#!/bin/bash --
# Convert CIDR netmask to decimal x.x.x.x format and vice versa.

function cidr2oct () {
    local mask bit octs i
    mask=$1

    if grep -q '\.' <<<$mask; then
	echo $mask
	return
    fi

    for ((i=$mask; $i>0; i--)); do
	bit="${bit}1"
    done
    i=$((32 - $mask))
    for ((i=$i; $i>0; i--)); do
	bit="${bit}0"
    done

    octs=$(echo 'ibase=2;obase=A;'$(cut -c 1-8 <<<$bit) |bc)
    octs=${octs}.$(echo 'ibase=2;obase=A;'$(cut -c 9-16 <<<$bit) |bc)
    octs=${octs}.$(echo 'ibase=2;obase=A;'$(cut -c 17-24 <<<$bit) |bc)
    octs=${octs}.$(echo 'ibase=2;obase=A;'$(cut -c 25-32 <<<$bit) |bc)

    echo $octs
}

function oct2cidr () {
    local mask bit cidr i
    mask=$1

    if grep -qv '\.' <<<$mask; then
	echo $mask
	return
    fi

    for i in 1 2 3 4; do
	bit=${bit}$(printf "%08d" \
	    $(echo 'ibase=10;obase=2;'$(cut -d '.' -f $i <<<$mask) |bc))
    done
    cidr=$(echo -n ${bit%%0*} |wc -m)

    echo $cidr
}

mask=$1
if grep -q '\.' <<<$mask; then
    oct2cidr $mask
else
    cidr2oct $mask
fi