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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-650) FastMath has static code which slows the first access to FastMath
Date Wed, 21 Sep 2011 15:07:09 GMT

    [ https://issues.apache.org/jira/browse/MATH-650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13109557#comment-13109557
] 

Gilles commented on MATH-650:
-----------------------------

Revision 1173690 shows the resource approach to storing data.

It is still a little slower than literal arrays, but the gap is only about 12 ms now:
{noformat}
 compute   ~48 ms
 resources ~18 ms
 array      ~6 ms
{noformat}
In exchange for this (relative) slowness, the byte-code size is reduced by half and we can
have a "clean" source file. Moreover, we have a clear separation between code and data; the
latter is generated once and it would be easy to spot unwanted modification.

I think that even the smaller tables (sine, cosine, tangent) should also be stored in the
same way.


> 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
>         Attachments: FastMathLoadCheck.java, LucTestPerformance.java
>
>
> 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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