log returns the logarithm of number in base base.
If base is not supplied its value is e,
the base of the natural logarithms.
log may return a complex when given a
(log -1.0) ==(complex 0.0 (float pi 0.0))
If base is zero,
log returns zero.
The result of (log 8 2) may be either 3 or 3.0, depending on the
implementation. An implementation can use floating-point calculations
even if an exact integer result is possible.
The branch cut for the logarithm function of one argument (natural
logarithm) lies along the negative real axis, continuous with quadrant II.
The domain excludes the origin.
The mathematical definition of a complex logarithm
is as follows, whether or not minus zero is supported by the
(log x) ==(complex (log (abs x)) (phase x))
Therefore the range of the one-argument logarithm function is that strip
of the complex plane containing numbers with imaginary parts between
- pi (exclusive) and pi (inclusive) if minus zero is not supported,
or - pi (inclusive) and pi (inclusive) if minus zero is supported.
The two-argument logarithm function is defined as
(log base number)
==(/ (log number) (log base))
This defines the principal values precisely.
The range of the two-argument logarithm function is the entire complex plane.