Math trig intrinsics and compiler options

[gustav trede]

2009/7/16 gustav trede <gustav.trede at gmail.com>

>
>
> 2009/7/16 Christian Thalinger <Christian.Thalinger at sun.com>
>
> Azeem Jiva wrote:
>> > Joe,
>> >   Gustav sent me an email asking for help with the intrinsification of
>> > the trig functions and a suggestion I gave him was to not call
>> > fsin/fcos/ftan since those instructions are microcoded on Intel/AMD
>> > hardware and very slow.  Slower than the call to
>> > sharedRuntimeTrig.cpp, and in all cases it's best to stay away from
>> > the hardware instructions.
>>
>> I just did some micro-benchmarking on an Intel Core2 Duo and in the
>> range of [0,2pi) inlining the hardware instructions is slightly faster
>> (about 2.5%).  Limiting the range to [0,pi/4) (means no runtime calls)
>> hardware instructions are 1.5x faster.
>>
>> I think we should keep the current approach.
>>
>> -- Christian
>>
>
>
on opensolaris 118 x64 core2  with the patch applied i get 44 cycles  as
cost per  Math cos , sin on average, including the loop overhead for the 0
to PI/4 range .

what cost do you get with fcos , fsin  in this test ? :


    private void dotest(final double start, final double end){
            final int innerIter = 150000;
            final int iter = 5000;
            double ret = 0;
            long t1= System.nanoTime();
            for (int i=0;i<iter;i++)
                ret+=trigcalc(start, end, innerIter);
            double tsmall= ((System.nanoTime()-t1)/(2.0d*iter*innerIter));
            double Mpersec = ((int)(100000 / tsmall))/100d;
            System.out.println(""+start+" to "+end+" : "+ Mpersec+"
millions/sec , ret:"+ret);
    }


    private double trigcalc(final double start, final double end, final int
innerIter){
        double ret = 0;
        double delta = (end-start)/innerIter;
        for (double i=start;i<end;i+=delta ){
            ret += Math.sin(i)+Math.cos(i);
        }
        return ret;
    }







-- 
regards
 gustav trede
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