1. IP Address to Decimal
We show you two ways to convert an IP address to a decimal number
- Normal power of 256
- Bit shifting
1.1 First Example – Power of 256
The IP address is “base 256″, to convert 192.168.1.2 to decimal (base 10) the formula is:
192 x (256)^3 + 168 x (256)^2 + 1 x (256)^1 + 2 (256)^0 = ? 3221225472 + 11010048 + 256 + 2 = 3232235778
public long ipToLong(String ipAddress) {
String[] ipAddressInArray = ipAddress.split("\\.");
long result = 0;
for (int i = 0; i < ipAddressInArray.length; i++) {
int power = 3 - i;
int ip = Integer.parseInt(ipAddressInArray[i]);
result += ip * Math.pow(256, power);
}
return result;
}
Some developers prefer to use modular like this
result += (Integer.parseInt(ipAddressInArray[i]) % 256 * Math.pow(256, power));
1.2 Second Example – Bit shifting
Review the binary bit shifting graph below :
public long ipToLong(String ipAddress) {
long result = 0;
String[] ipAddressInArray = ipAddress.split("\\.");
for (int i = 3; i >= 0; i--) {
long ip = Long.parseLong(ipAddressInArray[3 - i]);
//left shifting 24,16,8,0 and bitwise OR
//1. 192 << 24
//1. 168 << 16
//1. 1 << 8
//1. 2 << 0
result |= ip << (i * 8);
}
return result;
}
192 00000000 00000000 00000000 11000000 ----------------------------------------------- 192 << 24 11000000 00000000 00000000 00000000 Result 00000000 00000000 00000000 00000000 Result |= 11000000 00000000 00000000 00000000 168 00000000 00000000 00000000 10101000 ----------------------------------------------- 168 << 16 00000000 10101000 00000000 00000000 Result 11000000 00000000 00000000 00000000 Result |= 11000000 10101000 00000000 00000000 1 00000000 00000000 00000000 00000001 ----------------------------------------------- 1 << 8 00000000 00000000 00000001 00000000 Result 11000000 10101000 00000000 00000000 Result |= 11000000 10101000 00000001 00000000 2 00000000 00000000 00000000 00000010 ----------------------------------------------- 2 << 0 00000000 00000000 00000000 00000010 Result 11000000 10101000 00000001 00000000 Result |= 11000000 10101000 00000001 00000010
Convert the final binary code to decimal, by hand calculation :) ~
Result 11000000 10101000 00000001 00000010
index 0 - 31, start from right.
31(1),30(1),29,28,27,26,25,24,23(1),22,21(1),20,19(1),18,17,16,15,14,13,12,11,10,9,8(1),7,6,5,4,3,2,1(1),0
Decimal 1x2^31 + 1x2^30 + 1x2^23 + 1x2^21 + 1x2^19 + 1x2^8 + 1x2^1
2147483648 + 1073741824 + 8388608 + 2097152 + 524288 + 256 + 2
3232235778
2. Decimal to IP Address
We show you two bit shifting and “0xff” masking examples to convert a decimal number back to IP address. The bit shifting is very hard to explain in words, it’s better review the binary flows below :
2.1 First Example.
//ip = 3232235778
public String longToIp(long ip) {
StringBuilder result = new StringBuilder(15);
for (int i = 0; i < 4; i++) {
result.insert(0,Long.toString(ip & 0xff));
if (i < 3) {
sb.insert(0,'.');
}
ip = ip >> 8;
}
return result.toString();
}
Review the bit shifting flows :
3232235778 11000000 10101000 00000001 00000010 <<Loop 1>> ----------------------------------------------------------- ip 11000000 10101000 00000001 00000010 & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 00000010 = 2 Result Append .2 -------------------------> 8 ip >> 8 00000000 11000000 10101000 00000001 {off 00000010} <<Loop 2>> ----------------------------------------------------------- ip 00000000 11000000 10101000 00000001 & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 00000001 = 1 Result Append 1.2 ----------------> 8 ip >> 8 00000000 00000000 11000000 10101000 {off 00000001} <<Loop 3>> ----------------------------------------------------------- ip 00000000 00000000 11000000 10101000 & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 10101000 = 168 Result Append 168.1.2 -------> 8 ip >> 8 00000000 00000000 00000000 11000000 {off 10101000} <<Loop 4>> ----------------------------------------------------------- ip 00000000 00000000 00000000 11000000 & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 11000000 = 192 Result Append 192.168.1.2 -----------> 8 ip >> 8 00000000 00000000 00000000 00000000 {off 11000000}
2.2 Second Example.
//ip = 3232235778
public String longToIp(long ip) {
return ((ip >> 24) & 0xFF) + "."
+ ((ip >> 16) & 0xFF) + "."
+ ((ip >> 8) & 0xFF) + "."
+ (ip & 0xFF);
}
3232235778 11000000 10101000 00000001 00000010 1. (ip >> 24) & 0xFF ----------------------------------------------------------- ip 11000000 10101000 00000001 00000010 -------------------------------------> 24 ip >> 24 00000000 00000000 00000000 11000000 {off 10101000 00000001 00000010} & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 11000000 = 192 2. (ip >> 16) & 0xFF ----------------------------------------------------------- ip 11000000 10101000 00000001 00000010 -------------------------------------> 16 ip >> 16 00000000 00000000 11000000 10101000 {off 00000001 00000010} & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 10101000 = 168 3. (ip >> 8) & 0xFF ----------------------------------------------------------- ip 11000000 10101000 00000001 00000010 --------------------------------------> 8 ip >> 24 00000000 11000000 10101000 00000001 {off 00000010} & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 00000001 = 1 4. ip & 0xFF ----------------------------------------------------------- ip 11000000 10101000 00000001 00000010 & 0xff 00000000 00000000 00000000 11111111 Result 00000000 00000000 00000000 00000010 = 2
3. Java Source Code
Full Java example to demonstrate above scenario :
package com.mkyong.core;
public class JavaBitwiseExample {
public static void main(String[] args) {
JavaBitwiseExample obj = new JavaBitwiseExample();
System.out.println("iptoLong : " + obj.ipToLong("192.168.1.2"));
System.out.println("iptoLong2 : " + obj.ipToLong2("192.168.1.2"));
System.out.println("longToIp : " + obj.longToIp(3232235778L));
System.out.println("longToIp2 : " + obj.longToIp2(3232235778L));
}
// example : 192.168.1.2
public long ipToLong(String ipAddress) {
// ipAddressInArray[0] = 192
String[] ipAddressInArray = ipAddress.split("\\.");
long result = 0;
for (int i = 0; i < ipAddressInArray.length; i++) {
int power = 3 - i;
int ip = Integer.parseInt(ipAddressInArray[i]);
// 1. 192 * 256^3
// 2. 168 * 256^2
// 3. 1 * 256^1
// 4. 2 * 256^0
result += ip * Math.pow(256, power);
}
return result;
}
public long ipToLong2(String ipAddress) {
long result = 0;
String[] ipAddressInArray = ipAddress.split("\\.");
for (int i = 3; i >= 0; i--) {
long ip = Long.parseLong(ipAddressInArray[3 - i]);
// left shifting 24,16,8,0 and bitwise OR
// 1. 192 << 24
// 1. 168 << 16
// 1. 1 << 8
// 1. 2 << 0
result |= ip << (i * 8);
}
return result;
}
public String longToIp(long i) {
return ((i >> 24) & 0xFF) +
"." + ((i >> 16) & 0xFF) +
"." + ((i >> 8) & 0xFF) +
"." + (i & 0xFF);
}
public String longToIp2(long ip) {
StringBuilder sb = new StringBuilder(15);
for (int i = 0; i < 4; i++) {
// 1. 2
// 2. 1
// 3. 168
// 4. 192
sb.insert(0, Long.toString(ip & 0xff));
if (i < 3) {
sb.insert(0, '.');
}
// 1. 192.168.1.2
// 2. 192.168.1
// 3. 192.168
// 4. 192
ip = ip >> 8;
}
return sb.toString();
}
/*
private static void printPrettyBinary(String binary) {
String s1 = String.format("%32s", binary).replace(' ', '0');
System.out.format("%8s %8s %8s %8s %n",
s1.substring(0, 8),
s1.substring(8, 16),
s1.substring(16, 24),
s1.substring(24, 32));
}
*/
}
Output
iptoLong : 3232235778 iptoLong2 : 3232235778 longToIp : 192.168.1.2 longToIp2 : 192.168.1.2