Function build_bl_tree

Picviewer CE+/dist.user.js:11261–11289

(s)

 * 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;
}


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