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

while I agree that the function is strange there indeed is a bug
in llvm. See: http://llvm.org/bugs/show_bug.cgi?id=6941

On Tue, Apr 27, 2010 at 02:50:53PM +1000, Andrew Reilly wrote:
> 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