Floating point emulation

Yves Rutschle y.rutschle@indigovision.com
Mon Dec 2 08:08:00 GMT 2002

On Mon, Dec 02, 2002 at 10:49:57AM -0500, Peter Barada wrote:
> >(Incidently, if you are compiling with -msoft-float, I don't
> >expect that using doubles will "increase performance", as
> >you'll double the amount of work the processor has to do...)
> It all depends on the hardware implementation of the FPU.  If the FPU
> can only operate in double precision, then to properly model single
> precision operations requires rounding instructions to be added after
> every operation to force the final result to appear as if it was
> calculated in single precision.  This can indeed slow it down.

Interesting.. But that has to be expected every time you use
hardware in a manner that it wasn't indended for (same
story, it's not easier to play at 8KHz on a DSP that only
supports 24KHz...). 

However, I was talking about code compiled with
-msoft-float... where arguably all operations are performed
with many cycles by the non-floating-point-enable CPU...
Then it should always be slower to use double than single?
(if double is indeed bigger than single, as pointed out in
Kai's other posting on the subject).


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