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https://issues.apache.org/jira/browse/MATH-650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13099632#comment-13099632
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Gilles commented on MATH-650:
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IIUC, only the initializations needed by a method call are performed.
Thus "max" has become fast because it doesn't need any of those data arrays.
For those methods that need the data, one has to compare the startup times
between computing the data and loading precomputed data. For methods that only
need some of the data, the time gain might not be worth trailing the huge
precomputed arrays.
If several calls are made to methods that need most of the data arrays, the
initialization time will be increasingly negligible (with respect to the
"useful" application running time). Which again renders the precomputed arrays
unnecessary.
So, in summary, lazy initialization is very nice, especially for short-lived
applications that happen to call methods that don't need the data at all.
It's still nice for applications that happen to need only part of the data.
It's useless for applications that will need all the data arrays. (But it
probably does not hurt.)
However, I still don't see an advantage in storing precomputed values. I don't
think that it should be adopted just for a toy application that would call a
math function once and exit.
> FastMath has static code which slows the first access to FastMath
> -----------------------------------------------------------------
>
> Key: MATH-650
> URL: https://issues.apache.org/jira/browse/MATH-650
> Project: Commons Math
> Issue Type: Improvement
> Affects Versions: Nightly Builds
> Environment: Android 2.3 (Dalvik VM with JIT)
> Reporter: Alexis Robert
> Priority: Minor
>
> Working on an Android application using Orekit, I've discovered that a simple
> FastMath.floor() takes about 4 to 5 secs on a 1GHz Nexus One phone (only the
> first time it's called). I've launched the Android profiling tool (traceview)
> and the problem seems to be linked with the static portion of FastMath code
> named "// Initialize tables"
> The timing resulted in :
> - FastMath.slowexp (40.8%)
> - FastMath.expint (39.2%)
> \- FastMath.quadmult() (95.6% of expint)
> - FastMath.slowlog (18.2%)
> Hoping that would help
> Thanks!
> Alexis Robert
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