[SDL] patch for SDL sound mixing

[Sam Lantinga]

> Hi,

> I've made a patch with my SDL modification. I think it's ready to go 
> into cvs (I've have been using it for some months, and without problems).
> The speedup is noticable, especially when you mix many sound channels 
> together. For example, in a game I'm writing cpu usage for the sound 
> thread goes from 6% to 2-3%.

Looks great, I've added your code to CVS.  Thanks!

> PS : I also have some mmx code for the sound conversion functions, but I 
> was wondering if it could provide some speed-up at run time (or just  at 
> start up). Any opinions ?

Feel free to post it, I'm sure someone can use it.

See ya!
	-Sam Lantinga, Software Engineer, Blizzard Entertainment