Add narrowing fma functions

This patch adds the narrowing fused multiply-add functions from TS
18661-1 / TS 18661-3 / C2X to glibc's libm: ffma, ffmal, dfmal,
f32fmaf64, f32fmaf32x, f32xfmaf64 for all configurations; f32fmaf64x,
f32fmaf128, f64fmaf64x, f64fmaf128, f32xfmaf64x, f32xfmaf128,
f64xfmaf128 for configurations with _Float64x and _Float128;
__f32fmaieee128 and __f64fmaieee128 aliases in the powerpc64le case
(for calls to ffmal and dfmal when long double is IEEE binary128).
Corresponding tgmath.h macro support is also added.

The changes are mostly similar to those for the other narrowing
functions previously added, especially that for sqrt, so the
description of those generally applies to this patch as well.  As with
sqrt, I reused the same test inputs in auto-libm-test-in as for
non-narrowing fma rather than adding extra or separate inputs for
narrowing fma.  The tests in libm-test-narrow-fma.inc also follow
those for non-narrowing fma.

The non-narrowing fma has a known bug (bug 6801) that it does not set
errno on errors (overflow, underflow, Inf * 0, Inf - Inf).  Rather
than fixing this or having narrowing fma check for errors when
non-narrowing does not (complicating the cases when narrowing fma can
otherwise be an alias for a non-narrowing function), this patch does
not attempt to check for errors from narrowing fma and set errno; the
CHECK_NARROW_FMA macro is still present, but as a placeholder that
does nothing, and this missing errno setting is considered to be
covered by the existing bug rather than needing a separate open bug.
missing-errno annotations are duly added to many of the
auto-libm-test-in test inputs for fma.

This completes adding all the new functions from TS 18661-1 to glibc,
so will be followed by corresponding stdc-predef.h changes to define
__STDC_IEC_60559_BFP__ and __STDC_IEC_60559_COMPLEX__, as the support
for TS 18661-1 will be at a similar level to that for C standard
floating-point facilities up to C11 (pragmas not implemented, but
library functions done).  (There are still further changes to be done
to implement changes to the types of fromfp functions from N2548.)

Tested as followed: natively with the full glibc testsuite for x86_64
(GCC 11, 7, 6) and x86 (GCC 11); with build-many-glibcs.py with GCC
11, 7 and 6; cross testing of math/ tests for powerpc64le, powerpc32
hard float, mips64 (all three ABIs, both hard and soft float).  The
different GCC versions are to cover the different cases in tgmath.h
and tgmath.h tests properly (GCC 6 has _Float* only as typedefs in
glibc headers, GCC 7 has proper _Float* support, GCC 8 adds
__builtin_tgmath).

3 files changed, 42 insertions, 0 deletions

diff --git a/sysdeps/ieee754/dbl-64/s_f32xfmaf64.c b/sysdeps/ieee754/dbl-64/s_f32xfmaf64.c
new file mode 100644
index 0000000000..8ee50d9f4a
--- /dev/null
+++ b/sysdeps/ieee754/dbl-64/s_f32xfmaf64.c
@@ -0,0 +1 @@
+/* Defined as an alias of fma.  */
diff --git a/sysdeps/ieee754/dbl-64/s_ffma.c b/sysdeps/ieee754/dbl-64/s_ffma.c
new file mode 100644
index 0000000000..6af70d6368
--- /dev/null
+++ b/sysdeps/ieee754/dbl-64/s_ffma.c
@@ -0,0 +1,35 @@
+/* Fused multiply-add of double value, narrowing the result to float.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+#define f32fmaf64 __hide_f32fmaf64
+#define f32fmaf32x __hide_f32fmaf32x
+#define ffmal __hide_ffmal
+#include <math.h>
+#undef f32fmaf64
+#undef f32fmaf32x
+#undef ffmal
+
+#include <math-narrow.h>
+
+float
+__ffma (double x, double y, double z)
+{
+  NARROW_FMA_ROUND_TO_ODD (x, y, z, float, union ieee754_double, , mantissa1,
+			   false);
+}
+libm_alias_float_double (fma)
diff --git a/sysdeps/ieee754/dbl-64/s_fma.c b/sysdeps/ieee754/dbl-64/s_fma.c
index aa4336387a..87e59033e4 100644
--- a/sysdeps/ieee754/dbl-64/s_fma.c
+++ b/sysdeps/ieee754/dbl-64/s_fma.c
@@ -18,12 +18,17 @@
 
 #define NO_MATH_REDIRECT
 #include <float.h>
+#define dfmal __hide_dfmal
+#define f32xfmaf64 __hide_f32xfmaf64
 #include <math.h>
+#undef dfmal
+#undef f32xfmaf64
 #include <fenv.h>
 #include <ieee754.h>
 #include <math-barriers.h>
 #include <fenv_private.h>
 #include <libm-alias-double.h>
+#include <math-narrow-alias.h>
 #include <tininess.h>
 #include <math-use-builtins.h>
 
@@ -301,4 +306,5 @@ __fma (double x, double y, double z)
 }
 #ifndef __fma
 libm_alias_double (__fma, fma)
+libm_alias_double_narrow (__fma, fma)
 #endif