- Overflow and underflow are not considered in all functions, which might
  lead to some infinite loops.
- Also, checks are not always made for intermediate over- or underflows, which
  may occur in the middle of the algorithms although the final result may be
  representable.
  For instance, if in the computation of Im (cos(x+i*y)) = -sin(x)*sinh(y)
  an overflow occurs in sinh(y), the value sign(Im (cos(x+i*y))) * inf
  is returned, even if sin(x) is sufficiently close to 0 such that
  sin(x)*sinh(y) is representable. If furthermore an underflow occurred
  in sin(x) (which has not been observed in practice), then the return
  value would be NaN*(+-inf)=NaN.

Currently, the following functions have been rewritten to solve these
problems:
mul, norm, sqr