Re: BigInteger Class

From:
Razii <DONTwhatevere3e@hotmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Fri, 21 Mar 2008 05:12:36 -0500
Message-ID:
<8pv6u39vat02p9aot0dfarekrlu0gr2fhk@4ax.com>
On Fri, 21 Mar 2008 07:29:33 GMT, Roedy Green
<see_website@mindprod.com.invalid> wrote:

The problem is the internal form and external human-readable form are
quite different and it takes quite a bit of computation to
interconvert them. Your only hope is to find some representation that
takes less effort to export, e.g. hex.

Another approach is to get a HEX editor and look at a binary dump of
the file recorded in some internal binary format the way we used to in
the olden days.


Ok... have a look at this version. It doesn't work exactly (especially
if you increase the length of the BigInteger. I am not sure where
exactly the problem is. If you can fix it, post the version

import java.io.*;
import java.math.*;
import java.util.*;

public class BigNumber {
        
    public static void main(String[] args) throws Exception
   {
      FileWriter fstream = new FileWriter("number.txt");
      BufferedWriter fout = new BufferedWriter(fstream);
      PrintWriter out = new PrintWriter (fout);
           
       BigInteger bigInteger = new BigInteger (30,new Random());
       
       System.out.println(bigInteger);

       byte[] byteArray = bigInteger.toByteArray();
       int[] intArray = byteArrayToIntArray(byteArray, byteArray[0] <
0 ? -1 : 0);
       
       for (int i : intArray)
       {
        System.out.println(i);
        out.print(i);
       }
       out.flush();
    }
    
/** Convert a big-endian byte array to a little-endian array of words.
*/
    private static int[] byteArrayToIntArray(byte[] bytes, int sign)
   {
       // Determine number of words needed.
       int[] words = new int[bytes.length/4 + 1];
       int nwords = words.length;
  
      // Create a int out of modulo 4 high order bytes.
      int bptr = 0;
      int word = sign;
     for (int i = bytes.length % 4; i > 0; --i, bptr++)
      word = (word << 8) | (bytes[bptr] & 0xff);
     words[--nwords] = word;

     // Elements remaining in byte[] are a multiple of 4.
      while (nwords > 0)
       words[--nwords] = bytes[bptr++] << 24 |
              (bytes[bptr++] & 0xff) << 16 |
            (bytes[bptr++] & 0xff) << 8 |
            (bytes[bptr++] & 0xff);
     return words;
   }

    
}

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