Notes of the libgcc-math BOF at the summit.

["Richard Guenther" <richard dot guenther at gmail dot com>]

Issues of providing both standard conforming and target optimized
math runtimes for GCC were discussed.

Interested parties are various frontends (C++, Fortran, Ada) that
are required to provide support similar to C99 from their runtime
and like to be able to fall back to a standard conforming implementation
provided by GCC.  Especially on weird target architectures and OSs
where the existing runtime is only partly working or cannot be relied
upon.

Other interest is from folks that require optimized versions of
the math runtime, being it for different ABI, stripped versions
useful for -ffast-math or -fno-math-errno.  In addition to that,
a place to add vectorized versions of the math routines, which
are closely integrated to GCC is requested.

Several points were be made about licensing, and people agreed
that while it may be possible to use the LGPL, using GPL + exception
will avoid user confusion and possible problems, especially if
we are going to automatically link against this library.

People had concerns about forking GNUs libm from glibc with respect
to maintainance issues.  The point was made that the standard
conforming runtime GCC would provide was optional and not to be used
if there is a conforming (and performant) runtime available from
glibc or the target.  Only the optimized routines would be used
on such systems, which of course, if target dependent would have
to be provided by the architecture maintainers if they want to enable
extra optimizations for their platform.

There were no doubts that we can get hands on properly licensed
(GPL + exception compatible) standard conforming C routines that
implement the C99 math runtime.  Offerings were from AMD, and
the original BSD-licensed routines from SUN were mentioned.  Also
it was suggested IBM could re-submit their math library for use
in GCC with a GPL + exception license.

--

In conclusion, having a C99 math runtime subject to GPL + exception
inside GCC alongside with whatever optimized routines (being able
to base on the C routines provided by the C99 routines) was generally
accepted as worthwhile.


Thanks,
Richard.

PS: please direct discussion to gcc@gcc.gnu.org only and avoid
cross-posting followups.