[Ffmpeg-devel] [PATCH] 2 % faster wma_decode_block and float removal

Michael Niedermayer michaelni
Sun Mar 5 21:36:29 CET 2006


On Sun, Mar 05, 2006 at 08:43:49PM +0000, Benjamin Larsson wrote:
> This patch replaces some pow calculations with precalculated tables and
> some float to fixedpoint conversion in the init.

ok, here are a few questions and issues which MUST be dealt with before
theres any hope to apply this

1. why should we remove floats in the init code, it makes the code less
2. some results from float computations are feed into if(x>1.23) style code
   differnt rounding from integer math will probably cause serious issues,
   again this is init code, where speed is irrelevant 
3. every change which does not lead to binary identical decoding must be 
   tested with some testsamples (max difference, mean squared error, PSNR)
   i know from messing with the mp3 decoder that tiny changes (32bit vs. 64bit
   multiplies at the wrong spot) do lead to audible issues
   (basically expect anything which is non optional and causes >+-1 max error 
   to be rejected)



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