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[Bug math/887] Math library function "logb" and "nextafter" inconsistent
- From: "rsa at us dot ibm.com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Mon, 26 Mar 2012 20:09:40 +0000
- Subject: [Bug math/887] Math library function "logb" and "nextafter" inconsistent
- Auto-submitted: auto-generated
- References: <bug-887-131@http.sourceware.org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=887
--- Comment #20 from Ryan S. Arnold <rsa at us dot ibm.com> 2012-03-26 20:09:40 UTC ---
Here's a more thorough patch which includes -frounding-math when building
s_logb.c and only tests on 'double'.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 3851855..df83a45 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -5000,6 +5000,41 @@ logb_test (void)
END (logb);
}
+static void
+logb_test_downward (void)
+{
+ int save_round_mode;
+ errno = 0;
+
+ FUNC(logb) (0);
+ if (errno == ENOSYS)
+ /* Function not implemented. */
+ return;
+
+ START (logb_downward);
+
+ save_round_mode = fegetround ();
+
+ if (!fesetround (FE_DOWNWARD))
+ {
+
+ /* IEEE 754-2008 says (section 5.3.3) that "logB(1) is +0.". Libm
+ * should not return -0 from logb in any rounding mode. PowerPC32 is
+ * known to fail with this test for power4 and earlier hardware due
+ * the instructions available for the logb computation at the POWER4
+ * and earlier ISA level. POWER4 uses an fsub in the calculation which
+ * propogates a negative sign in a downward rounding mode. */
+
+#if defined TEST_DOUBLE
+ /* BZ #887 .*/
+ TEST_f_f (logb, 1.000e+0, plus_zero);
+#endif /* TEST_DOUBLE */
+ }
+
+ fesetround (save_round_mode);
+
+ END (logb_downward);
+}
static void
lround_test (void)
@@ -7834,6 +7869,7 @@ main (int argc, char **argv)
log1p_test ();
log2_test ();
logb_test ();
+ logb_test_downward ();
modf_test ();
ilogb_test ();
scalb_test ();
diff --git a/sysdeps/powerpc/powerpc32/Makefile
b/sysdeps/powerpc/powerpc32/Makefile
index aa2d0b9..638e177 100644
--- a/sysdeps/powerpc/powerpc32/Makefile
+++ b/sysdeps/powerpc/powerpc32/Makefile
@@ -42,3 +42,9 @@ ifeq ($(subdir),elf)
# extra shared linker files to link only into dl-allobjs.so
sysdep-rtld-routines += dl-start
endif
+
+# BZ #887 logb for powerpc32 power4 ISA and earlier exhibits a negative sign
+# on zero from a downward round.
+ifeq ($(subdir),math)
+CFLAGS-s_logb.c += -frounding-math
+endif
--
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