Do everything in Java…

[John Colvin via Digitalmars-d]

On Sunday, 7 December 2014 at 22:46:02 UTC, Dmitry Olshansky 
wrote:
> 08-Dec-2014 01:38, John Colvin пишет:
>> On Sunday, 7 December 2014 at 22:13:50 UTC, Dmitry Olshansky 
>> wrote:
>>> 08-Dec-2014 00:36, John Colvin пишет:
>>>> On Sunday, 7 December 2014 at 19:56:49 UTC, Dmitry Olshansky 
>>>> wrote:
>>>>> 06-Dec-2014 18:33, H. S. Teoh via Digitalmars-d пишет:
>>>>>> On Sat, Dec 06, 2014 at 03:26:08PM +0000, Russel Winder via
>>>>>> Digitalmars-d wrote:
>>>>>> [...]
>>>>>>>>  primitive are passed by value; arrays and user defined 
>>>>>>>> types are
>>>>>>>> passed by reference only (killing memory usage)
>>>>>>>
>>>>>>> Primitive types are scheduled for removal, leaving only 
>>>>>>> reference
>>>>>>> types.
>>>>>> [...]
>>>>>>
>>>>>> Whoa. So they're basically going to rely on JIT to convert 
>>>>>> those boxed
>>>>>> Integers into hardware ints for performance?
>>>>>
>>>>> With great success.
>>>>>
>>>>>> Sounds like I will never
>>>>>> consider Java for computation-heavy tasks then...
>>>>>
>>>>> Interestingly working with JVM for the last 2 years the 
>>>>> only problem
>>>>> I've found is memory usage overhead of collections and 
>>>>> non-trivial
>>>>> objects. In my tests performance of simple numeric code was 
>>>>> actually
>>>>> better with Scala (not even plain Java) then with D (LDC), 
>>>>> for
>>>>> instance.
>>>>
>>>> Got an example? I'd be interested to see a numerical-code 
>>>> example where
>>>> the JVM can beat the llvm/gcc backends on a real calculation 
>>>> (even if
>>>> it's a small one).
>>>
>>> It was trivial Gaussian integration.
>>> http://en.wikipedia.org/wiki/Gaussian_quadrature
>>>
>>> I do not claim code is optimal or anything, but it's line for 
>>> line.
>>>
>
> [snip]
>
>> on my machine (Haswell i5) I get scala as taking 1.6x as long 
>> as the ldc
>> version.
>>
>> I don't know scala though, I compiled using -optimise, are 
>> there other
>> arguments I should be using?
>
> There is no point in -optimise at least I do not recall using 
> it.
> What's your JVM ? It should be Oracle's HotSpot not OpenJDK.

hotspot.

After changing the benchmark to more carefully measure the 
integration function (ldc was unfairly taking advantage of 
knowing a and b at compile-time), scala does indeed win by a 
small margin.

I wonder what it's managing to achieve here? AFAICT there really 
isn't much scope for optimisation in that while loop without 
breaking IEEE-754 guarantees.