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Re: [xmlvm-users] Arrays manipulation on iPhone
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From: Jacob N. <jac...@gm...> - 2009-09-21 07:30:24
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Hello Sascha,
thanks for your quick reply.
In our case the hope was to use 170 hours on preparing and porting our Java
code, withing one calendar month.
We have now changed that estimate to the double - 340 hours, within 1 1/2
calendar month.
We are proficient Java coders (Objective-C is new, but for array
manopulations it probably wouldnt seem to give too much headache :-) and one
(I) has understanding of XML, bytecode and virtual machines. I could
allocate up to 60 hours for improving XMLVM during the next month if that
could solve our problems.
I know 60 hours isnt much, but as economy is a concern here must weight it
against finding another way of porting the application (eventually by hand).
If you, within these time contraint, would recommend spending some time
improving XMLVM and your'e willing to guide me and engage yourselves in the
project too, then lets consider it.
However, it seems to me that there is another performance problem here, and
that is the usage of NSMutableArray of objects instead of a byte[] array ?
I would be very thankfull if you could comment with your best guess on,
whether the factor 20 somes from the stack-based model used for generating
Objective-C code, or from the usage of NSMutableArray of objects instead of
byte[] arrays?
Another important questions is then: How much effort would be required to
make a version of XMLVM that generated code using arrays of simple type
instead of arrays ?
Thank you,
Jacob
2009/9/21 Sascha Haeberling <sa...@xm...>
> Hello Jacob,
> thank you for your great analysis and question.
>
> You are absolutely right. As you can see, we are trying to mimic a JVM as
> close as possible. While we think that the performance is fine for most use
> cases, some use cases (like yours) can actually perform much worse when
> being cross-compiled with XMLVM. Therefore, one of our current tasks is to
> look at converting our stack-bases model to a register-based one, so that
> languages like Objective-C can benefit.
>
> However, we are still in the planning stage of this and I cannot give you
> any deadlines. Would this be something you are interested in contributing to
> or do you have any other ideas?
>
> Thank you
> // Sascha
>
> On Sun, Sep 20, 2009 at 11:29 PM, Jacob Nordfalk <jac...@gm...
> > wrote:
>
>> Hi,
>>
>> I am considering porting an image manipulation program in Java to iPhone
>> using XMLVM.
>>
>> However, code such as
>>
>> public byte[] xxx(byte[] rgb) {
>>
>> for (int i = 0; i<rgb.length; i+=3) {
>> rgb[i] += 1;
>> rgb[i+1]/=2;
>> rgb[i+2]/=2;
>> }
>>
>> return rgb;
>> }
>>
>> seems to run 20 times slower than JIT-enabled Java when compiling xmlvm
>> generated objective-C.
>>
>> When I looked at the code I understood why - the generated objective-C is
>> something like 26 lines
>> per line of Java (here below is for the line: rgb[i+1]/=2).
>>
>>
>> - (NSMutableArray*) optimize___byte_ARRAYTYPE :(NSMutableArray*)n1
>> {
>> XMLVMElem _stack[4];
>> XMLVMElem _locals[5];
>> int _sp = 0;
>> XMLVMElem _op1, _op2, _op3;
>> ...
>>
>> *// rgb[i+1]/=2;*
>> _stack[_sp++].o = _locals[1].o;
>> _op1.i = _locals[4].i;
>> _stack[_sp++].i = _op1.i;
>> _stack[_sp++].i = 1;
>> _op2.i = _stack[--_sp].i;
>> _op1.i = _stack[--_sp].i;
>> _stack[_sp++].i = _op1.i + _op2.i;
>> _op1 = _stack[_sp - 2];
>> _op2 = _stack[_sp - 1];
>> _stack[_sp++] = _op1;
>> _stack[_sp++] = _op2;
>> _op1.i = _stack[--_sp].i;
>> _op2.o = _stack[--_sp].o;
>> _stack[_sp++].i = [[_op2.o objectAtIndex: _op1.i] intValue];
>> _stack[_sp++].i = 2;
>> _op2.i = _stack[--_sp].i;
>> _op1.i = _stack[--_sp].i;
>> _stack[_sp++].i = _op1.i / _op2.i;
>> _op1.i = _stack[--_sp].i;
>> _stack[_sp++].i = (int) (_op1.i & 0xFF);
>> _op1.i = _stack[--_sp].i;
>> _op2.i = _stack[--_sp].i;
>> _op3.o = _stack[--_sp].o;
>> [_op3.o replaceObjectAtIndex: _op2.i withObject: [NSNumber
>> numberWithInt: _op1.i]];
>>
>>
>> Now, I understand that the speed factor 20 is becaurse XMLVM is emulating
>> the stack-based JVM in Objective-C,
>> but I as I have really LOT of array manipulation code I am asking you:
>>
>>
>> Do you have any advice or ideas on how to make Java code using simple
>> array manipulations run relatively fast on the iPhone ?
>>
>>
>>
>> Thanks you,
>> Jacob Nordfalk
>>
>> --
>> Jacob Nordfalk
>> एस्पेरान्तो के हो? http://www.esperanto.org.np/.
>> Memoraĵoj de KEF -. http://kef.saluton.dk/memorajoj/
>>
>>
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>>
>
--
Jacob Nordfalk
एस्पेरान्तो के हो? http://www.esperanto.org.np/.
Memoraĵoj de KEF -. http://kef.saluton.dk/memorajoj/
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