Integer logarithm of rational

[Bodigrim]

It would be desirable to have an integer logarithm on Rational:

rationalLogBase :: Rational -> Rational -> Int

[phadej]

This is less tricky (at least to specify), if one restricts base to > 1; even less trickier if also the n is >= 1 (but we can round towards zero) as in

Prelude> logBase 2 (4/10)
-1.3219280948873622
Prelude> logBase 2 (10/4)
1.3219280948873624

*Math.NumberTheory.Logarithms> rationalLogBase 2 (4/10)
-1
*Math.NumberTheory.Logarithms> rationalLogBase 2 (10/4)
1