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https://issues.apache.org/jira/browse/MATH-841?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13429479#comment-13429479
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Gilles commented on MATH-841:
-----------------------------
{noformat}
gcd (calls per timed block: 100000, timed blocks: 100, time unit: ms)
name time/call std error total time ratio
difference
Math841 (v1) 1.54124193e-04 1.59358522e-05 1.5412e+03 1.0000e+00
0.00000000e+00
Math841 (v2) 1.30920278e-04 1.90623800e-05 1.3092e+03 8.4945e-01
-2.32039150e+02
ArithmeticUtils 3.03674885e-04 1.47818091e-05 3.0367e+03 1.9703e+00
1.49550692e+03
{noformat}
An additional 15% improvement.
Just to be sure: Is it allowed to take Guava's implementation?
> gcd speed up
> ------------
>
> Key: MATH-841
> URL: https://issues.apache.org/jira/browse/MATH-841
> Project: Commons Math
> Issue Type: Improvement
> Affects Versions: 3.0
> Environment: ubuntu 32bits/intel-i5/java6
> Reporter: Sebastien Riou
> Priority: Trivial
> Labels: patch, performance
> Fix For: 3.1
>
> Attachments: ArithmeticUtils.java, patchGcdInt2.txt
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> The gcd(int,int) method of ArithmeticUtils seems 2 times slower than the
> naive approach using modulo operator. The following test code runs in 11s
> with current version and in 6s with the patch.
> public void testApache(){
> Random rng=new Random(0);
> long checksum=0;
> long start=System.nanoTime();
> checksum+=gcd(0,Integer.MAX_VALUE);
> checksum+=gcd(Integer.MAX_VALUE,0);
> checksum+=gcd(Integer.MAX_VALUE,rng.nextInt());
> for(int i=0;i<10000;i++)
> checksum+=gcd(rng.nextInt(),Integer.MAX_VALUE);
> checksum+=gcd(Integer.MAX_VALUE,Integer.MAX_VALUE);
> checksum+=gcd(Integer.MIN_VALUE,1<<30);
> checksum+=gcd(1<<30,1<<30);
> checksum+=gcd(3 * (1<<20),9 * (1<<15));
> for(int i=0;i<30000000;i++)
> checksum+=gcd(rng.nextInt(),rng.nextInt());
> long end=System.nanoTime();
> long tns=end-start;
> long tms=(tns+500000)/1000000;
> long ts=(tms+500)/1000;
> System.out.println("exec time="+ts+"s, ("+tms+"ms),
> checksum="+checksum);
> assertEquals(9023314441L,checksum);
> }
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