I've been looking at the prevpow/nextpow functions, and they seem somewhat broken to me:

• nextpow2(n) != nextpow2(2, n): the former returns the power-of-2 value, and the latter returns the exponent. e.g. nextpow2(9) is 16, but nextpow(2, 9) is 4. Similarly for prevpow.
• nextpow2(0) == prevpow2(0) == 0. I can only understand this behavior under the theory that zero is 2^–∞, but that seems questionable to me. nextpow(2, 0) and prevpow(2, 0) raise an InexactError (I would have expected a DomainError, maybe?).
• prevpow(2, 1) correctly returns 0 (1 == 2^0, see first point), but nextpow(2, 1) throws a DomainError, which is certainly wrong.
• nextpow(2, -7) and prevpow(2, -7) raise DomainErrors, but nextpow2(-7) gives -8 and prevpow2(-7) gives -4.
• The documentation for these functions does not clarify any of the above behaviors.