Use generic fdim on more architectures (bug 6796, bug 20255, bug 20256).

Some architectures have their own versions of fdim functions, which
are missing errno setting (bug 6796) and may also return sNaN instead
of qNaN for sNaN input, in the case of the x86 / x86_64 long double
versions (bug 20256).

These versions are not actually doing anything that a compiler
couldn't generate, just straightforward comparisons / arithmetic (and,
in the x86 / x86_64 case, testing for NaNs with fxam, which isn't
actually needed once you use an unordered comparison and let the NaNs
pass through the same subtraction as non-NaN inputs).  This patch
removes the x86 / x86_64 / powerpc versions, so that those
architectures use the generic C versions, which correctly handle
setting errno and deal properly with sNaN inputs.  This seems better
than dealing with setting errno in lots of .S versions.

The i386 versions also return results with excess range and precision,
which is not appropriate for a function exactly defined by reference
to IEEE operations.  For errno setting to work correctly on overflow,
it's necessary to remove excess range with math_narrow_eval, which
this patch duly does in the float and double versions so that the
tests can reliably pass on x86.  For float, this avoids any double
rounding issues as the long double precision is more than twice that
of float.  For double, double rounding issues will need to be
addressed separately, so this patch does not fully fix bug 20255.

Tested for x86_64, x86 and powerpc.

	[BZ #6796]
	[BZ #20255]
	[BZ #20256]
	* math/s_fdim.c: Include <math_private.h>.
	(__fdim): Use math_narrow_eval on result.
	* math/s_fdimf.c: Include <math_private.h>.
	(__fdimf): Use math_narrow_eval on result.
	* sysdeps/i386/fpu/s_fdim.S: Remove file.
	* sysdeps/i386/fpu/s_fdimf.S: Likewise.
	* sysdeps/i386/fpu/s_fdiml.S: Likewise.
	* sysdeps/i386/i686/fpu/s_fdim.S: Likewise.
	* sysdeps/i386/i686/fpu/s_fdimf.S: Likewise.
	* sysdeps/i386/i686/fpu/s_fdiml.S: Likewise.
	* sysdeps/powerpc/fpu/s_fdim.c: Likewise.
	* sysdeps/powerpc/fpu/s_fdimf.c: Likewise.
	* sysdeps/powerpc/powerpc32/fpu/s_fdim.c: Likewise.
	* sysdeps/powerpc/powerpc64/fpu/s_fdim.c: Likewise.
	* sysdeps/x86_64/fpu/s_fdiml.S: Likewise.
	* math/libm-test.inc (fdim_test_data): Expect errno setting on
	overflow.  Add sNaN tests.

2 files changed, 0 insertions, 56 deletions

diff --git a/sysdeps/powerpc/fpu/s_fdim.c b/sysdeps/powerpc/fpu/s_fdim.c
deleted file mode 100644
index 1d4b6d0665..0000000000
--- a/sysdeps/powerpc/fpu/s_fdim.c
+++ /dev/null
@@ -1,30 +0,0 @@
-/* Return positive difference between arguments.
-   Copyright (C) 1997-2016 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <http://www.gnu.org/licenses/>.  */
-
-#include <math.h>
-
-double
-__fdim (double x, double y)
-{
-  return x <= y ? 0 : x - y;
-}
-weak_alias (__fdim, fdim)
-#ifdef NO_LONG_DOUBLE
-strong_alias (__fdim, __fdiml)
-weak_alias (__fdim, fdiml)
-#endif
diff --git a/sysdeps/powerpc/fpu/s_fdimf.c b/sysdeps/powerpc/fpu/s_fdimf.c
deleted file mode 100644
index 8c645c413a..0000000000
--- a/sysdeps/powerpc/fpu/s_fdimf.c
+++ /dev/null
@@ -1,26 +0,0 @@
-/* Return positive difference between arguments.
-   Copyright (C) 1997-2016 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <http://www.gnu.org/licenses/>.  */
-
-#include <math.h>
-
-float
-__fdimf (float x, float y)
-{
-  return x <= y ? 0 : x - y;
-}
-weak_alias (__fdimf, fdimf)