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Posted to dev@lucene.apache.org by Dawid Weiss <da...@cs.put.poznan.pl> on 2014/11/07 08:41:20 UTC
Re: Processor support for select operations?
Hi Paul,
I think compiler-dev hotspot list would be adequate. Coincidentally,
John Rose mentioned ffs (find first bit set) ops just recently and
gave an interesting link to all sorts of implementations:
http://markmail.org/message/siucbahtw2jzblzl
Dawid
On Thu, Nov 6, 2014 at 5:18 PM, Paul Elschot <pa...@gmail.com> wrote:
> Dear all,
>
> For LUCENE-6040 it would be good to have better processor support for
> selecting the i-th set bit from a 64-bit integer.
>
> Not too long ago Long.bitCount() was intrinsified in JVM's.
>
> I hope something similar will happen to a select(long x, int i)
> method. However, better processor support is needed first.
>
> This is somewhat off topic here, but does anyone know how to request
> better processor support for select operations?
>
>
> Regards,
> Paul Elschot
>
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Re: Processor support for select operations?
Posted by Dawid Weiss <da...@cs.put.poznan.pl>.
And here's a very recent (still active, in fact) thread on how to add
a new intrinsic instruction to hotspot :)
http://markmail.org/message/xosi5azzc3hknab7
D.
On Fri, Nov 7, 2014 at 8:46 AM, Dawid Weiss
<da...@cs.put.poznan.pl> wrote:
> And there's always hacker's delight if you're sure popcnt is efficient:
>
> ctz(x) = pop((x & (−x)) − 1)
> ffs(x) = pop(x ^ (~(−x)))
>
> D.
>
> On Fri, Nov 7, 2014 at 8:41 AM, Dawid Weiss
> <da...@cs.put.poznan.pl> wrote:
>> Hi Paul,
>>
>> I think compiler-dev hotspot list would be adequate. Coincidentally,
>> John Rose mentioned ffs (find first bit set) ops just recently and
>> gave an interesting link to all sorts of implementations:
>>
>> http://markmail.org/message/siucbahtw2jzblzl
>>
>> Dawid
>>
>> On Thu, Nov 6, 2014 at 5:18 PM, Paul Elschot <pa...@gmail.com> wrote:
>>> Dear all,
>>>
>>> For LUCENE-6040 it would be good to have better processor support for
>>> selecting the i-th set bit from a 64-bit integer.
>>>
>>> Not too long ago Long.bitCount() was intrinsified in JVM's.
>>>
>>> I hope something similar will happen to a select(long x, int i)
>>> method. However, better processor support is needed first.
>>>
>>> This is somewhat off topic here, but does anyone know how to request
>>> better processor support for select operations?
>>>
>>>
>>> Regards,
>>> Paul Elschot
>>>
>>> ---------------------------------------------------------------------
>>> To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
>>> For additional commands, e-mail: dev-help@lucene.apache.org
>>>
---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
For additional commands, e-mail: dev-help@lucene.apache.org
Re: Processor support for select operations?
Posted by Dawid Weiss <da...@cs.put.poznan.pl>.
And there's always hacker's delight if you're sure popcnt is efficient:
ctz(x) = pop((x & (−x)) − 1)
ffs(x) = pop(x ^ (~(−x)))
D.
On Fri, Nov 7, 2014 at 8:41 AM, Dawid Weiss
<da...@cs.put.poznan.pl> wrote:
> Hi Paul,
>
> I think compiler-dev hotspot list would be adequate. Coincidentally,
> John Rose mentioned ffs (find first bit set) ops just recently and
> gave an interesting link to all sorts of implementations:
>
> http://markmail.org/message/siucbahtw2jzblzl
>
> Dawid
>
> On Thu, Nov 6, 2014 at 5:18 PM, Paul Elschot <pa...@gmail.com> wrote:
>> Dear all,
>>
>> For LUCENE-6040 it would be good to have better processor support for
>> selecting the i-th set bit from a 64-bit integer.
>>
>> Not too long ago Long.bitCount() was intrinsified in JVM's.
>>
>> I hope something similar will happen to a select(long x, int i)
>> method. However, better processor support is needed first.
>>
>> This is somewhat off topic here, but does anyone know how to request
>> better processor support for select operations?
>>
>>
>> Regards,
>> Paul Elschot
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
>> For additional commands, e-mail: dev-help@lucene.apache.org
>>
---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
For additional commands, e-mail: dev-help@lucene.apache.org