shifting with negative numbers

[ram shah]

Pls explain the execution of the question given below....


code
--------------------------------------

public class Test{
public static void main(String args[]){
int a = -8;
int b = -33;
a>>>=b;
System.out.println(a);
}}
-----------------------------------------

How do we evaluate the problem when the shift distance is a negative number?

[chintan ramavat]

Right shift - number * 2^ whatever position (raise to)
Left shift - number / 2 ^ whatever position (raise to)

unsigned right shift - always positive

[chintan ramavat]

sorry my mistake - vice versa

[Henry Wong]

Previous discussion of this exact topic in this forum...

https://coderanch.com/t/263391/java-programmer-SCJP/certification/Shift-operators-negative-numbers

Henry

[ram shah]

henry,
in the rarlier discussion only the left hand operand was negative. here, both operands are negative. I've doubt regarding this situation only. How do we right shift or left shift a number(positive or negative) by a larger negative number?

[Henry Wong]

Originally posted by ram shah:
henry,
in the rarlier discussion only the left hand operand was negative. here, both operands are negative. I've doubt regarding this situation only. How do we right shift or left shift a number(positive or negative) by a larger negative number?

For shifting of ints only the lower 5 bits of right operand is significant (for longs, it is the lower 6 bits). Everything else from the previous discussion remains the same.

8 = 0000 0000 0000 0000 0000 0000 0000 1000
negate 8 = 1111 1111 1111 1111 1111 1111 1111 0111
twos comp 8 = 1111 1111 1111 1111 1111 1111 1111 1000 = -8

33 = 0000 0000 0000 0000 0000 0000 0010 0001
negate 33 = 1111 1111 1111 1111 1111 1111 1101 1110
twos comp 33 = 1111 1111 1111 1111 1111 1111 1101 1111 = -33
low 5 bits of -33 = 0000 0000 0000 0000 0000 0000 0001 1111 = 31

-8 = 1111 1111 1111 1111 1111 1111 1111 1000
-8 >>> 31 = 0000 0000 0000 0000 0000 0000 0000 0001 = 1

Henry

[ram shah]

Thanks Henry....I got it.