[tremor] [PATCH] another additional 15% performance gain

[marc dukette]

I will check it out with PocketDivx as soon as the code is in CVS.  Sorry, I
don't have my box set up for handling .diff patches.

Sound like a great set of additions especially for use within video.  I will
look at the code, but how difficult would it be to have this as a parameter
of the library rather than a seperate recompile?  What I mean is is the code
spread out such that you would end up with nearly a complete dupicate of the
codebase.  it would be cool if we could turn this on or off based on
appication, so when playing video with low bitrate audio we could opt for
performance, while keeping highest quality for just audio playback.  I will
look at this when I get the code, but I wanted your initial take.

----- Original Message -----
From: "Nicolas Pitre" <nico at cam.org>
To: <tremor at xiph.org>
Cc: "Monty" <xiphmont at xiph.org>
Sent: Wednesday, October 09, 2002 2:29 PM
Subject: [tremor] [PATCH] another additional 15% performance gain

<p>>
> This is the completion of my 32 bit only multiply operation patch.  It is
> faster for sure but also less accurate than 64 bit multiplications.  Might
> be handy for slow CPUs or without native 64 bit multiplications, or for
> those out there with poor compilers (any EVC user wants to try out?).
>
> The patch adds a --enable-low-accuracy configure option so this is
> configurable before compiling.  For those not using the configure script
you
> need to globally define _LOW_ACCURACY_ to enable this feature.  Otherwise
> the resulting code remains just like before by default.
>
> Although the audio degradation is mostly inaudible it is still there
> nevertheless.  So this is not recommended if absolute high quality audio
is
> needed.  On the other hand some people will still find the audio quality
> more than acceptable for their use.  This is a price to pay for faster
code.
>
> With _LOW_ACCURACY_ enabled there was also a nice opportunity for text
size
> reduction:
>
> Default configuration:
>
>    text    data     bss     dec     hex filename
>   49607   45256    4160   99023   182cf ivorbisfile_example
>
> With ./configure --enable-low-accuracy:
>
>    text    data     bss     dec     hex filename
>   47655   14632    4160   66447   1038f ivorbisfile_example
>
> The patch is available from:
>
>
ftp://ftp.arm.linux.org.uk/pub/linux/arm/people/nico/vorbis/low_accuracy.dif
f.gz
>
> Although the patch itself is largish, the actual code addition is quite
> small.  The bulk of the patch consists of the addition of a X() on table
> values to preshift them when _LOW_ACCURACY_ is defined.
>
> I'd like to see this patch merged in the CVS at some point.  Monty?
>
>
> Nicolas
>
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