[Webkit-unassigned] [Bug 60396] Add RAII-style DenormalDisabler class to disable denormals which hurt audio performance

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=60396


Sam Weinig <sam at webkit.org> changed:

           What    |Removed                     |Added
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                 CC|                            |sam at webkit.org




--- Comment #14 from Sam Weinig <sam at webkit.org>  2011-05-09 16:14:10 PST ---
(In reply to comment #10)
> Oliver, I don't think a simple load will be any different.  Setting the denormal mask tells the processor to ignore any exceptions which occur due to any floating-point math which is dealing with denormals.  Not handling the exception causes a tiny amount of precision loss, which is acceptable for audio processing.  The performance benefit is very large because once these denormals get into a stateful audio processing algorithms they tend to stick around (in filter state, decaying delay lines, parameter slewing/de-glitching, etc.).  They can cause a very large number of exceptions to occur, causing enormous slowdown.
> 
> For all AudioUnits we used to disable them -- here's an old copy of an audio SDK file with this type of disabling (near the top of the file):
> http://www.google.com/codesearch/p?hl=en#9WNLlqRP2nE/trunk/PublicUtility/AUPublic/AUBase/AUBase.cpp&q=AUPublic&sa=N&cd=2&ct=rc

Can JavaScript run in the scope this is activated for?  If so, can the change in precision show up there?

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