FRF: 8033792: AltHashing used jint for imprecise bit shifting

[David Holmes]

Hi Yumin,

On 7/02/2014 2:14 PM, Yumin Qi wrote:
> Hi,
>
>    Please review the change for 8033792.
>
>    Summary:  AltHashing uses 'jint' type in the way as 'unsigned int' in
> bit shifting, which is imprecise.  This could lead loss of precision
> when converted between jint and 'unsigned int' during bit operation. Fix
> by changing operation variable type from 'jint' to 'juint', before
> return, cast it into type 'jint'.
>
> http://cr.openjdk.java.net/~minqi/8033792/webrev00/

I don't see how casting to unsigned int can lead to a loss of precision 
here. Further you now assign h1 from a jint and you pass it as a jint 
parameter to the Integer_rotate functions which would seem to me to have 
more opportunity for conversion issues. Either way this code is 
completely confused about the type of arithmetic it is trying to do (and 
I would think a hash should be unsigned to begin with ??).

You didn't mention the unrelated change in 
src/share/vm/oops/instanceKlass.hpp

Thanks,
David

> Thanks
> Yumin