>I'm lost, that's why i decide to look for another fft in the mean time
>or perhaps another cosine table that gives me no such errors.

You do realise that a Cosine table only needs to have data for 90 degrees,
and the other 270 degrees can be worked out by using the correct quadrant
adjustment.

I do not know anything about the internals of FFT's, but is there any way
you can use this sort of symmetry inside the FFT?

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