Re: Long integer to bytes?

nooneinparticular314159@yahoo.com wrote:


Just use a DataOutputStream.

The unsigned arithmetic can be performed using longs. When you are ready to
output the data you mask the low order 4 bytes into an int. Then write the int
directly to the network using DataOutputStream.writeInt(). Java I/O is all
network byte order (big endian) so there's no need to worry about byte
swapping.

The following code will write the unsigned value 0xfedcba01 to a file:

package tests;

import java.io.DataOutputStream;
import java.io.FileOutputStream;

public class IntOutput {
    public static void main(String[] args) {
        // create a 32bit, "unsigned" integer.
        long l = 0xfedcba01L;
        
        // mask off the 32bit low order bits into an int.
        int i = (int) l & 0xffffffff;
        System.out.println(l);
        System.out.println(i);
        
        try {
            // open a DataOutputStream, in this case to a file, but it could
            // just as easily be network connection.
            FileOutputStream fos = new FileOutputStream("tmp.tmp");
            DataOutputStream dos = new DataOutputStream(fos);
            
            dos.writeInt(i);
            
            dos.close();
            fos.close();
        }
        catch(Exception e) {
            System.err.println(e);
        }
    }
}

When you run it the output is:
4275878401
-19088895

The contents of the output file, when viewed using od are:

$ od -t x4 tmp.tmp
0000000 fedcba01 HEX
$ od -D tmp.tmp
0000000 4275878401 Unsigned int
$ od -t d4 tmp.tmp
0000000 -0019088895 Signed int

--
Nigel Wade, System Administrator, Space Plasma Physics Group,
            University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555