NOTE: The new, authoritative, location for this package is https://github.com/JuliaMath/ILog2.jl
This package provides a fast implementation of the integer-valued, base-2 logarithm.
ilog2 supports other types of numbers, as well. It also provides checkispow2.
ilog2(n::Real) compute the largest m such that 2^m <= n.
ilog2(n::Real, RoundUp) compute the smallest m such that 2^m >= n.
checkispow2(n::Number) returns ilog2(n) if n is a power of two.
Otherwise throws a DomainError.