regarding Shift Operators

[Krishna Bulusu]

hi,
i couldn't understand the Shift operator("<<",">>",">>>") mechanism....
can any one plz explin this.....

thanks in Advance
regards
krishna.

[Flom Xanther]

First I was afraid too...I also couldn't understand the whole shifting thing..

But its sooo easy once you try and code something..
Maybe you can specify your question?!

First of all, you can only shift integral values (int,long)
(You can shift narrower types too, but the operation is always at least performed on int)

right shift (>> ) shifts the bit-representation of the value to the right and fills the resulting "empty space" on the left side with the value of the most significant bit before the shift (the leftmost), so it's a "signed shift", cause if the leftmost bit was 1 (negative) before the shift, it will be negative after the shift..(value is divided by 2 on a shift by 1)

left shift(<< ) shifts to left, and the right side will be filled with zeros(0)..(value is multiplied by 2 on a shift by 1)

unsigned right shift (>>> ) shifts to right, but always fills the space with zeros..

But maybe you dont understand the whole binary 1 and 0 thing?

Regards,
Flom

[ May 26, 2006: Message edited by: Flom Xanther ]
[ May 26, 2006: Message edited by: Flom Xanther ]

[wise owen]

int n = 0xffffffff;
 
System.out.println("n = " + Integer.toHexString(n) + " with >>");
System.out.println("(n>>5) = " + Integer.toHexString(n>>5));
System.out.println("(n>>31) = " + Integer.toHexString(n>>31));
System.out.println("(n>>32) = " + Integer.toHexString(n>>32));
 
n = 0xffffffff;
System.out.println("n = " + Integer.toHexString(n) + " with <<");
System.out.println("(n<<5) = " + Integer.toHexString(n<<5));
System.out.println("(n<<31) = " + Integer.toHexString(n<<31));
System.out.println("(n<<32) = " + Integer.toHexString(n<<32));

n = 0xffffffff;
System.out.println("n = " + Integer.toHexString(n) + " with >>>");
System.out.println("(n>>>5) = " + Integer.toHexString(n>>>5));
System.out.println("(n>>>31) = " + Integer.toHexString(n>>>31));
System.out.println("(n>>>32) = " + Integer.toHexString(n>>>32));
System.out.println("(n>>>33) = " + Integer.toHexString(n>>>33)); //33-32

int p = 0x7fffffff;
 
System.out.println("p = " + Integer.toHexString(p) + " with >>");
System.out.println("(p>>5) = " + Integer.toHexString(p>>5));
System.out.println("(p>>31) = " + Integer.toHexString(p>>31));
System.out.println("(p>>32) = " + Integer.toHexString(p>>32));
 
p = 0x7fffffff;
System.out.println("p = " + Integer.toHexString(p) + " with <<");
System.out.println("(p<<5) = " + Integer.toHexString(p<<5));
System.out.println("(p<<31) = " + Integer.toHexString(p<<31));
System.out.println("(p<<32) = " + Integer.toHexString(p<<32));

p = 0x7fffffff;
System.out.println("p = " + Integer.toHexString(p) + " with >>>");
System.out.println("(p>>>5) = " + Integer.toHexString(p>>>5));
System.out.println("(p>>>31) = " + Integer.toHexString(p>>>31));
System.out.println("(p>>>32) = " + Integer.toHexString(p>>>32));
System.out.println("(p>>>33) = " + Integer.toHexString(p>>>33)); 

Get some feeling from code. The output

 
n = ffffffff with >>
(n>>5) = ffffffff
(n>>31) = ffffffff
(n>>32) = ffffffff
n = ffffffff with <<
(n<<5) = ffffffe0
(n<<31) = 80000000
(n<<32) = ffffffff
n = ffffffff with >>>
(n>>>5) = 7ffffff
(n>>>31) = 1
(n>>>32) = ffffffff
(n>>>33) = 7fffffff
p = 7fffffff with >>
(p>>5) = 3ffffff
(p>>31) = 0
(p>>32) = 7fffffff
p = 7fffffff with <<
(p<<5) = ffffffe0
(p<<31) = 80000000
(p<<32) = 7fffffff
p = 7fffffff with >>>
(p>>>5) = 3ffffff
(p>>>31) = 0
(p>>>32) = 7fffffff
(p>>>33) = 3fffffff

[Krishna Bulusu]

thank u very much flom...

i got one shortcut for "<<"..
let us say int i=4;
inr result=i<<4 is nothing but 4*2 power 4 ie, 4*16=64.

is it true??

regards,
krishna

[wise owen]

You are right:

let us say int i=4;
int result=i<<4 is nothing but 4*2 power 4 ie, 4*16=64.

But, you need to consider how many bits for one "int":

    
int i =4;
int result;
result = i<<29; //is -2147483648
result = i<<30; //is 0
result = i<<31; //is 0
result = i<<32; //is 4
result = i<<33; //is 8