Do not call __nan in scalb functions.

When libm functions return a NaN: if it is for NaN input, it should be
computed from that input (e.g. adding it to itself), so that payloads
are propagated and signaling NaNs quieted, while if it is for non-NaN
input, it should be produced by a computation such as
(x - x) / (x - x), which raises "invalid" at the same time as
producing an appropriate NaN, so avoiding any need for a call to
feraiseexcept.

Various libm functions, however, call __nan ("") (or __nanf or __nanl)
to determine the NaN to return, together with using feraiseexcept
(FE_INVALID) to raise the exception.  sysdeps/generic/math_private.h
has an optimization for those functions with constant "" argument so
this doesn't actually involve a call to the __nan function, but it is
still not the preferred approach for producing NaNs.  (The optimized
code also always uses the NAN macro, i.e. produces a default NaN for
float converted to whatever the target type is, and on some
architectures that may not be the same as the preferred default NaN
for double or long double.)

This patch fixes the scalb functions to use the conventional method of
generating NaNs and raising "invalid" with an appropriate
computation.  (Most instances of this issue are in the complex
functions, where it can more readily be fixed once they have been made
type-generic and so only a third as many places need fixing.  Some of
the complex functions use __nan ("") + __nan (""), where the addition
serves no purpose whatsoever.)

Tested for x86_64 and x86.

	* math/e_scalb.c: Do not include <fenv.h>.
	(invalid_fn): Do calculation resulting in NaN instead of raising
	FE_INVALID and returning a NaN explicitly.
	* math/e_scalbf.c: Do not include <fenv.h>.
	(invalid_fn): Do calculation resulting in NaN instead of raising
	FE_INVALID and returning a NaN explicitly.
	* math/e_scalbl.c: Do not include <fenv.h>.
	(invalid_fn): Do calculation resulting in NaN instead of raising
	FE_INVALID and returning a NaN explicitly.

diff --git a/ChangeLog b/ChangeLog
index e2e53175ea9a4d40e9612002aad088bc2676f502..1e63a386fe4c56564615be5279847bdf8fd63d64 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2016-08-04  Joseph Myers  <joseph@codesourcery.com>
+
+       * math/e_scalb.c: Do not include <fenv.h>.
+       (invalid_fn): Do calculation resulting in NaN instead of raising
+       FE_INVALID and returning a NaN explicitly.
+       * math/e_scalbf.c: Do not include <fenv.h>.
+       (invalid_fn): Do calculation resulting in NaN instead of raising
+       FE_INVALID and returning a NaN explicitly.
+       * math/e_scalbl.c: Do not include <fenv.h>.
+       (invalid_fn): Do calculation resulting in NaN instead of raising
+       FE_INVALID and returning a NaN explicitly.
+
 2016-08-04  Carlos O'Donell  <carlos@redhat.com>
 
        * po/de.po: Updated from Translation Project.

diff --git a/math/e_scalb.c b/math/e_scalb.c
index 7f61ce045575c7f50ece32d7242fe3e58b71bda0..692f105d7f631c04d4811ac4a778d42de583c51c 100644 (file)
--- a/math/e_scalb.c
+++ b/math/e_scalb.c
@@ -16,7 +16,6 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <fenv.h>
 #include <math.h>
 #include <math_private.h>
 
@@ -26,10 +25,7 @@ __attribute__ ((noinline))
 invalid_fn (double x, double fn)
 {
   if (__rint (fn) != fn)
-    {
-      __feraiseexcept (FE_INVALID);
-      return __nan ("");
-    }
+    return (fn - fn) / (fn - fn);
   else if (fn > 65000.0)
     return __scalbn (x, 65000);
   else

diff --git a/math/e_scalbf.c b/math/e_scalbf.c
index 7377f6e1e84f80994506b77df9181130ab964ba7..8df86f4bb86c0b4aee4ea0b993307d405f487e86 100644 (file)
--- a/math/e_scalbf.c
+++ b/math/e_scalbf.c
@@ -16,7 +16,6 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <fenv.h>
 #include <math.h>
 #include <math_private.h>
 
@@ -26,10 +25,7 @@ __attribute__ ((noinline))
 invalid_fn (float x, float fn)
 {
   if (__rintf (fn) != fn)
-    {
-      feraiseexcept (FE_INVALID);
-      return __nan ("");
-    }
+    return (fn - fn) / (fn - fn);
   else if (fn > 65000.0f)
     return __scalbnf (x, 65000);
   else

diff --git a/math/e_scalbl.c b/math/e_scalbl.c
index 53e9ca22f1612753f17e021280a4d710992aa3ac..02956ac9e6bd0412c45b93d2eadfb91d9965ab2a 100644 (file)
--- a/math/e_scalbl.c
+++ b/math/e_scalbl.c
@@ -16,7 +16,6 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <fenv.h>
 #include <math.h>
 #include <math_private.h>
 
@@ -26,10 +25,7 @@ __attribute__ ((noinline))
 invalid_fn (long double x, long double fn)
 {
   if (__rintl (fn) != fn)
-    {
-      feraiseexcept (FE_INVALID);
-      return __nan ("");
-    }
+    return (fn - fn) / (fn - fn);
   else if (fn > 65000.0L)
     return __scalbnl (x, 65000);
   else