/*
 *  call-seq:
 *     dtable.rotate_cw90  -> a_dtable
 *  
 *  Returns a copy of _dtable_ rotated 90 degrees clockwise.
 */ VALUE dtable_rotate_cw90(VALUE ary)
{
   Dtable *d = Get_Dtable(ary);
   int i, j, num_cols = d->num_cols, num_rows = d->num_rows, last_row = num_rows - 1;
   VALUE new = dtable_init(dtable_alloc(cDtable), num_rows, num_cols);
   Dtable *d2 = Get_Dtable(new);
   double **src, **dest;
   src = d->ptr; dest = d2->ptr;
   for (i = 0; i < num_rows; i++) {
      for (j = 0; j < num_cols; j++) {
         dest[j][last_row-i] = src[i][j];
      }
   }
   return new;
}