[Ffmpeg-devel] Fixed vs. Floating Point AAC

Rich Felker dalias
Thu Mar 9 01:38:22 CET 2006

On Thu, Mar 09, 2006 at 12:37:05AM +0100, Michael Niedermayer wrote:
> but what about the dynamic range? if all samples are 1.0 (max) then a
> dc component would have a value of N^0.5 which for lets say N=1024 would
> be 32, so we would need 21 bits, wheres the problem now, 21bits * 21bits=
> 42bits and that doesnt fit in 32bits so no fast 32*32->32bit muliplies 

A 32*32 multiply gives a 64bit result. This is fast. If a cpu sucks
too much to give the full result, that's the particular platform's
problem and users who insist on using a broken cpu arch will have to
deal with it being somewhat slower. x86 does it correctly, and has
done so ever since the 8088...


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