On 5/8/2017 1:29 PM, Doug Lea wrote:
On 05/08/2017 02:14 PM, Isaac Levy wrote:
Original message below:
The JDK impl of bitCount can be improved -- though most users will get
the hotspot intrinsic. The best source I could find for the suggestion
below is page 195: http://support.amd.com/techdocs/25112.pdf
The int version differs from current implementation in that it uses
one multiply instead of two shift+adds. (Similarly for long.)
I wonder if there is any processor that does not already have a
bit-count instruction for which this is actually faster?
Some evidence either way would be helpful.
This is a case of "jmh results or it isn't faster." [1]
It is challenging to evaluate such changes as being universally faster
without benchmark results, especially for small methods like this.
Without compelling performance support, my preference would be to leave
the current Java implementation as-is, especially when there are VM
intrinsics on many platforms.
Thanks,
-Joe
[1] http://openjdk.java.net/projects/code-tools/jmh/
