[FFmpeg-devel] Help: AES GF Multiply

Reimar Döffinger Reimar.Doeffinger at gmx.de
Mon Jul 30 21:42:51 CEST 2012

On Mon, Jul 30, 2012 at 04:56:05PM +0200, Michael Niedermayer wrote:
> about aes.c, if you export the log8[] alog8[] (thats exp) tables
> it should be trivial to do a multiplication with them

You will also need to export an initialization function, at least it
seems not nice to depend on the full AES initialization.
And to simplify the whole mathematics to concrete usage, the
multiplication is:
alog8[log8[x] + log8[y]]
(assuming x and y != 0, if either is 0 the result is 0 as usual)
Doing it manually without the exponential/log lookup trick is
of course possible but quite a pain.

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