Optimizations for very long numbers:
- optimize multiplication FFT
- division, e.g. as in Knuth
- recursive Euklid-Lehmer or Binary-Weber algorithms,
- reciprocal, Newton x -> x (2 - a x)
- division
- radix conversion
- log, exp, sin, cos, etc. as in [Brent] or [Borwein^2: pi and the AGM]

