proc b2d {b} {
    set sum 0;set len [string length $b]
    for {set i 0} {$i<$len} {incr i} {
        incr sum [expr int([string index $b $i]*pow(2,$len-$i-1))]
    }
    return $sum
}

proc d2b {d} {
    set b ""
    while {$d!=0} {
        set b "[expr $d%2]$b"
        set d [expr $d/2]
    }
    return $b
}

proc len2mask {len} {
    set mask ""
    for {set i 0} {$i<4} {incr i} {
        if {$len>=8} {
            lappend mask [b2d [formatb 8 8]]
            incr len -8
        } else {
            lappend mask [b2d [formatb $len 8]]
            set len 0
        }
    }
    return [join $mask .]
}

proc mask2len {mask} {
    set msks [split $mask .]
    set len 0
    for {set i 0} {$i<4} {incr i} {
        set m [lindex $msks $i]
        set str [d2b $m]
        incr len [string length [string trim $str 0]]
    }
    return $len
}