9prady9 commented on pull request #11674:
URL: https://github.com/apache/arrow/pull/11674#issuecomment-971576899


   > That said, I agree with @lidavidm : this may not be worth it. I 
experimented locally and it's not easy to do this without making performance 
suffer. My original intuition was that the CPU could easily parallelize 
popcounts with the load/stores and logical operations, but that seems to depend 
on compiler optimizations quite a bit.
   
   True, unless pop count on a byte is close to a noop (via some special 
instruction), popcount along with bitmap will incur additional cost.
   
   Having said that, since validity/null count on output is only provided on 
explicit user request, wouldn't it be nice to have the extra feature ? one less 
API call for user to get pop count on output. I assuming these functions are 
user facing(as they are exported), hence my comment.


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