Re: powerpc-g++ 4.2.4 problem casting long long to double

[Gary Thomas <gary@mlbassoc.com>]

On 05/19/2010 03:38 AM, Vitus Jensen wrote:
> Hello!
>
> We noticed a strange problem with C++ code casting long long variables
> to double, as a lot of qt-embedded code is doing.
>
> =================
> double
> convert(long long l)
> {
> return (double)l; // or double(l)
> }
>
> int
> main(int argc, char * argv[])
> {
> long long l = 10;
> double f;
>
> f = convert(l);
> printf("convert: %lld => %f\n", l, f);
> return 0;
> }
> ====================
>
> output:
> convert: 10 => 0.000000
>
> C++ compiled via powerpc-angstrom-linux-g++ gives the above result.
> Compiling the same code as C using powerpc-angstrom-linux-gcc works
> fine. But when looking at the assembler code both compiler produce
> virtually identical output and both call __floatdidf to do the actual
> conversion. Very strange, has anyone ever seen similar effects?

Is this from a recent tree (i.e. post Richard Purdie's restructuring)?

I've seen similar problems with C++ code on Poky which uses the same changes.

>
> MACHINE bluepro (ppc603e, used in n1200, efika, lite5200, storcenter)
> DISTRO angstrom
> BRANCH stable
>
> Openembedded is used to build images and QT4 SDKs for this machine which
> work fine otherwise. The compiler version used is the default for
> angstrom (4.2.4), that default and the gcc recipe is identical between
> stable and dev branches.
>
> ppc405 uses the older 4.1.1 gcc which shows the identical behaviour when
> selected via ANGSTROM_GCC_VERSION. 4.3.2 and 4.3.3 failed to link but
> created the same assembler code otherwise.
>
> How can I analyse this situation further? I'm particular interested in
> how different __floatdidf versions get used dependend on frontend, the
> source of __floatdidf is in the gcc sourcetree and I expected it to be
> compiled just once.
>
> Vitus
>
>
> PS: fp-int-convert-long-double.c from the testsuite fails too, if
> compiled via powerpc-angstrom-linux-g++
>

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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