9.524 log2

POSIX specification:
http://www.opengroup.org/onlinepubs/9699919799/functions/log2.html

Gnulib module: log2 or log2-ieee

Portability problems fixed by either Gnulib module log2 or log2-ieee:

• This function is missing on some platforms: FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, older IRIX 6.5, Solaris 9, MSVC 9, Interix 3.5.
• This function is not declared on some platforms: IRIX 6.5.
• This function is only provided as a macro on some platforms: Cygwin 1.5.x.
• This function returns a wrong value for a minus zero argument on some platforms: OSF/1 5.1.
• This function returns slightly wrong values for exact powers of 2 on some platforms: Cygwin 1.7.9.

Portability problems fixed by Gnulib module log2-ieee:

• This function returns a wrong value for a negative argument on some platforms: NetBSD 5.1, Solaris 11 2011-11.

Portability problems not fixed by Gnulib: