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.

2 files changed, 30 insertions, 1 deletions

diff --git a/math/libm-test.inc b/math/libm-test.inc
index e4fcb5a..385ec5c 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -46,7 +46,7 @@
    cbrt, ceil, copysign, cos, cosh, drem, erf, erfc, exp, exp10, exp2, expm1,
    fabs, fdim, finite, floor, fma, fmax, fmin, fmod, fpclassify,
    frexp, gamma, hypot,
-   ilogb, isfinite, isinf, isnan, isnormal, issignaling,
+   ilogb, isfinite, isinf, isnan, isnormal, issignaling, issubnormal,
    isless, islessequal, isgreater, isgreaterequal, islessgreater, isunordered,
    j0, j1, jn,
    ldexp, lgamma, log, log10, log1p, log2, logb,
@@ -8587,6 +8587,31 @@ issignaling_test (void)
   ALL_RM_TEST (issignaling, 1, issignaling_test_data, RUN_TEST_LOOP_f_b_tg, END);
 }
 
+static const struct test_f_i_data issubnormal_test_data[] =
+  {
+    TEST_f_b (issubnormal, 0, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, minus_zero, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, 10, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, min_subnorm_value, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -min_subnorm_value, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, min_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -min_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, max_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -max_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, plus_infty, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, minus_infty, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, qnan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -qnan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, snan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -snan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+  };
+
+static void
+issubnormal_test (void)
+{
+  ALL_RM_TEST (issubnormal, 1, issubnormal_test_data, RUN_TEST_LOOP_f_b_tg, END);
+}
+
 static const struct test_ff_i_data isunordered_test_data[] =
   {
     TEST_ff_i (isunordered, minus_zero, minus_zero, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
@@ -12668,6 +12693,7 @@ main (int argc, char **argv)
   isnan_test ();
   isnormal_test ();
   issignaling_test ();
+  issubnormal_test ();
   signbit_test ();
 
   /* Trigonometric functions:  */
diff --git a/math/math.h b/math/math.h
index 2f77dee..064cc56 100644
--- a/math/math.h
+++ b/math/math.h
@@ -328,6 +328,9 @@ enum
       : sizeof (x) == sizeof (double)					      \
       ? __issignaling (x) : __issignalingl (x))
 # endif
+
+/* Return nonzero value if X is subnormal.  */
+# define issubnormal(x) (fpclassify (x) == FP_SUBNORMAL)
 #endif /* Use IEC_60559_BFP_EXT.  */
 
 #ifdef	__USE_MISC