/**************************************************************************
Return the direction that takes us most directly to dest_x,dest_y.
**************************************************************************/
static int straightest_direction(int src_x, int src_y, int dest_x, int dest_y)
{
  static int tx[8] = {
    DIR8_SOUTHEAST, DIR8_EAST,  DIR8_NORTHEAST, DIR8_NORTH,
    DIR8_SOUTHWEST, DIR8_SOUTH, DIR8_NORTHWEST, DIR8_WEST };
  int temp, delta_x, delta_y, nn= 0;

  /* Sanitize */
  normalize_map_pos(&src_x, &src_y);
  normalize_map_pos(&dest_x, &dest_y);

  /* compute sign and magnitude of x delta */
  if( (delta_x= dest_x - src_x) < 0 )
    nn|= 4, delta_x= -delta_x;

  /* if wrapped and closer, flip sign and save new delta */
  if( has_mapwrap(MAP_TYPE_WRAPX) && (temp= map.xsize - delta_x) < delta_x )
    nn^= 4, delta_x= temp;

  /* compute sign and magnitude of y delta */
  if( (delta_y= dest_y - src_y) < 0 )
    nn|= 2, delta_y= -delta_y;

  /* if wrapped and closer, flip sign and save new delta */
  if( has_mapwrap(MAP_TYPE_WRAPY) && (temp= map.ysize - delta_y) < delta_y )
    nn^= 2, delta_y= temp;

  /*
   *  - 3 -   If point is closer to the cardinal axes vs diagonals
   *  7 s 1   then update the index nn using these index positions.
   *  - 5 -   Test for 2 dy < dx (or dy < dx-dy) for cardinal x, etc.
   *                   diagonal move--^   ^--residual x move
   */
  if( delta_y < delta_x ) {
    if( delta_y+delta_y < delta_x )
        nn= ((nn & 4) ? 7 : 1);
  }
  else
    if( delta_x+delta_x < delta_y )
        nn= ((nn & 2) ? 3 : 5);

  /*
   *  6 3 2   nn should now be one of these 8 possibilities.
   *  7 s 1   Translate (tx) it to your favourite DX ordering.
   *  4 5 0
   */
  return tx[nn];
}