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From "Luc Maisonobe (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-650) FastMath has static code which slows the first access to FastMath
Date Sat, 11 Feb 2012 12:43:59 GMT

    [ https://issues.apache.org/jira/browse/MATH-650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13206095#comment-13206095
] 

Luc Maisonobe commented on MATH-650:
------------------------------------

I would like to resolve this issue.
I think everybody agreed pre-computation was an improvement, and the remaining discussions
are about the way the pre-computed tables are loaded. We have two competing implementations
for that: resources loaded from a binary file and literal arrays compiled in the library.
In both cases, the data is generated beforehand by our own code, so in both case users who
wants to re-generate with different settings them can do so.

The advantages of resources are that they are more compact (binary) and don't clutter the
sources with large tables.
The advantages of literal arrays are that the can be checked by mere human beings and don't
require any support code.
The speed difference between the two implementation exists but is tiny.

Two people have already expressed their preferences (one favoring resources the other one
favoring literal arrays). I don't have a clear cut preference myself (only a slight bias toward
one solution which I prefer to keep for myself).

I would like to have the opinions of newer developers and users on this before selecting one
approach. Could someone please provide another opinion ?
                
> 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
>             Fix For: 3.0
>
>         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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