;

        /* Check for textual ("allow-listed") bytes. */
        if (s->dyn_ltree[9].Freq != 0 || s->dyn_ltree[10].Freq != 0
                        || s->dyn_ltree[13].Freq != 0)
                return Z_TEXT;
        for (n = 32; n < LITERALS; n++)
                if (s->dyn_ltree[n].Freq != 0)
                        return Z_TEXT;

        /* There are no "block-listed" or "allow-listed" bytes:
          * this stream either is empty or has tolerated ("gray-listed") bytes only.
          */
        return Z_BINARY;
}

/* ===========================================================================
  * Determine the best encoding for the current block: dynamic trees, static
  * trees or store, and write out the encoded block.
  */
void ZLIB_INTERNAL _tr_flush_block(deflate_state *s, charf *buf,
                                                                      ulg stored_len, int last) {
        ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
        int max_blindex = 0;  /* index of last bit length code of non zero freq */

        /* Build the Huffman trees unless a stored block is forced */
        if (s->level > 0) {

                /* Check if the file is binary or text */
                if (s->strm->data_type == Z_UNKNOWN)
                        s->strm->data_type = detect_data_type(s);

                /* Construct the literal and distance trees */
                build_tree(s, (tree_desc *)(&(s->l_desc)));
                Tracev((stderr, "\nlit data: dyn %lu, stat %lu", s->opt_len,
                                s->static_len));

                build_tree(s, (tree_desc *)(&(s->d_desc)));
                Tracev((stderr, "\ndist data: dyn %lu, stat %lu", s->opt_len,
                                s->static_len));
                /* At this point, opt_len and static_len are the total bit lengths of
                  * the compressed block data, excluding the tree representations.
                  */

                /* Build the bit length tree for the above two trees, and get the index
                  * in bl_order of the last bit length code to send.
                  */
                max_blindex = build_bl_tree(s);

                /* Determine the best encoding. Compute the block lengths in bytes. */
                opt_lenb = (s->opt_len + 3 + 7) >> 3;
                static_lenb = (s->static_len + 3 + 7) >> 3;

                Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ",
                                opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len,
                                s->sym_next / 3));

#ifndef FORCE_STATIC
                if (static_lenb <= opt_lenb || s->strategy == Z_FIXED)
#endif
                        opt_lenb = static_lenb;

        } else {
                Assert(buf != (char*)0, "lost buf");
                opt_lenb = static_lenb = stored_len + 5; /* force a stored block */
        }

#ifdef FORCE_STORED
        if (buf != (char*)0) { /* force stored block */
#else
        if (stored_len + 4 <= opt_lenb && buf != (char*)0) {
                                              /* 4: two words for the lengths */
#endif
                /* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
                  * Otherwise we can't have processed more than WSIZE input bytes since
                  * the last block flush, because compression would have been
                  * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
                  * transform a block into a stored block.
                  */
                _tr_stored_block(s, buf, stored_len, last);

        } else if (static_lenb == opt_lenb) {
                send_bits(s, (STATIC_TREES<<1) + last, 3);
                compress_block(s, (const ct_data *)static_ltree,
                                              (const ct_data *)static_dtree);
#ifdef ZLIB_DEBUG
                s->compressed_len += 3 + s->static_len;
#endif
        } else {
                send_bits(s, (DYN_TREES<<1) + last, 3);
                send_all_trees(s, s->l_desc.max_code + 1, s->d_desc.max_code + 1,
                                              max_blindex + 1);
                compress_block(s, (const ct_data *)s->dyn_ltree,
                                              (const ct_data *)s->dyn_dtree);
#ifdef ZLIB_DEBUG
                s->compressed_len += 3 + s->opt_len;
#endif
        }
        Assert (s->compressed_len == s->bits_sent, "bad compressed size");
        /* The above check is made mod 2^32, for files larger than 512 MB
          * and uLong implemented on 32 bits.
          */
        init_block(s);

        if (last) {
                bi_windup(s);
#ifdef ZLIB_DEBUG
                s->compressed_len += 7;  /* align on byte boundary */
#endif
        }
        Tracev((stderr,"\ncomprlen %lu(%lu) ", s->compressed_len >> 3,
                      s->compressed_len - 7*(ulg)last));
}

/* ===========================================================================
  * Save the match info and tally the frequency counts. Return true if
  * the current block must be flushed.
  */
int ZLIB_INTERNAL _tr_tally(deflate_state *s, unsigned dist, unsigned lc) {
#ifdef LIT_MEM
        s->d_buf[s->sym_next] = (ush)dist;
        s->l_buf[s->sym_next++] = (uch)lc;
#else
        s->sym_buf[s->sym_next++] = (uch)dist;
        s->sym_buf[s->sym_next++] = (uch)(dist >> 8);
        s->sym_buf[s->sym_next++] = (uch)lc;
#endif
        if (dist == 0) {
                /* lc is the unmatched char */
                s->dyn_ltree[lc].Freq++;
        } else {
                s->matches++;
                /* Here, lc is the match length - MIN_MATCH */
                dist--;             /* dist = match distance - 1 */
                Assert((ush)dist < (ush)MAX_DIST(s) &&
                              (ush)lc <= (ush)(MAX_MATCH-MIN_MATCH) &&
                              (ush)d_code(dist) < (ush)D_CODES,  "_tr_tally: bad match");

                s->dyn_ltree[_length_code[lc] + LITERALS + 1].Freq++;
                s->dyn_dtree[d_code(dist)].Freq++;
        }
        return (s->sym_next == s->sym_end);
}