Faster Math ?

[Andrew Haley]

On 09/11/17 15:02, Laurent Bourgès wrote:
> --- testing cbrt(double) = pow(double, 1/3) ---
> Loop on     Math.pow(double, 1/3), args in [-10.0,10.0], took 0.739 s
> Loop on FastMath.cbrt(double), args in [-10.0,10.0], took 0.166 s
> Loop on     Math.pow(double, 1/3), args in [-0.7,0.7], took 0.746 s
> Loop on FastMath.cbrt(double), args in [-0.7,0.7], took 0.166 s
> Loop on     Math.pow(double, 1/3), args in [-0.1,0.1], took 0.742 s
> Loop on FastMath.cbrt(double), args in [-0.1,0.1], took 0.165 s
> Loop on     Math.pow(double, 1/3), args in all magnitudes, took 0.753 s
> Loop on FastMath.cbrt(double), args in all magnitudes, took 0.244
> 
> Conclusion:
> - acos / asin / atan functions are quite slow: it confirms these are not
> optimized by hotspot intrinsics.
> 
> - cbrt() is slower than sqrt() : 1.1s vs 0.1 => 10x slower
> - cbrt() is slower than pow(1/3) : 1.1s vs 0.7s => 50% slower

No.  cbrt() is faster than pow(1/3) : 0.24 vs 0.75

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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