[kaffe] Re: Classpath's doubleToLongBits

[Dalibor Topic]

Christian Thalinger schrieb:
> On Mon, 2008-02-18 at 04:03 +0100, Dalibor Topic wrote:
>   
>> This one turned out to be a lot more fun to track down.
>>
>> It's pretty easy to rewrite the test whether to swap words in a jdouble: 
>> put -0.0 into a jvalue's
>> jdouble element, and if the correspoding jlong bitstream is > 0, you 
>> have to swap the words.
>> It's a way of dynamically doing what the fdlibm #defines do, but it 
>> works out the same way:
>> swap on arm-debian-oabi.
>>
>> But that didn't fix the breakage.
>>
>> So I played around some more, and eventually, it turned out that kaffe's 
>> classfile constant parser
>> was working fine, and I was reading in doubles the way arm's FPU 
>> expected them laid out, it
>> turned out the interpreter was working ok, too, and so on.
>>
>> But the breakage was still there.
>>
>> Turning the way, for example, the double constants were parsed around, 
>> and doing it the 'wrong' way,
>> fixed some regression tests, but broke others. Similarly, reassembling 
>> doubles in the interpreter
>> from words the 'wrong' way had the same effect with other tests.
>>
>> So I had to examine things a bit more closely with jcf-dump. It turned 
>> out that, since I was using a
>> glibj.zip compiled on an x86-linux host, the constant in the class 
>> java.lang.Double were laid out
>> correctly. But in the tests classes compiled on the arm-oabi-linux 
>> platform using ecj on gcj-4.3,
>> double constants were laid out incorrectly, with their words swapped, as 
>> a comparison with the
>> tests compiled on x86-linux with ecj on gcj showed.
>>
>> So, current Kaffe CVS head interpreter works on arm-oabi-linux without 
>> regressions. The regressions
>> Kiyo-san has seen are caused by buggy compilers (jikes / ecj on gcj). 
>> And I'll move on to comitting the
>> jit patches for arm-linux next.
>>     
>
> That sounds like it was a lot of work.  Did you change anything new in
> GNU Classpath or should I test the current CVS version
I wrote a patch using the -0.0d > 0L hack described above to detect 
whether we should switch words
in a double, but it turned out not to be necessary, so current CVS is 
fine (and contains no related changes).

cheers,
dalibor topic