Add fmaximum, fminimum functions

C2X adds new <math.h> functions for floating-point maximum and
minimum, corresponding to the new operations that were added in IEEE
754-2019 because of concerns about the old operations not being
associative in the presence of signaling NaNs.  fmaximum and fminimum
handle NaNs like most <math.h> functions (any NaN argument means the
result is a quiet NaN).  fmaximum_num and fminimum_num handle both
quiet and signaling NaNs the way fmax and fmin handle quiet NaNs (if
one argument is a number and the other is a NaN, return the number),
but still raise "invalid" for a signaling NaN argument, making them
exceptions to the normal rule that a function with a floating-point
result raising "invalid" also returns a quiet NaN.  fmaximum_mag,
fminimum_mag, fmaximum_mag_num and fminimum_mag_num are corresponding
functions returning the argument with greatest or least absolute
value.  All these functions also treat +0 as greater than -0.  There
are also corresponding <tgmath.h> type-generic macros.

Add these functions to glibc.  The implementations use type-generic
templates based on those for fmax, fmin, fmaxmag and fminmag, and test
inputs are based on those for those functions with appropriate
adjustments to the expected results.  The RISC-V maintainers might
wish to add optimized versions of fmaximum_num and fminimum_num (for
float and double), since RISC-V (F extension version 2.2 and later)
provides instructions corresponding to those functions - though it
might be at least as useful to add architecture-independent built-in
functions to GCC and teach the RISC-V back end to expand those
functions inline, which is what you generally want for functions that
can be implemented with a single instruction.

Tested for x86_64 and x86, and with build-many-glibcs.py.

1 files changed, 35 insertions, 0 deletions

diff --git a/math/s_fmaximum_mag_num_template.c b/math/s_fmaximum_mag_num_template.c
new file mode 100644
index 0000000000..5c9cef21fd
--- /dev/null
+++ b/math/s_fmaximum_mag_num_template.c
@@ -0,0 +1,35 @@
+/* Return number with maximum magnitude.
+   Copyright (C) 2016-2021 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/>.  */
+
+#include <math.h>
+
+FLOAT
+M_DECL_FUNC (__fmaximum_mag_num) (FLOAT x, FLOAT y)
+{
+  FLOAT ax = M_FABS (x);
+  FLOAT ay = M_FABS (y);
+  if (isgreater (ax, ay))
+    return x;
+  else if (isless (ax, ay))
+    return y;
+  else if (ax == ay)
+    return (M_COPYSIGN (1, x) >= M_COPYSIGN (1, y) ? x : y);
+  else
+    return isnan (y) ? (isnan (x) ? x + y : x) : y;
+}
+declare_mgen_alias (__fmaximum_mag_num, fmaximum_mag_num);