This replaces the periodic recalculation of error correlations and the syndrome
by in-place modification. Bit flip is therefore a bit slower, but overall
decoding of the 256-bit secure variant fits in 200ms, and 128-bit variant
decodes under 20ms.
There still could be some (blatantly nondeterministic) method to do this using
FFT, research underway.
Mirek Kratochvil