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https://issues.apache.org/jira/browse/ARROW-13769?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17405387#comment-17405387
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David Li commented on ARROW-13769:
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This would let us pre-compute the null count in if_else/case_when/coalesce and
friends? That would be useful.
> [C++] BitmapAnd, BitmapOr... could return the number of set bits
> ----------------------------------------------------------------
>
> Key: ARROW-13769
> URL: https://issues.apache.org/jira/browse/ARROW-13769
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Antoine Pitrou
> Priority: Minor
>
> When updating a validity bitmap using a bitwise operation such as AND or OR,
> it can be useful to also know the new validity count. It is probably costless
> to compute the new popcount inside BitmapAnd and friends. Micro-benchmarks
> will have to be run to validate that assumption.
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