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https://issues.apache.org/jira/browse/MATH-579?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13034996#comment-13034996
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Luc Maisonobe commented on MATH-579:
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This is normal and is probably the same for all FastMath methods (I just
checked for sin, abs and sqrt, knowing that FastMath.sqrt simply calls
Math.sqrt). The initialization occurs at class loading as many tables are
computed, so this overhead occurs only one per program run and does not change
with the number of calls.
The number of calls is also important as the native code optimizing compilers
kicks of only after the same part of code has been used many times. FastMath
relies heavily on this and attempts to be fast for large scale computation. The
side effect you see is that it is much slower for very short programs like the
benchmark above.
Also note that 10 runs is far too low with regard to both the resolution of
currentTimeMillis (one can use System.nanoTime() instead) and for results
significance.
So I would like to close this as WONTFIX. Perhaps we should add in the javadoc
that FastMath targets large scale computation.
> FastMath.pow much slower than Math.pow
> --------------------------------------
>
> Key: MATH-579
> URL: https://issues.apache.org/jira/browse/MATH-579
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 3.0
> Environment: java version "1.6.0_22"
> OpenJDK Runtime Environment (IcedTea6 1.10.1) (6b22-1.10.1-0ubuntu1)
> OpenJDK 64-Bit Server VM (build 20.0-b11, mixed mode)
> java version "1.6.0_24"
> Java(TM) SE Runtime Environment (build 1.6.0_24-b07)
> Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02, mixed mode)
> Reporter: Arne Plöse
>
> calculating FastMath.pow(10, 0.1 / 20) is approximately 65 times slower as
> the Math.pow() function.
> Ether this is a bug or a javadoc comment is missing.
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