Re: [mpg123-devel] fixed point decoders

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

On 2009/06/01, at 21:37, Thomas Orgis wrote:

> Ah, now I can make sense out of this statement! I didn't look at a  
> non-sse build back then.
> Indeed, the situation on the Atlon XP is funny.
> Using  -msse -mfpmath=sse in CFLAGS makes the truncation code  
> faster... but it's again faster when dropping the -mfpmath=sse (I  
> did use blank CFLAGS before, so basically i386 code).
> Hm, so far the fastest build on the AthlonXP is achieved by using - 
> msse, but _not_ -mfpmath=sse, together with --enable-int-quality.
> Fastest & good rounding... well, that's the generic code... the SSE  
> code for non-quality rounding is significantly faster than anything  
> else.

The behavior when using -msse without --mfpmath=sse is: basic maths  
are done on x87 and fp-to-int truncations are done on SSE. And on  
Athlon, in most cases the x87 code is faster than the SSE code. So  
yeah, your findings are almost expected.

> Yes... the core2 should run on SSE. What really buggers me a bit is  
> that the generic code is about 2.5 times faster on the 1.466 GHz  
> AthlonXP compared to my mobile 1.2Ghz Core2duo. How can the latter  
> be that lame?
> I don't see the specs favouring the Athlon that much. Even the one  
> remaining memory channel (instead of two) of the Core2 should stil  
> be faster than what the Athlon has.
> Well, with your x86-64 SSE code, the Core2 catches up a bit... the  
> AthlonXP's SSE being just about 2.1 times faster. It seems like  
> Intel did some interesting cuts with this Core2 to make it power  
> efficient -- makes one wonder how well a die-shrinked Atlhon XP  
> would fare against it:-/

Hmm... Generally 1.2ghz core2 should run faster than 1.4ghz athlon. Is  
your core2 running in down-clocked mode, isn't it? I had a experience  
that a Pentium M didn't get a full speed when running a very short  
benchmark.

Thanks,
Taihei Monma