Bitwise rotation

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Carles Company Soler - 09 Mar 2005 09:52 GMT

Hello,
does java have a bitwise rotation operator for Integers?

Thanks!

Carles

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Daniel Tryba - 09 Mar 2005 11:14 GMT

> does java have a bitwise rotation operator for Integers?

Yes.
http://java.sun.com/docs/books/tutorial/java/nutsandbolts/bitwise.html

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Eric Sosman - 09 Mar 2005 15:35 GMT

>>does java have a bitwise rotation operator for Integers?

^^^^^^^^ ^^^^^^^^

> Yes.

No.

To rotate (not merely shift) an int (not an Integer)
you need an expression something like

(i << n) | (i >>> (32 - n))

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Daniel Tryba - 10 Mar 2005 00:19 GMT

>>>does java have a bitwise rotation operator for Integers?
> ^^^^^^^^ ^^^^^^^^
[quoted text clipped - 7 lines]
>
> (i << n) | (i >>> (32 - n))

I stand correced, mis interpreted due to out of coffee error :)

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Daniel Sjöblom - 11 Mar 2005 15:45 GMT

>>>does java have a bitwise rotation operator for Integers?
>
[quoted text clipped - 4 lines]
>
> (i << n) | (i >>> (32 - n))

Not true in java 1.5, since there are ror/rol operations in
java.lang.Math or Integer, I can't recall which right now. Of course,
they are fairly disappointing (from a performance point of view) since
they are just wrappers that do just the above, although I suspect they
will be compiler intrinsics in later VM versions.

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Thomas G. Marshall - 14 Mar 2005 15:38 GMT

Eric Sosman coughed up:

>>> does java have a bitwise rotation operator for Integers?
> ^^^^^^^^ ^^^^^^^^
[quoted text clipped - 7 lines]
>
> (i << n) | (i >>> (32 - n))

For some reason, this ROR seems much more readable to me:

(i << (32-n)) | (i >>> n)

I think because it deals with the left most bit first, and I think left to
right. "Left" is highbit, because of the way you write down binary on
paper.

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Eric Sosman - 14 Mar 2005 17:19 GMT

> Eric Sosman coughed up:
>
[quoted text clipped - 18 lines]
> right. "Left" is highbit, because of the way you write down binary on
> paper.

That's one of the reasons I wrote "something like" ;-)
My mental picture of a rotation is "shift, then replace the
bits that fell off the end." De gustibus non disputandum est.

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Bitwise rotation

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