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Floating Point to byte arrays re visited

Posted on 2006-10-23
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Last Modified: 2008-02-01
Ok. Recently some of you suggested how to convert a float number to a 4-byte array, and vice-versa.
and they worked well.

Now I am doing the same for 8-byte double numbers. I have writen the code and the class (some of the stuff is removed from this display).
Here is the class and the main() program. Can any experts in floating-point manipulation here tell why I am getting NaN when I ran this
example?

public class DoubleToByteArray
{
 public static byte[] toByteArray(double doubleVal)
   {
     byte[] dByteArray = new byte[8];
     long n = Double.doubleToLongBits(doubleVal);

     for(int i = 0;  i < dByteArray.length;  i++)
     {
        dByteArray[i] = (byte)(n >> (i * 8) &0xFF);  
     }
     
     return dByteArray;            
   }      
      
 
   public static double toDoubleValue(byte[] inBytes)
   {
     long n = 0;
     for(int i = 0;  i < inBytes.length;  i++)
     {
        n |= ((inBytes[i] & 0377) << (i * 8));
     }
     
     double doubleValue = Double.longBitsToDouble(n);

     return doubleValue;      
   }      
      
   public static void main(String [] args)
   {      
     double aValue = -46633.91;
     
     byte[] doubleBytes = ByteArray.toByteArray(aValue);
     
     double recreatedValue = ByteArray.toDoubleValue(doubleBytes);
     
     System.out.println("recreated : " + recreatedValue);
  }
}
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Question by:prain
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3 Comments
 
LVL 9

Accepted Solution

by:
shinobun earned 200 total points
ID: 17793262
((inBytes[i] & 0377) << (i * 8)) is being calculated as an int.  You need to cast it to a long:

 ((long) (inBytes[i] & 0377) << (i * 8));
0
 
LVL 14

Assisted Solution

by:hoomanv
hoomanv earned 100 total points
ID: 17794117
Just a recommendation, prevent excessive multiplication :)

// DoubleToByteArray
     for (int i = 0, shiftBy = 0; shiftBy < 64; shiftBy += 8) {
        dByteArray[i++] = (byte) (n >> shiftBy & 0xFF);  
     }

// toDoubleValue
     for (int i = 0, shiftBy = 0; shiftBy < 64; shiftBy += 8) {
        n |= (long) (inBytes[i++] & 0xFF) << shiftBy;
     }
0
 

Author Comment

by:prain
ID: 17795609
Thanks both of you. Hoomanv, thanks for the nice improved code.
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