code: 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));
    }
  }
docs: /* ===========================================================================
  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.