Using boolean expression Bash script

Hi,
Im trying to write a Bash script that calculates the least common subnet for two address.

Theoretical: I have to change IP from decimal to binary, then apply XNOR on the two IPs.

I tried to write this:

#!/bin/bash
echo "Ebter the first ip"
read ip1
echo "Enter the second ip"
read ip2 

#Separate octs of first ip  

a1=`echo $ip1 | awk 'BEGIN{FS="."}{print $1}'`
a2=`echo $ip1 | awk 'BEGIN{FS="."}{print $2}'`
a3=`echo $ip1 | awk 'BEGIN{FS="."}{print $3}'`
a4=`echo $ip1 | awk 'BEGIN{FS="."}{print $4}'`  
#convert decimal to binary

b1=`echo "obase=2;$a1" | bc`
b2=`echo "obase=2;$a2" | bc`
b3=`echo "obase=2;$a3" | bc`
b4=`echo "obase=2;$a4" | bc`  

#Separate octs of second ip

c1=`echo $ip2 | awk 'BEGIN{FS="."}{print $1}'`
c2=`echo $ip2 | awk 'BEGIN{FS="."}{print $2}'`
c3=`echo $ip2 | awk 'BEGIN{FS="."}{print $3}'`
c4=`echo $ip2 | awk 'BEGIN{FS="."}{print $4}'`  

#convert decimal to binary (second IP)

d1=`echo "obase=2;$c1" | bc`
d2=`echo "obase=2;$c2" | bc`
d3=`echo "obase=2;$c3" | bc`
d4=`echo "obase=2;$c4" | bc`

e1=`echo $b1 || $d1 | rev`
e2=`echo $b2 || $d2 | rev`
e3=`echo $b3 || $d3 | rev`
e4=`echo $b4 || $d4 | rev`

echo "$e1.$e2.$e3.$e4"    

I have two problems:

I need to apply XNOR to the binary IP (bit by bit), but if the result of a specific bit becomes zero I want to stop the operation and make another bit that follows the zero, zero also.

I need that XNOR ignores "."

Can someone help me with this issue please?

Can't you apply/modify the priciples of this post?

Im new begining in Bash script, so your script is hard for me to understand.
couldnt you help me with my simple script

I'd love to - if I only understood what you're after.
The mentioned scriptlet creates a 32-bit binary equivalent of an IP4 address and then XORs it with another. So - analyzing and testing it line by line could help you do what you need.

First i converted both deimal ip to binary.
i need to make a for loop that will compare the binary bits (bit by bit) (using XNOR) of first and second ip

XNOR theory:
1- if the bits of first and second ip equal, result will be 1
2- if they are diferent the result will be 0

But if the result become 0 of any two bits, the comparisation will stop and put 0 to the another bits without compare them

How about this:

#!/bin/bash
dec2bin () {
  # dec2bin num [width] [var]
  local bin=""
  for((num=$1;num;num/=2))
  do
    bin=$((num%2))$bin
  done
  ((${#3})) &&
      printf -v ${3} "%0*d" ${2:-1} $bin ||
      printf "%0*d" ${2:-1} $bin
}

xnor () {
    # xnor bits1 bits2 [var]
    local res=""
    for((bit=0;bit<${#1};bit++))
    do
        if ((!done&&${1:bit:1}==${2:bit:1}))
        then
          res=${res}1
        else
          done=1
          res=${res}0
        fi
    done
    ((${#3})) &&
      printf -v ${3} "%d" $((2#$res)) ||
      printf "%d" $((2#$res))
}

echo "Enter the first ip"
read ip1
echo "Enter the second ip"
read ip2

#Separate octs of first ip
set ${ip1//./ }

#convert decimal to binary
dec2bin $1 8 a1
dec2bin $2 8 a2
dec2bin $3 8 a3
dec2bin $4 8 a4

#Separate octs of second ip
set ${ip2//./ }

#convert decimal to binary (second IP)
dec2bin $1 8 b1
dec2bin $2 8 b2
dec2bin $3 8 b3
dec2bin $4 8 b4

done=0
xnor $a1 $b1 c1
xnor $a2 $b2 c2
xnor $a3 $b3 c3
xnor $a4 $b4 c4

echo $c1.$c2.$c3.$c4

Result:

Enter the first ip
192.168.16.55
Enter the second ip
192.168.7.55
255.255.224.0

Thanks Chubler_XL for ur answer

Ooohh - you're after the netmask. Try

{ read IP1; read IP2; } < file1
BIP1=$(( 0x$(printf "%02X" ${IP1//./ })))
BIP2=$(( 0x$(printf "%02X" ${IP2//./ })))
TMP=$(( BIP1 ^ BIP2 ))
I=1
while [ $(( I*=2 )) -lt $TMP ]; do :; done                           
I=$(( --I ^ 2**32-1 ))
printf "%d.%d.%d.%d\n" $((I>>24)) $((I>>16&255)) $((I>>8&255)) $((I&255))
255.255.224.0

---------- Post updated at 14:30 ---------- Previous update was at 14:13 ----------

or

{ read IP1; read IP2; } < file1
BIP1=$(( 0x$(printf "%02X" ${IP1//./ })))
BIP2=$(( 0x$(printf "%02X" ${IP2//./ })))
TMP=$(( BIP1 ^ BIP2 ))   
while (( TMP )); do TMP=$((TMP>>1)); ((I++)); done
I=$((2**32-1 ^ 2**I-1))
printf "%d.%d.%d.%d\n" $((I>>24)) $((I>>16&255)) $((I>>8&255)) $((I&255))