Add issubnormal.

TS 18661-1 adds an issubnormal classification macro to <math.h>.  This
patch implements it for glibc.  There are no new underlying functions
in libm because the implementation uses fpclassify; any optimizations
for this macro should be done through adding __builtin_subnormal in
GCC and using it in the header for suitable GCC versions, not through
adding other optimized inline or out-of-line versions to glibc.

The intended structure of the NEWS entry for <math.h> features from TS
18661-1 is like:

* New <math.h> features are added from TS 18661-1:2014:

  - Nearest integer functions: roundeven, roundevenf, roundevenl.

  - Comparison macros: iseqsig.

  - Classification macros: iscanonical, issubnormal, iszero.

(that is, following the grouping of interfaces in TS 18661-1:2014,
with any group where any interfaces are new in glibc 2.25 being listed
like that).

Tested for x86_64 and x86.

	* math/math.h [__GLIBC_USE (IEC_60559_BFP_EXT)] (issubnormal): New
	macro.
	* math/libm-test.inc (issubnormal_test_data): New array.
	(issubnormal_test): New function.
	* manual/arith.texi (Floating Point Classes): Document
	issubnormal.
	* manual/libm-err-tab.pl: Update comment on interfaces without
	ulps tabulated.

1 files changed, 8 insertions, 0 deletions

diff --git a/manual/arith.texi b/manual/arith.texi
index dc3c367d49..bfa236a50e 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -406,6 +406,14 @@ This macro returns a nonzero value if @var{x} is a signaling NaN
 (sNaN).  It is from TS 18661-1:2014.
 @end deftypefn
 
+@comment math.h
+@comment ISO
+@deftypefn {Macro} int issubnormal (@emph{float-type} @var{x})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This macro returns a nonzero value if @var{x} is subnormal.  It is
+from TS 18661-1:2014.
+@end deftypefn
+
 Another set of floating-point classification functions was provided by
 BSD.  @Theglibc{} also supports these functions; however, we
 recommend that you use the ISO C99 macros in new code.  Those are standard