Bug#318959: libc6: unreproducible on powerpc

[GOTO Masanori <gotom@debian.or.jp>]

tags 318959 -unreproducible
tags 318959 -moreinfo
tags 318959 +confirmed
severity 318959 important
retitle 318959 gcc-4.0 gives wrong results for lround
thanks

At Mon, 25 Jul 2005 11:37:59 +0200,
g.bonacci@libero.it wrote:
> - Undefined behaviour is very likely to depend on compiler optimization
>   options, and that explains the "mysterious behaviour" previously
>   reported.  Probably with '-O1' and above the compiler skips the
>   computation at all, and places 0.

Thanks for your following up, you're absolutely right.  I confirmed
the problem.  We'll put new glibc 2.3.5 soon, so I downgrade it to
important, but I'll check it.

> - I don't know how uint32_t are aligned and operated on in powerpc/64
>   archs, but maybe different alignment (and different "undefined
>   behaviour") is the reason why Paul could not reproduce the bug.
>   BTW, what arch did you run your tests on, GOTO?
>
> I don't know ieee754, so I don't dare submit a patch to libc (e.g., if
> (52 - j0) > 31, use 0), but I believe dropping this bug as unreproducible
> would be a mistake.  Better downgrade it and forward upstream.  It reminds
> me of the fdiv bug in early pentiums.

I tested it on *ppc* because I didn't read the ex-reassigned messages.
Actually ppc uses the different lround function.

Regards,
-- gotom