ducha-qianduan/node_modules/pako/lib/zlib/trees.js

'use strict';

// (C) 1995-2013 Jean-loup Gailly and Mark Adler
// (C) 2014-2017 Vitaly Puzrin and Andrey Tupitsin
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
//   claim that you wrote the original software. If you use this software
//   in a product, an acknowledgment in the product documentation would be
//   appreciated but is not required.
// 2. Altered source versions must be plainly marked as such, and must not be
//   misrepresented as being the original software.
// 3. This notice may not be removed or altered from any source distribution.

/* eslint-disable space-unary-ops */

var utils = require('../utils/common');

/* Public constants ==========================================================*/
/* ===========================================================================*/


//var Z_FILTERED          = 1;
//var Z_HUFFMAN_ONLY      = 2;
//var Z_RLE               = 3;
var Z_FIXED               = 4;
//var Z_DEFAULT_STRATEGY  = 0;

/* Possible values of the data_type field (though see inflate()) */
var Z_BINARY              = 0;
var Z_TEXT                = 1;
//var Z_ASCII             = 1; // = Z_TEXT
var Z_UNKNOWN             = 2;

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


function zero(buf) { var len = buf.length; while (--len >= 0) { buf[len] = 0; } }

// From zutil.h

var STORED_BLOCK = 0;
var STATIC_TREES = 1;
var DYN_TREES    = 2;
/* The three kinds of block type */

var MIN_MATCH    = 3;
var MAX_MATCH    = 258;
/* The minimum and maximum match lengths */

// From deflate.h
/* ===========================================================================
 * Internal compression state.
 */

var LENGTH_CODES  = 29;
/* number of length codes, not counting the special END_BLOCK code */

var LITERALS      = 256;
/* number of literal bytes 0..255 */

var L_CODES       = LITERALS + 1 + LENGTH_CODES;
/* number of Literal or Length codes, including the END_BLOCK code */

var D_CODES       = 30;
/* number of distance codes */

var BL_CODES      = 19;
/* number of codes used to transfer the bit lengths */

var HEAP_SIZE     = 2 * L_CODES + 1;
/* maximum heap size */

var MAX_BITS      = 15;
/* All codes must not exceed MAX_BITS bits */

var Buf_size      = 16;
/* size of bit buffer in bi_buf */


/* ===========================================================================
 * Constants
 */

var MAX_BL_BITS = 7;
/* Bit length codes must not exceed MAX_BL_BITS bits */

var END_BLOCK   = 256;
/* end of block literal code */

var REP_3_6     = 16;
/* repeat previous bit length 3-6 times (2 bits of repeat count) */

var REPZ_3_10   = 17;
/* repeat a zero length 3-10 times  (3 bits of repeat count) */

var REPZ_11_138 = 18;
/* repeat a zero length 11-138 times  (7 bits of repeat count) */

/* eslint-disable comma-spacing,array-bracket-spacing */
var extra_lbits =   /* 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];

var extra_dbits =   /* 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];

var extra_blbits =  /* 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];

var bl_order =
  [16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15];
/* eslint-enable comma-spacing,array-bracket-spacing */

/* 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.
 */

// We pre-fill arrays with 0 to avoid uninitialized gaps

var DIST_CODE_LEN = 512; /* see definition of array dist_code below */

// !!!! Use flat array instead of structure, Freq = i*2, Len = i*2+1
var static_ltree  = new Array((L_CODES + 2) * 2);
zero(static_ltree);
/* 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).
 */

var static_dtree  = new Array(D_CODES * 2);
zero(static_dtree);
/* The static distance tree. (Actually a trivial tree since all codes use
 * 5 bits.)
 */

var _dist_code    = new Array(DIST_CODE_LEN);
zero(_dist_code);
/* 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.
 */

var _length_code  = new Array(MAX_MATCH - MIN_MATCH + 1);
zero(_length_code);
/* length code for each normalized match length (0 == MIN_MATCH) */

var base_length   = new Array(LENGTH_CODES);
zero(base_length);
/* First normalized length for each code (0 = MIN_MATCH) */

var base_dist     = new Array(D_CODES);
zero(base_dist);
/* First normalized distance for each code (0 = distance of 1) */


function StaticTreeDesc(static_tree, extra_bits, extra_base, elems, max_length) {

  this.static_tree  = static_tree;  /* static tree or NULL */
  this.extra_bits   = extra_bits;   /* extra bits for each code or NULL */
  this.extra_base   = extra_base;   /* base index for extra_bits */
  this.elems        = elems;        /* max number of elements in the tree */
  this.max_length   = max_length;   /* max bit length for the codes */

  // show if `static_tree` has data or dummy - needed for monomorphic objects
  this.has_stree    = static_tree && static_tree.length;
}


var static_l_desc;
var static_d_desc;
var static_bl_desc;


function TreeDesc(dyn_tree, stat_desc) {
  this.dyn_tree = dyn_tree;     /* the dynamic tree */
  this.max_code = 0;            /* largest code with non zero frequency */
  this.stat_desc = stat_desc;   /* the corresponding static tree */
}



function d_code(dist) {
  return dist < 256 ? _dist_code[dist] : _dist_code[256 + (dist >>> 7)];
}


/* ===========================================================================
 * Output a short LSB first on the stream.
 * IN assertion: there is enough room in pendingBuf.
 */
function put_short(s, w) {
//    put_byte(s, (uch)((w) & 0xff));
//    put_byte(s, (uch)((ush)(w) >> 8));
  s.pending_buf[s.pending++] = (w) & 0xff;
  s.pending_buf[s.pending++] = (w >>> 8) & 0xff;
}


/* ===========================================================================
 * Send a value on a given number of bits.
 * IN assertion: length <= 16 and value fits in length bits.
 */
function send_bits(s, value, length) {
  if (s.bi_valid > (Buf_size - length)) {
    s.bi_buf |= (value << s.bi_valid) & 0xffff;
    put_short(s, s.bi_buf);
    s.bi_buf = value >> (Buf_size - s.bi_valid);
    s.bi_valid += length - Buf_size;
  } else {
    s.bi_buf |= (value << s.bi_valid) & 0xffff;
    s.bi_valid += length;
  }
}


function send_code(s, c, tree) {
  send_bits(s, tree[c * 2]/*.Code*/, tree[c * 2 + 1]/*.Len*/);
}


/* ===========================================================================
 * Reverse the first len bits of a code, using straightforward code (a faster
 * method would use a table)
 * IN assertion: 1 <= len <= 15
 */
function bi_reverse(code, len) {
  var 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.
 */
function bi_flush(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) {
    s.pending_buf[s.pending++] = s.bi_buf & 0xff;
    s.bi_buf >>= 8;
    s.bi_valid -= 8;
  }
}


/* ===========================================================================
 * 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.
 */
function gen_bitlen(s, desc)
//    deflate_state *s;
//    tree_desc *desc;    /* the tree descriptor */
{
  var tree            = desc.dyn_tree;
  var max_code        = desc.max_code;
  var stree           = desc.stat_desc.static_tree;
  var has_stree       = desc.stat_desc.has_stree;
  var extra           = desc.stat_desc.extra_bits;
  var base            = desc.stat_desc.extra_base;
  var max_length      = desc.stat_desc.max_length;
  var h;              /* heap index */
  var n, m;           /* iterate over the tree elements */
  var bits;           /* bit length */
  var xbits;          /* extra bits */
  var f;              /* frequency */
  var 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] * 2 + 1]/*.Len*/ = 0; /* root of the heap */

  for (h = s.heap_max + 1; h < HEAP_SIZE; h++) {
    n = s.heap[h];
    bits = tree[tree[n * 2 + 1]/*.Dad*/ * 2 + 1]/*.Len*/ + 1;
    if (bits > max_length) {
      bits = max_length;
      overflow++;
    }
    tree[n * 2 + 1]/*.Len*/ = 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 * 2]/*.Freq*/;
    s.opt_len += f * (bits + xbits);
    if (has_stree) {
      s.static_len += f * (stree[n * 2 + 1]/*.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 * 2 + 1]/*.Len*/ !== bits) {
        // Trace((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));
        s.opt_len += (bits - tree[m * 2 + 1]/*.Len*/) * tree[m * 2]/*.Freq*/;
        tree[m * 2 + 1]/*.Len*/ = 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.
 */
function 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 */
{
  var next_code = new Array(MAX_BITS + 1); /* next code value for each bit length */
  var code = 0;              /* running code value */
  var bits;                  /* bit index */
  var 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++) {
    var len = tree[n * 2 + 1]/*.Len*/;
    if (len === 0) { continue; }
    /* Now reverse the bits */
    tree[n * 2]/*.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));
  }
}


/* ===========================================================================
 * Initialize the various 'constant' tables.
 */
function tr_static_init() {
  var n;        /* iterates over tree elements */
  var bits;     /* bit counter */
  var length;   /* length value */
  var code;     /* code value */
  var dist;     /* distance index */
  var bl_count = new Array(MAX_BITS + 1);
  /* number of codes at each bit length for an optimal tree */

  // do check in _tr_init()
  //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++] = 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] = 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++] = 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++] = 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 * 2 + 1]/*.Len*/ = 8;
    n++;
    bl_count[8]++;
  }
  while (n <= 255) {
    static_ltree[n * 2 + 1]/*.Len*/ = 9;
    n++;
    bl_count[9]++;
  }
  while (n <= 279) {
    static_ltree[n * 2 + 1]/*.Len*/ = 7;
    n++;
    bl_count[7]++;
  }
  while (n <= 287) {
    static_ltree[n * 2 + 1]/*.Len*/ = 8;
    n++;
    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(static_ltree, L_CODES + 1, bl_count);

  /* The static distance tree is trivial: */
  for (n = 0; n < D_CODES; n++) {
    static_dtree[n * 2 + 1]/*.Len*/ = 5;
    static_dtree[n * 2]/*.Code*/ = bi_reverse(n, 5);
  }

  // Now data ready and we can init static trees
  static_l_desc = new StaticTreeDesc(static_ltree, extra_lbits, LITERALS + 1, L_CODES, MAX_BITS);
  static_d_desc = new StaticTreeDesc(static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS);
  static_bl_desc = new StaticTreeDesc(new Array(0), extra_blbits, 0,         BL_CODES, MAX_BL_BITS);

  //static_init_done = true;
}


/* ===========================================================================
 * Initialize a new block.
 */
function init_block(s) {
  var n; /* iterates over tree elements */

  /* Initialize the trees. */
  for (n = 0; n < L_CODES;  n++) { s.dyn_ltree[n * 2]/*.Freq*/ = 0; }
  for (n = 0; n < D_CODES;  n++) { s.dyn_dtree[n * 2]/*.Freq*/ = 0; }
  for (n = 0; n < BL_CODES; n++) { s.bl_tree[n * 2]/*.Freq*/ = 0; }

  s.dyn_ltree[END_BLOCK * 2]/*.Freq*/ = 1;
  s.opt_len = s.static_len = 0;
  s.last_lit = s.matches = 0;
}


/* ===========================================================================
 * Flush the bit buffer and align the output on a byte boundary
 */
function bi_windup(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.pending_buf[s.pending++] = s.bi_buf;
  }
  s.bi_buf = 0;
  s.bi_valid = 0;
}

/* ===========================================================================
 * Copy a stored block, storing first the length and its
 * one's complement if requested.
 */
function copy_block(s, buf, len, header)
//DeflateState *s;
//charf    *buf;    /* the input data */
//unsigned len;     /* its length */
//int      header;  /* true if block header must be written */
{
  bi_windup(s);        /* align on byte boundary */

  if (header) {
    put_short(s, len);
    put_short(s, ~len);
  }
//  while (len--) {
//    put_byte(s, *buf++);
//  }
  utils.arraySet(s.pending_buf, s.window, buf, len, s.pending);
  s.pending += len;
}

/* ===========================================================================
 * Compares to subtrees, using the tree depth as tie breaker when
 * the subtrees have equal frequency. This minimizes the worst case length.
 */
function smaller(tree, n, m, depth) {
  var _n2 = n * 2;
  var _m2 = m * 2;
  return (tree[_n2]/*.Freq*/ < tree[_m2]/*.Freq*/ ||
         (tree[_n2]/*.Freq*/ === tree[_m2]/*.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).
 */
function pqdownheap(s, tree, k)
//    deflate_state *s;
//    ct_data *tree;  /* the tree to restore */
//    int k;               /* node to move down */
{
  var v = s.heap[k];
  var 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;
}


// inlined manually
// var SMALLEST = 1;

/* ===========================================================================
 * Send the block data compressed using the given Huffman trees
 */
function compress_block(s, ltree, dtree)
//    deflate_state *s;
//    const ct_data *ltree; /* literal tree */
//    const ct_data *dtree; /* distance tree */
{
  var dist;           /* distance of matched string */
  var lc;             /* match length or unmatched char (if dist == 0) */
  var lx = 0;         /* running index in l_buf */
  var code;           /* the code to send */
  var extra;          /* number of extra bits to send */

  if (s.last_lit !== 0) {
    do {
      dist = (s.pending_buf[s.d_buf + lx * 2] << 8) | (s.pending_buf[s.d_buf + lx * 2 + 1]);
      lc = s.pending_buf[s.l_buf + lx];
      lx++;

      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 the 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 -= base_dist[code];
          send_bits(s, dist, extra);   /* send the extra distance bits */
        }
      } /* literal or match pair ? */

      /* Check that the overlay between pending_buf and d_buf+l_buf is ok: */
      //Assert((uInt)(s->pending) < s->lit_bufsize + 2*lx,
      //       "pendingBuf overflow");

    } while (lx < s.last_lit);
  }

  send_code(s, END_BLOCK, ltree);
}


/* ===========================================================================
 * 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.
 */
function build_tree(s, desc)
//    deflate_state *s;
//    tree_desc *desc; /* the tree descriptor */
{
  var tree     = desc.dyn_tree;
  var stree    = desc.stat_desc.static_tree;
  var has_stree = desc.stat_desc.has_stree;
  var elems    = desc.stat_desc.elems;
  var n, m;          /* iterate over heap elements */
  var max_code = -1; /* largest code with non zero frequency */
  var 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 * 2]/*.Freq*/ !== 0) {
      s.heap[++s.heap_len] = max_code = n;
      s.depth[n] = 0;

    } else {
      tree[n * 2 + 1]/*.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 * 2]/*.Freq*/ = 1;
    s.depth[node] = 0;
    s.opt_len--;

    if (has_stree) {
      s.static_len -= stree[node * 2 + 1]/*.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 >> 1/*int /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 */
    /*** pqremove ***/
    n = s.heap[1/*SMALLEST*/];
    s.heap[1/*SMALLEST*/] = s.heap[s.heap_len--];
    pqdownheap(s, tree, 1/*SMALLEST*/);
    /***/

    m = s.heap[1/*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 * 2]/*.Freq*/ = tree[n * 2]/*.Freq*/ + tree[m * 2]/*.Freq*/;
    s.depth[node] = (s.depth[n] >= s.depth[m] ? s.depth[n] : s.depth[m]) + 1;
    tree[n * 2 + 1]/*.Dad*/ = tree[m * 2 + 1]/*.Dad*/ = node;

    /* and insert the new node in the heap */
    s.heap[1/*SMALLEST*/] = node++;
    pqdownheap(s, tree, 1/*SMALLEST*/);

  } while (s.heap_len >= 2);

  s.heap[--s.heap_max] = s.heap[1/*SMALLEST*/];

  /* At this point, the fields freq and dad are set. We can now
   * generate the bit lengths.
   */
  gen_bitlen(s, desc);

  /* The field len is now set, we can generate the bit codes */
  gen_codes(tree, max_code, s.bl_count);
}


/* ===========================================================================
 * Scan a literal or distance tree to determine the frequencies of the codes
 * in the bit length tree.
 */
function 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 */
{
  var n;                     /* iterates over all tree elements */
  var prevlen = -1;          /* last emitted length */
  var curlen;                /* length of current code */

  var nextlen = tree[0 * 2 + 1]/*.Len*/; /* length of next code */

  var count = 0;             /* repeat count of the current code */
  var max_count = 7;         /* max repeat count */
  var min_count = 4;         /* min repeat count */

  if (nextlen === 0) {
    max_count = 138;
    min_count = 3;
  }
  tree[(max_code + 1) * 2 + 1]/*.Len*/ = 0xffff; /* guard */

  for (n = 0; n <= max_code; n++) {
    curlen = nextlen;
    nextlen = tree[(n + 1) * 2 + 1]/*.Len*/;

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

    } else if (count < min_count) {
      s.bl_tree[curlen * 2]/*.Freq*/ += count;

    } else if (curlen !== 0) {

      if (curlen !== prevlen) { s.bl_tree[curlen * 2]/*.Freq*/++; }
      s.bl_tree[REP_3_6 * 2]/*.Freq*/++;

    } else if (count <= 10) {
      s.bl_tree[REPZ_3_10 * 2]/*.Freq*/++;

    } else {
      s.bl_tree[REPZ_11_138 * 2]/*.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.
 */
function 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 */
{
  var n;                     /* iterates over all tree elements */
  var prevlen = -1;          /* last emitted length */
  var curlen;                /* length of current code */

  var nextlen = tree[0 * 2 + 1]/*.Len*/; /* length of next code */

  var count = 0;             /* repeat count of the current code */
  var max_count = 7;         /* max repeat count */
  var 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) * 2 + 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.
 */
function build_bl_tree(s) {
  var 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, s.dyn_ltree, s.l_desc.max_code);
  scan_tree(s, s.dyn_dtree, s.d_desc.max_code);

  /* Build the bit length tree: */
  build_tree(s, 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] * 2 + 1]/*.Len*/ !== 0) {
      break;
    }
  }
  /* Update opt_len to include the bit length tree and counts */
  s.opt_len += 3 * (max_blindex + 1) + 5 + 5 + 4;
  //Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld",
  //        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.
 */
function send_all_trees(s, lcodes, dcodes, blcodes)
//    deflate_state *s;
//    int lcodes, dcodes, blcodes; /* number of codes for each tree */
{
  var 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] * 2 + 1]/*.Len*/, 3);
  }
  //Tracev((stderr, "\nbl tree: sent %ld", s->bits_sent));

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

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


/* ===========================================================================
 * 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
 *       "black list" (0..6, 14..25, 28..31).
 *    b) There is at least one printable character belonging to the
 *       "white 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.
 */
function detect_data_type(s) {
  /* black_mask is the bit mask of black-listed bytes
   * set bits 0..6, 14..25, and 28..31
   * 0xf3ffc07f = binary 11110011111111111100000001111111
   */
  var black_mask = 0xf3ffc07f;
  var n;

  /* Check for non-textual ("black-listed") bytes. */
  for (n = 0; n <= 31; n++, black_mask >>>= 1) {
    if ((black_mask & 1) && (s.dyn_ltree[n * 2]/*.Freq*/ !== 0)) {
      return Z_BINARY;
    }
  }

  /* Check for textual ("white-listed") bytes. */
  if (s.dyn_ltree[9 * 2]/*.Freq*/ !== 0 || s.dyn_ltree[10 * 2]/*.Freq*/ !== 0 ||
      s.dyn_ltree[13 * 2]/*.Freq*/ !== 0) {
    return Z_TEXT;
  }
  for (n = 32; n < LITERALS; n++) {
    if (s.dyn_ltree[n * 2]/*.Freq*/ !== 0) {
      return Z_TEXT;
    }
  }

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


var static_init_done = false;

/* ===========================================================================
 * Initialize the tree data structures for a new zlib stream.
 */
function _tr_init(s)
{

  if (!static_init_done) {
    tr_static_init();
    static_init_done = true;
  }

  s.l_desc  = new TreeDesc(s.dyn_ltree, static_l_desc);
  s.d_desc  = new TreeDesc(s.dyn_dtree, static_d_desc);
  s.bl_desc = new TreeDesc(s.bl_tree, static_bl_desc);

  s.bi_buf = 0;
  s.bi_valid = 0;

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


/* ===========================================================================
 * Send a stored block
 */
function _tr_stored_block(s, buf, stored_len, last)
//DeflateState *s;
//charf *buf;       /* input block */
//ulg stored_len;   /* length of input block */
//int last;         /* one if this is the last block for a file */
{
  send_bits(s, (STORED_BLOCK << 1) + (last ? 1 : 0), 3);    /* send block type */
  copy_block(s, buf, stored_len, true); /* with header */
}


/* ===========================================================================
 * Send one empty static block to give enough lookahead for inflate.
 * This takes 10 bits, of which 7 may remain in the bit buffer.
 */
function _tr_align(s) {
  send_bits(s, STATIC_TREES << 1, 3);
  send_code(s, END_BLOCK, static_ltree);
  bi_flush(s);
}


/* ===========================================================================
 * Determine the best encoding for the current block: dynamic trees, static
 * trees or store, and output the encoded block to the zip file.
 */
function _tr_flush_block(s, buf, stored_len, last)
//DeflateState *s;
//charf *buf;       /* input block, or NULL if too old */
//ulg stored_len;   /* length of input block */
//int last;         /* one if this is the last block for a file */
{
  var opt_lenb, static_lenb;  /* opt_len and static_len in bytes */
  var 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, s.l_desc);
    // Tracev((stderr, "\nlit data: dyn %ld, stat %ld", s->opt_len,
    //        s->static_len));

    build_tree(s, s.d_desc);
    // Tracev((stderr, "\ndist data: dyn %ld, stat %ld", 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->last_lit));

    if (static_lenb <= opt_lenb) { opt_lenb = static_lenb; }

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

  if ((stored_len + 4 <= opt_lenb) && (buf !== -1)) {
    /* 4: two words for the lengths */

    /* 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 (s.strategy === Z_FIXED || static_lenb === opt_lenb) {

    send_bits(s, (STATIC_TREES << 1) + (last ? 1 : 0), 3);
    compress_block(s, static_ltree, static_dtree);

  } else {
    send_bits(s, (DYN_TREES << 1) + (last ? 1 : 0), 3);
    send_all_trees(s, s.l_desc.max_code + 1, s.d_desc.max_code + 1, max_blindex + 1);
    compress_block(s, s.dyn_ltree, s.dyn_dtree);
  }
  // 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);
  }
  // Tracev((stderr,"\ncomprlen %lu(%lu) ", s->compressed_len>>3,
  //       s->compressed_len-7*last));
}

/* ===========================================================================
 * Save the match info and tally the frequency counts. Return true if
 * the current block must be flushed.
 */
function _tr_tally(s, dist, lc)
//    deflate_state *s;
//    unsigned dist;  /* distance of matched string */
//    unsigned lc;    /* match length-MIN_MATCH or unmatched char (if dist==0) */
{
  //var out_length, in_length, dcode;

  s.pending_buf[s.d_buf + s.last_lit * 2]     = (dist >>> 8) & 0xff;
  s.pending_buf[s.d_buf + s.last_lit * 2 + 1] = dist & 0xff;

  s.pending_buf[s.l_buf + s.last_lit] = lc & 0xff;
  s.last_lit++;

  if (dist === 0) {
    /* lc is the unmatched char */
    s.dyn_ltree[lc * 2]/*.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) * 2]/*.Freq*/++;
    s.dyn_dtree[d_code(dist) * 2]/*.Freq*/++;
  }

// (!) This block is disabled in zlib defaults,
// don't enable it for binary compatibility

//#ifdef TRUNCATE_BLOCK
//  /* Try to guess if it is profitable to stop the current block here */
//  if ((s.last_lit & 0x1fff) === 0 && s.level > 2) {
//    /* Compute an upper bound for the compressed length */
//    out_length = s.last_lit*8;
//    in_length = s.strstart - s.block_start;
//
//    for (dcode = 0; dcode < D_CODES; dcode++) {
//      out_length += s.dyn_dtree[dcode*2]/*.Freq*/ * (5 + extra_dbits[dcode]);
//    }
//    out_length >>>= 3;
//    //Tracev((stderr,"\nlast_lit %u, in %ld, out ~%ld(%ld%%) ",
//    //       s->last_lit, in_length, out_length,
//    //       100L - out_length*100L/in_length));
//    if (s.matches < (s.last_lit>>1)/*int /2*/ && out_length < (in_length>>1)/*int /2*/) {
//      return true;
//    }
//  }
//#endif

  return (s.last_lit === s.lit_bufsize - 1);
  /* We avoid equality with lit_bufsize because of wraparound at 64K
   * on 16 bit machines and because stored blocks are restricted to
   * 64K-1 bytes.
   */
}

exports._tr_init  = _tr_init;
exports._tr_stored_block = _tr_stored_block;
exports._tr_flush_block  = _tr_flush_block;
exports._tr_tally = _tr_tally;
exports._tr_align = _tr_align;