Actually gcc provides libquadmath for 128-bit floating point math routines.
It might be worth a look.
Aloha
Kai
Am 20.07.2013 17:04 schrieb "JonY" <[email protected]>:
> On 7/21/2013 01:58, K. Frank wrote:
> >
> > That would certainly make sense, but it doesn't square with what
> > numeric_limits is telling me:
> >
> > numeric_limits<long double>::digits10 = 18
> > numeric_limits<long double>::max_digits10 = 21
> >
> > Just to check that numeric_limits isn't lying to me I ran a small program
> > that adds and subtracts 1.0 to and from a small long double. This agrees
> > with numeric_limits and shows about 20 decimal digits of precision.
> >
> > ---------------
> > d = 1e-017
> > (d += 1.0; d -= 1.0;)
> > d = 9.97466e-018
> > ---------------
> > d = 1e-018
> > (d += 1.0; d -= 1.0;)
> > d = 9.75782e-019
> > ---------------
> > d = 1e-019
> > (d += 1.0; d -= 1.0;)
> > d = 1.0842e-019
> > ---------------
> > d = 1e-020
> > (d += 1.0; d -= 1.0;)
> > d = 0
> > ---------------
> >
> > I compiled the test program without any special compiler flags. Do I
> > need to somehow enable the SSE registers you mentioned in order
> > to take advantage of them?
> >
>
> I checked the assembly listing and have confirmed that GCC still tries
> to use the 387 for extended precision and will use SSE for double
> precision.
>
> IIRC AMD's 387 implementation is 64bit only, so your results might
> differ on them.
>
> >> Use something like MPFR if you want arbitrary high precision math
> >> independent of hardware capabilities.
> >
> > No, I don't need that. I was just a little curious about what I saw, and
> > thought an 80-bit long double was a little skimpy for a modern, 64-bit
> > machine.
>
> There is quad precision floats with 128-bit lengths, they're not very
> commonly supported. GCC supports it, but aren't any math routines in
> mingw-w64 to actually work on it, eg quad sqrt etc.
>
> There is also decimal math support in GCC, there is some work on the
> math routines, but nothing yet for general use.
>
>
>
>
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