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UselesssCat
Asked: 2020-03-23 05:32:55 +0800 CST 2020-03-23 05:32:55 +0800 CST

How to reverse bytes of an integer in java?

  • 772

I have to go through a range of IPs, the problem is that the format that the function returns is inverted. The format returned by the function is:

First IP

108736
00000000 00000001 10101000 11000000
       0        1      168      192

Last IP

-16668480
11111111 00000001 10101000 11000000
     255        1      168      192

What I want is that they remain:

192.168.1.0      3232235776
192.168.1.255    3232236031

This to be able to go through them in a cycle.

Edit

The for is this:

for (int i = getNetworkIp(c) + 1, bc = getBroadCastIp(c); i < bc; i++) { 
    if (isReachable(intToIp(i))) { 
        ips += "ip " + intToIp(i) + " encontrada\n";
    }
}

The problem is that when doing the cycle I have left from: 108736 to -16668480

java

2 Answers

  1. What you want to do is convert the " endianess ".

    /* convierte de big-endian a little-endian y viceversa */
public static int convertEndianess(int i) {
    return (i & 0xff) << 24 | (i & 0xff00) << 8 | (i & 0xff0000) >> 8 | (i >> 24) & 0xff;
}

/* interpreta un int como unsigned, y lo devuelve como long */
public static long intToUnsignedAsLong(int x) {
    return ((long) x) & 0xFFFFFFFFL;
}

public static void main(String[] args) {
    int ip = 108736;
    int ip2 = convertEndianess(ip);
    System.out.println(intToUnsignedAsLong(ip2));
}

    This prints 3232235776 Note that normally the conversion to long(to see it as unsigned) is not necessary or desirable at all - if we omit that, the resulting number is-1062731520

    • 1
  2. Best Answer

    Can be used Integer.reverseBytes:

    int numBytesReversed = Integer.reverseBytes(num);

    There is also Integer.reversequereverses all bits of an int

    int numBitsReversed = Integer.reverse(num);
java.lang.Integer vínculos de API

public static int reverseBytes(int i)

    Returns the value obtained by reversing the order of the bytes in the two's complement representation of the specified int value.

    public static int reverse(int i)

    Returns the value obtained by reversing the order of the bits in the two's complement binary representation of the specified int value.

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