ldbl-128ibm-compat: Provide nexttoward functions

The functions in the nexttoward family are special, in the sense that
they always have a long double argument, regardless of their suffix
(i.e.: nexttowardf and nexttoward have a long double argument, besides
the float and double arguments).

On top of that, they are also special because nexttoward functions are
not part of the _FloatN API, hence __nexttowardf128 do not exist.

This patch adds 4 new function implementations for the new long double
format:

  __nexttoward_to_ieee128
  __nexttowardf_to_ieee128
  __nexttowardieee128 (as an alias to __nextafterieee128)

Likewise, rename "long double" "_Float128" in shared ldbl-128
files to ensure correct type is used irrespective of ABI
switches.

Thank you to those who helped out with this patch:

Co-Authored-By: Tulio Magno Quites Machado Filho  <tuliom@linux.ibm.com>

3 files changed, 61 insertions, 0 deletions

diff --git a/sysdeps/ieee754/ldbl-128ibm-compat/Versions b/sysdeps/ieee754/ldbl-128ibm-compat/Versions
index 7224e1ddc7..07e6a5b08a 100644
--- a/sysdeps/ieee754/ldbl-128ibm-compat/Versions
+++ b/sysdeps/ieee754/ldbl-128ibm-compat/Versions
@@ -91,6 +91,9 @@ libm {
     __nearbyintieee128;
     __nextafterieee128;
     __nextdownieee128;
+    __nexttowardf_to_ieee128;
+    __nexttowardieee128;
+    __nexttoward_to_ieee128;
     __nextupieee128;
     __powieee128;
     __remainderieee128;
diff --git a/sysdeps/ieee754/ldbl-128ibm-compat/s_nextafterf128.c b/sysdeps/ieee754/ldbl-128ibm-compat/s_nextafterf128.c
new file mode 100644
index 0000000000..cc30ae02d7
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128ibm-compat/s_nextafterf128.c
@@ -0,0 +1,20 @@
+/* Provide nexttowardl and nextafterl implementations for IEEE long double.
+   Copyright (C) 2020 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 "../float128/s_nextafterf128.c"
+
+strong_alias (__nextafterieee128, __nexttowardieee128)
diff --git a/sysdeps/ieee754/ldbl-128ibm-compat/s_nexttowardf128.c b/sysdeps/ieee754/ldbl-128ibm-compat/s_nexttowardf128.c
new file mode 100644
index 0000000000..0b4204cf64
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128ibm-compat/s_nexttowardf128.c
@@ -0,0 +1,38 @@
+/* Provide nexttoward[|f] implementations for IEEE long double.
+   Copyright (C) 2020 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 <float128_private.h>
+
+/* Build nexttoward functions with binary128 format.  */
+#undef weak_alias
+#define weak_alias(from, to)
+#undef libm_alias_ldouble
+#define libm_alias_ldouble(from, to)
+#undef __nexttoward
+#define __nexttoward __nexttoward_to_ieee128
+#include <sysdeps/ieee754/ldbl-128/s_nexttoward.c>
+
+#undef weak_alias
+#define weak_alias(from, to)
+#undef libm_alias_ldouble
+#define libm_alias_ldouble(from, to)
+#undef __nexttowardf
+#define __nexttowardf __nexttowardf_to_ieee128
+#include <sysdeps/ieee754/ldbl-128/s_nexttowardf.c>
+
+#include <libm-alias-ldouble.h>