Mixing hard and soft floating point?

Joakim Tjernlund joakim.tjernlund at transmode.se
Sun Oct 18 05:24:05 EST 2009

Wolfgang Denk <wd at denx.de> wrote on 17/10/2009 20:12:24:
> Dear Joakim Tjernlund,
> In message <OFC920E57F.DFABC29F-ONC1257652.00421E11-C1257652.
> 0043478A at transmode.se> you wrote:
> >
> > Anyone tried mixing hard and soft FP in on soft float CPU such as 83xx?
> Hm... most 83xx have a FPU.

Yeah, I meant 832x. These don't have a FPU

> > Been trying to figure out if this is a good idea or not.
> > Any combinations that will or won't work?
> What exactly do you mean by "mixing"? You cannot (at least not with
> any reasonable effort) mix hard and soft FP in the same application /
> linked object. And it would be pretty difficult to setup separate
> libraries for and all that stuff for both hard and soft FP binaries
> in one system.

I meant on per app or per lib basis, not within the same

> I doubt if such a setup makes sense at all.
> > Generally I got soft FP in all system libs but there might be
> > an binary application which will use hard FP.
> Recompile and relink it with soft-fp as well. Or ask the provider to
> do that.

That is what I am trying do/find out. The supplier claims that
it should not be a problem and is ATM unwilling to recompile the app/libs.
I am not convinced won't cause problems, not to mention performance degradation.

> > Is the MATH_EMU option in the kernel reliable(for 8xx too)?
> It's reliable enough to install and run standard  distributions  like
> Debian, Ubuntu, or Fedora, but I have to admit that we haven't stress
> tested any special FP test suites in such an environment. In everyday
> use I didn't see any real issues, though.

OK, but then you don't mix some libs/apps with soft and other
apps/libs with hard FP?


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