Support __STDC_WANT_IEC_60559_BFP_EXT__ feature test macro.

This patch implements support for the __STDC_WANT_IEC_60559_BFP_EXT__
feature test macro from ISO/IEC 18661-1:2014, following the
__GLIBC_USE approach now used for __STDC_WANT_LIB_EXT2__.  For this
macro, the relevant consideration is whether it is defined or
undefined when an affected header is included (not what its value is
if defined, and not whether it's defined or undefined when any other
unaffected system header is included).

Currently this macro only affects the issignaling macro and the nextup
and nextdown functions (so they can be enabled by defining this macro,
not just by defining _GNU_SOURCE as previously).  Any further features
from this TS added in future would also be conditioned on this macro.

Tested for x86_64 and x86 (testsuite, and that installed stripped
shared libraries are unchanged by the patch).

	* bits/libc-header-start.h (__GLIBC_USE_IEC_60559_BFP_EXT): New
	macro.
	* include/features.h (__STDC_WANT_IEC_60559_BFP_EXT__): Document.
	* manual/arith.texi (issignaling): Document as ISO from TS
	18661-1:2014.
	(nextup): Likewise.
	(nextupf): Likewise.
	(nextupl): Likewise.
	(nextdown): Likewise.
	(nextdownf): Likewise.
	(nextdownl): Likewise.
	* manual/creature.texi (__STDC_WANT_IEC_60559_BFP_EXT__): Document
	macro.
	* math/math.h: Define
	__GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION and include
	<bits/libc-header-start.h> instead of including <features.h>.
	(issignaling): Define if [__GLIBC_USE (IEC_60559_BFP_EXT)], not
	[__USE_GNU].
	* math/bits/mathcalls.h (nextdown): Declare if
	[__GLIBC_USE (IEC_60559_BFP_EXT)], not [__USE_GNU].
	(nextup): Likewise.
	(__issignaling): Likewise.

8 files changed, 65 insertions, 16 deletions

diff --git a/ChangeLog b/ChangeLog
index 00fd7c107a..bd751f26d0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,28 @@
+2016-08-03  Joseph Myers  <joseph@codesourcery.com>
+
+	* bits/libc-header-start.h (__GLIBC_USE_IEC_60559_BFP_EXT): New
+	macro.
+	* include/features.h (__STDC_WANT_IEC_60559_BFP_EXT__): Document.
+	* manual/arith.texi (issignaling): Document as ISO from TS
+	18661-1:2014.
+	(nextup): Likewise.
+	(nextupf): Likewise.
+	(nextupl): Likewise.
+	(nextdown): Likewise.
+	(nextdownf): Likewise.
+	(nextdownl): Likewise.
+	* manual/creature.texi (__STDC_WANT_IEC_60559_BFP_EXT__): Document
+	macro.
+	* math/math.h: Define
+	__GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION and include
+	<bits/libc-header-start.h> instead of including <features.h>.
+	(issignaling): Define if [__GLIBC_USE (IEC_60559_BFP_EXT)], not
+	[__USE_GNU].
+	* math/bits/mathcalls.h (nextdown): Declare if
+	[__GLIBC_USE (IEC_60559_BFP_EXT)], not [__USE_GNU].
+	(nextup): Likewise.
+	(__issignaling): Likewise.
+
 2016-08-03  Paul E. Murphy  <murphyp@linux.vnet.ibm.com>
 
 	* s_ccoshf.c (__ccoshf): Remove FE_INVALID
diff --git a/NEWS b/NEWS
index d057c06b57..495bde01be 100644
--- a/NEWS
+++ b/NEWS
@@ -12,6 +12,11 @@ Version 2.25
   TR.  Note that not all functions from that TR are supported by the GNU C
   Library.
 
+* The feature test macro __STDC_WANT_IEC_60559_BFP_EXT__, from ISO/IEC TS
+  18661-1:2014, is supported to enable declarations of functions and macros
+  from that TS.  Note that most features from that TS are not supported by
+  the GNU C Library.
+
 Security related changes:
 
   [Add security related changes here]
diff --git a/bits/libc-header-start.h b/bits/libc-header-start.h
index c6663074a8..6a5850526c 100644
--- a/bits/libc-header-start.h
+++ b/bits/libc-header-start.h
@@ -41,3 +41,12 @@
 #else
 # define __GLIBC_USE_LIB_EXT2 0
 #endif
+
+/* ISO/IEC TS 18661-1:2014 defines the __STDC_WANT_IEC_60559_BFP_EXT__
+   macro.  */
+#undef __GLIBC_USE_IEC_60559_BFP_EXT
+#if defined __USE_GNU || defined __STDC_WANT_IEC_60559_BFP_EXT__
+# define __GLIBC_USE_IEC_60559_BFP_EXT 1
+#else
+# define __GLIBC_USE_IEC_60559_BFP_EXT 0
+#endif
diff --git a/include/features.h b/include/features.h
index 404014115a..f2cd148fa4 100644
--- a/include/features.h
+++ b/include/features.h
@@ -25,6 +25,7 @@
    _ISOC99_SOURCE	Extensions to ISO C89 from ISO C99.
    _ISOC11_SOURCE	Extensions to ISO C99 from ISO C11.
    __STDC_WANT_LIB_EXT2__ Extensions to ISO C99 from TR 27431-2:2010.
+   __STDC_WANT_IEC_60559_BFP_EXT__ Extensions to ISO C11 from TS 18661-1:2014.
    _POSIX_SOURCE	IEEE Std 1003.1.
    _POSIX_C_SOURCE	If ==1, like _POSIX_SOURCE; if >=2 add IEEE Std 1003.2;
 			if >=199309L, add IEEE Std 1003.1b-1993;
diff --git a/manual/arith.texi b/manual/arith.texi
index f54b1ec7df..3d8bdd8cad 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -397,12 +397,11 @@ to
 @end deftypefn
 
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefn {Macro} int issignaling (@emph{float-type} @var{x})
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
 This macro returns a nonzero value if @var{x} is a signaling NaN
-(sNaN).  It is based on draft TS 18661 and currently enabled as a GNU
-extension.
+(sNaN).  It is from TS 18661-1:2014.
 @end deftypefn
 
 Another set of floating-point classification functions was provided by
@@ -1703,13 +1702,13 @@ double}.
 @end deftypefun
 
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefun double nextup (double @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx float nextupf (float @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx {long double} nextupl (long double @var{x})
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
 The @code{nextup} function returns the next representable neighbor of @var{x}
@@ -1718,18 +1717,18 @@ subnormal number in the type of @var{x} the function returns @code{-0}.  If
 @math{@var{x} = @code{0}} the function returns the smallest positive subnormal
 number in the type of @var{x}.  If @var{x} is NaN, NaN is returned.
 If @var{x} is @math{+@infinity{}}, @math{+@infinity{}} is returned.
-@code{nextup} is based on TS 18661 and currently enabled as a GNU extension.
+@code{nextup} from TS 18661-1:2014.
 @code{nextup} never raises an exception except for signaling NaNs.
 @end deftypefun
 
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefun double nextdown (double @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx float nextdownf (float @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx {long double} nextdownl (long double @var{x})
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
 The @code{nextdown} function returns the next representable neighbor of @var{x}
@@ -1738,7 +1737,7 @@ subnormal number in the type of @var{x} the function returns @code{+0}.  If
 @math{@var{x} = @code{0}} the function returns the smallest negative subnormal
 number in the type of @var{x}.  If @var{x} is NaN, NaN is returned.
 If @var{x} is @math{-@infinity{}}, @math{-@infinity{}} is returned.
-@code{nextdown} is based on TS 18661 and currently enabled as a GNU extension.
+@code{nextdown} is from TS 18661-1:2014.
 @code{nextdown} never raises an exception except for signaling NaNs.
 @end deftypefun
 
diff --git a/manual/creature.texi b/manual/creature.texi
index 65c5928343..61b17ce22b 100644
--- a/manual/creature.texi
+++ b/manual/creature.texi
@@ -174,6 +174,15 @@ of the features from this TR are supported by @theglibc{}.
 @end defvr
 
 @comment (none)
+@comment ISO
+@defvr Macro __STDC_WANT_IEC_60559_BFP_EXT__
+If you define this macro, features from ISO/IEC TS 18661-1:2014
+(Floating-point extensions for C: Binary floating-point arithmetic)
+are enabled.  Only some of the features from this TS are supported by
+@theglibc{}.
+@end defvr
+
+@comment (none)
 @comment GNU
 @defvr Macro _GNU_SOURCE
 If you define this macro, everything is included: @w{ISO C89}, @w{ISO
diff --git a/math/bits/mathcalls.h b/math/bits/mathcalls.h
index e2cf49f627..e1c0521ae8 100644
--- a/math/bits/mathcalls.h
+++ b/math/bits/mathcalls.h
@@ -294,7 +294,7 @@ __MATHCALLX (nextafter,, (_Mdouble_ __x, _Mdouble_ __y), (__const__));
 __MATHCALLX (nexttoward,, (_Mdouble_ __x, long double __y), (__const__));
 # endif
 
-#ifdef __USE_GNU
+#if __GLIBC_USE (IEC_60559_BFP_EXT)
 /* Return X - epsilon.  */
 __MATHCALL (nextdown,, (_Mdouble_ __x));
 /* Return X + epsilon.  */
@@ -377,7 +377,7 @@ __MATHCALL (fma,, (_Mdouble_ __x, _Mdouble_ __y, _Mdouble_ __z));
 __END_NAMESPACE_C99
 #endif
 
-#ifdef __USE_GNU
+#if __GLIBC_USE (IEC_60559_BFP_EXT)
 /* Test for signaling NaN.  */
 __MATHDECL_1 (int, __issignaling,, (_Mdouble_ __value))
      __attribute__ ((__const__));
diff --git a/math/math.h b/math/math.h
index 4724b10b6f..ff9d70adf5 100644
--- a/math/math.h
+++ b/math/math.h
@@ -23,7 +23,8 @@
 #ifndef	_MATH_H
 #define	_MATH_H	1
 
-#include <features.h>
+#define __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
+#include <bits/libc-header-start.h>
 
 __BEGIN_DECLS
 
@@ -328,7 +329,7 @@ enum
 
 #endif /* Use ISO C99.  */
 
-#ifdef __USE_GNU
+#if __GLIBC_USE (IEC_60559_BFP_EXT)
 /* Return nonzero value if X is a signaling NaN.  */
 # ifdef __NO_LONG_DOUBLE_MATH
 #  define issignaling(x) \
@@ -340,7 +341,7 @@ enum
       : sizeof (x) == sizeof (double)					      \
       ? __issignaling (x) : __issignalingl (x))
 # endif
-#endif /* Use GNU.  */
+#endif /* Use IEC_60559_BFP_EXT.  */
 
 #ifdef	__USE_MISC
 /* Support for various different standard error handling behaviors.  */