proc between {a b x} {return [expr {$x<=$b && $x>=$a}]}

proc address {num} {
  if {[between 10 249 $num]} {return 192.168.209.$num}
  if {[between 250 489 $num]} {return 192.168.109.[expr {$num-240}]}
  if {[between 510 778 $num]} {return 192.168.9.[expr {$num-500}]}
}

address 188
address 310
address 533