Shift Operators

[Mubeen Shaik]

Hi All,

This code is from Marcus Green (Tutorial 5th Chapter).Output for this is 0 and 3.My question is how 3 >> 32 will give output 3?.

My Explanation
====================================
Values 32 is greater than 8. So it will do the moduls with 8 (32 % 8), result is 0. So it will not do any shift operation.

Is this correct?.

I am confused because it is showing 32%32. What is this ?.

=====================================

  
 
public class shift{
 
   public static void main(String argv[]){ 
        System.out.println(32 % 32);
        System.out.println( 3  >>> 32); 
        } 
 }
 

Thanks in advance,
Mubeen.

[Steve Morrow]

When you right shift by int n, Java only considers the five lowest bits (i.e., n & 0x1F). If n == 32, then n & 0x1F == 0, so you see effectively no shift.

Shifts with long values consider the six lowest bits; i.e., n & 0x3F.

Hope this helps.


P.S. Take a look at the following:

Cat and Mouse Games with Bits
Java Tutorial: Shift and Logical Operators
[ February 17, 2005: Message edited by: Steve Morrow ]

[Mubeen Shaik]

Steve,

I didn't get this.

=============================================================


Java only considers the five lowest bits (i.e., n & 0x1F).

=============================================================

Please explain.

Thanks,
Mubeen.

[Jeff Bosch]

From the Java Language Specification:

15.18 Shift Operators

The shift operators include left shift <<, signed right shift >>, and unsigned right shift >>>; they are syntactically left-associative (they group left-to-right). The left- hand operand of a shift operator is the value to be shifted; the right-hand operand specifies the shift distance.

ShiftExpression:
AdditiveExpression
ShiftExpression << AdditiveExpression
ShiftExpression >> AdditiveExpression
ShiftExpression >>> AdditiveExpression

The type of each of the operands of a shift operator must be a primitive integral type, or a compile-time error occurs. Binary numeric promotion (�5.6.2) is not performed on the operands; rather, unary numeric promotion (�5.6.1) is performed on each operand separately. The type of the shift expression is the promoted type of the left-hand operand.
If the promoted type of the left-hand operand is int, only the five lowest-order bits of the right-hand operand are used as the shift distance. It is as if the right-hand operand were subjected to a bitwise logical AND operator & (�15.21.1) with the mask value 0x1f. The shift distance actually used is therefore always in the range 0 to 31, inclusive.

If the promoted type of the left-hand operand is long, then only the six lowest-order bits of the right-hand operand are used as the shift distance. It is as if the right-hand operand were subjected to a bitwise logical AND operator & (�15.21.1) with the mask value 0x3f. The shift distance actually used is therefore always in the range 0 to 63, inclusive.

So, if your AdditiveExpression = 32, then 32 in binary is 0010 0000. AND that with 1F (0001 1111) and you get 0, so the value is not shifted at all.