Re: [mpg123-devel] fixed point decoders

[Taihei M. <tm...@ma...>]

On 2009/06/01, at 17:46, Thomas Orgis wrote:

> But, looking at the performance front, I got very confused: On an  
> Athlon XP, the int-quality fpu code is _a_lot_ faster than the  
> normal truncating fpu code!
> I got 2.9s runtime vs. 3.9s . On my core2duo, the truncation code as  
> a bit of a lead as we knew before.
> But I don't quite understand what's happening on the AthlonXP.  
> Really strange... but I really cannot work on this today. Things to  
> do.

Well, that's expected. As I said before,

> And I noticed that this method is about 10% (!) faster than the
> simple rounding with truncation on x87 fpu (my mistake, fisttp is
> only available on SSE3-capable cpus).


on x87 FPU simple truncation is slow. But on SSE FPU truncation is  
fast, because it is doable with just one instruction. Probably you are  
using SSE FPU (it is default on x86-64) on your core2.

Thanks,
Taihei Monma