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# Re: libjava configure question

Tom Tromey writes:
> >>>>> "Andrew" == Andrew Haley <aph@redhat.com> writes:
>
> Andrew> One other thing: I don't think we can do this in general and meet even
> Andrew> the more relaxed requirements of java.lang.Math, because the x86 has a
> Andrew> restricted range of allowable arguments to its trig functions.
>
> I thought the Math restrictions were designed to explicitly allow use
> of the FPU on x86.
Yes, but not without some wrapper code. The crucial issue here is
full range reduction, and the floating-point instructions don't do
that by themselves.
> BTW, with 1.5 we will have more opportunities to use builtins here.
> For floating point there is at least cbrt; for integer types there
> is popcount and (I think) a few more bit-twiddling operations.
>
> Andrew> Try this with -ffast-math:
>
> I thought -ffast-math turned on some unsafe optimizations. The
> manual is really unclear about what it does though. Are our FP
> builtins conditional on -ffast-math?
In this particular case, the use of floating-point trig instructions
is enabled by -ffast-math.
Andrew.