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From "Dawid Weiss (JIRA)" <>
Subject [jira] [Commented] (LUCENE-3179) OpenBitSet.prevSetBit()
Date Tue, 07 Jun 2011 22:08:58 GMT


Dawid Weiss commented on LUCENE-3179:

I posted the benchmarks of intrinsic vs. manual (OpenBitSet) performance of nlz and pop (bitcount)
methods a while ago -- they should still be around JIRA somewhere. If I recall right, the
difference was significant, although not like an order of magnitude or  something... and on
CPUs without intrinsic instructions the implementation handcrafted by Yonik was actually faster
than the one in the standard library. Of course these days most CPUs will have popcnt/ nlz
instructions, so it makes sense to switch.

> OpenBitSet.prevSetBit()
> -----------------------
>                 Key: LUCENE-3179
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>            Reporter: Paul Elschot
>            Priority: Minor
>             Fix For: 3.3
>         Attachments: LUCENE-3179.patch
> Find a previous set bit in an OpenBitSet.
> Useful for parent testing in nested document query execution LUCENE-2454 .

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