Re: [CFT]: ClangBSD is selfhosting, we need testers now

On Sun, Apr 25, 2010 at 12:06:49PM +0200, Alexander Best wrote:
> i was able to pinpoint the
> exact function which is causing the problem:
> 
> it's snd_xbytes().

This is an odd-looking function.  Its purpose is to compute the
size of a target buffer for a block of audio samples that might
be sample-rate-converted or format changed.  It has a loop to
compute the gcd of the second two arguments (from, to), so that
it can divide by that common factor so that it can then do v *
(to/x) / (from/x).  It's not immediately obvious to me why it
bothers to find the gcd, since the division by the original
from should work anyway, as it's using a 64-bit numerator...

The only difference that I can see when this is compiled with cc
vs clang on my amd64 system is that the latter uses a divq in
the loop and the former uses a divl.  I haven't figured out why,
yet.  Hmm.  If the same division logic is being used in the i386
version of clang, then it's possible that this is resulting in
a call to an extended precision divide subroutine, which could
slow things down a bit.

Cheers,

-- 
Andrew