def valid_ip?(cm, ip)
      size = cm.lines.size
      ip >= 0 && ip < cm.lines[size-1]
    end
def valid_ip?(cm, ip)
      size = cm.lines.size
      ip >= 0 && ip < cm.lines[size-1]
    end
Return true if ip is the start of some instruction in meth.
 FIXME: be more stringent.