4 files changed, 92 insertions, 1 deletions
diff --git a/sysdeps/ieee754/ldbl-128/Makeconfig b/sysdeps/ieee754/ldbl-128/Makeconfig
new file mode 100644
index 0000000000..1f8e2562f0
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128/Makeconfig
@@ -0,0 +1,3 @@
+# Include this earlier so it can be used earlier in Makefiles,
+# and sysdep/ makefiles.
+float128-alias-fcts = yes
diff --git a/sysdeps/ieee754/ldbl-128/bits/floatn.h b/sysdeps/ieee754/ldbl-128/bits/floatn.h
new file mode 100644
index 0000000000..5c87366aef
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128/bits/floatn.h
@@ -0,0 +1,80 @@
+/* Macros to control TS 18661-3 glibc features on ldbl-128 platforms.
+   Copyright (C) 2017 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/>.  */
+
+#ifndef _BITS_FLOATN_H
+#define _BITS_FLOATN_H
+
+#include <features.h>
+#include <bits/long-double.h>
+
+/* Defined to 1 if the current compiler invocation provides a
+   floating-point type with the IEEE 754 binary128 format, and this
+   glibc includes corresponding *f128 interfaces for it.  */
+#ifndef __NO_LONG_DOUBLE_MATH
+# define __HAVE_FLOAT128 1
+#else
+/* glibc does not support _Float128 for platforms where long double is
+   normally binary128 when building with long double as binary64.
+   GCC's default for supported scalar modes does not support it either
+   in that case.  */
+# define __HAVE_FLOAT128 0
+#endif
+
+/* Defined to 1 if __HAVE_FLOAT128 is 1 and the type is ABI-distinct
+   from the default float, double and long double types in this glibc.  */
+#define __HAVE_DISTINCT_FLOAT128 0
+
+/* Defined to concatenate the literal suffix to be used with _Float128
+   types, if __HAVE_FLOAT128 is 1. */
+#if __HAVE_FLOAT128
+# if !__GNUC_PREREQ (7, 0) || defined __cplusplus
+/* The literal suffix f128 exists only since GCC 7.0.  */
+#  define __f128(x) x##l
+# else
+#  define __f128(x) x##f128
+# endif
+#endif
+
+/* Defined to a complex binary128 type if __HAVE_FLOAT128 is 1.  */
+#if __HAVE_FLOAT128
+# if !__GNUC_PREREQ (7, 0) || defined __cplusplus
+#  define __CFLOAT128 _Complex long double
+# else
+#  define __CFLOAT128 _Complex _Float128
+# endif
+#endif
+
+/* The remaining of this file provides support for older compilers.  */
+#if __HAVE_FLOAT128
+
+/* The type _Float128 exists only since GCC 7.0.  */
+# if !__GNUC_PREREQ (7, 0) || defined __cplusplus
+typedef long double _Float128;
+# endif
+
+/* Various built-in functions do not exist before GCC 7.0.  */
+# if !__GNUC_PREREQ (7, 0)
+#  define __builtin_huge_valf128() (__builtin_huge_vall ())
+#  define __builtin_inff128() (__builtin_infl ())
+#  define __builtin_nanf128(x) (__builtin_nanl (x))
+#  define __builtin_nansf128(x) (__builtin_nansl (x))
+# endif
+
+#endif
+
+#endif /* _BITS_FLOATN_H */
diff --git a/sysdeps/ieee754/ldbl-128/float128-abi.h b/sysdeps/ieee754/ldbl-128/float128-abi.h
new file mode 100644
index 0000000000..3077ffc7fe
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128/float128-abi.h
@@ -0,0 +1,2 @@
+/* ABI version for _Float128 ABI introduction.  */
+#define FLOAT128_VERSION GLIBC_2.27
diff --git a/sysdeps/ieee754/ldbl-opt/libm-alias-ldouble.h b/sysdeps/ieee754/ldbl-opt/libm-alias-ldouble.h
index 291a5f56cb..ad31f69f1a 100644
--- a/sysdeps/ieee754/ldbl-opt/libm-alias-ldouble.h
+++ b/sysdeps/ieee754/ldbl-opt/libm-alias-ldouble.h
@@ -19,6 +19,7 @@
 #ifndef _LIBM_ALIAS_LDOUBLE_H
 #define _LIBM_ALIAS_LDOUBLE_H
 
+#include <bits/floatn.h>
 #include <math_ldbl_opt.h>
 #include <ldbl-compat-choose.h>
 
@@ -26,7 +27,12 @@
    that has internal name FROM ## l ## R and public names TO ## suffix
    ## R for each suffix of a supported _FloatN / _FloatNx
    floating-point type with the same format as long double.  */
-#define libm_alias_ldouble_other_r(from, to, r)
+#if __HAVE_FLOAT128 && !__HAVE_DISTINCT_FLOAT128
+# define libm_alias_ldouble_other_r(from, to, r)	\
+  weak_alias (from ## l ## r, to ## f128 ## r)
+#else
+# define libm_alias_ldouble_other_r(from, to, r)
+#endif
 
 /* Likewise, but without the R suffix.  */
 #define libm_alias_ldouble_other(from, to)	\