log2f
=====

POSIX specification:
 https://pubs.opengroup.org/onlinepubs/9699919799/functions/log2f.html

Gnulib module: log2f or log2f-ieee

Portability problems fixed by either Gnulib module log2f or log2f-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, Android 4.2.

  * 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 slightly wrong values for exact powers of 2 on some platforms: Cygwin 1.7.9.

Portability problems fixed by Gnulib module log2f-ieee:

  * This function returns a wrong value for a negative argument on some platforms: NetBSD 5.1, Solaris 10/x86_64.

Portability problems not fixed by Gnulib: