--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2008-03-30  Eric Blake  <ebb9@byu.net>
 
+	Test signbit behavior on zeros.
+	* tests/test-signbit.c (test_signbitf): Add tests for zero.
+	(test_signbitd, test_signbitl): Likewise.
+
 	More strtod touchups.
 	* tests/test-strtod.c (main): Ignore tests for signbit on NaN, and
 	sign of negative underflow, for now.  Use .5, not .1.

--- a/tests/test-signbit.c
+++ b/tests/test-signbit.c
@@ -1,5 +1,5 @@
 /* Test of signbit() substitute.
-   Copyright (C) 2007 Free Software Foundation, Inc.
+   Copyright (C) 2007, 2008 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -49,6 +49,12 @@
   ASSERT (signbit (-2.718f));
   ASSERT (signbit (-2.718e30f));
   ASSERT (signbit (-2.718e-30f));
+  /* Zeros.  */
+  ASSERT (!signbit (0.0f));
+  if (1.0f / -zerof < 0)
+    ASSERT (signbit (-0.0f));
+  else
+    ASSERT (!signbit (-0.0f));
   /* Infinite values.  */
   ASSERT (!signbit (1.0f / 0.0f));
   ASSERT (signbit (-1.0f / 0.0f));
@@ -88,6 +94,12 @@
   ASSERT (signbit (-2.718));
   ASSERT (signbit (-2.718e30));
   ASSERT (signbit (-2.718e-30));
+  /* Zeros.  */
+  ASSERT (!signbit (0.0));
+  if (1.0 / -zerod < 0)
+    ASSERT (signbit (-0.0));
+  else
+    ASSERT (!signbit (-0.0));
   /* Infinite values.  */
   ASSERT (!signbit (1.0 / 0.0));
   ASSERT (signbit (-1.0 / 0.0));
@@ -125,6 +137,12 @@
   ASSERT (signbit (-2.718L));
   ASSERT (signbit (-2.718e30L));
   ASSERT (signbit (-2.718e-30L));
+  /* Zeros.  */
+  ASSERT (!signbit (0.0L));
+  if (1.0L / -zerol < 0)
+    ASSERT (signbit (-0.0L));
+  else
+    ASSERT (!signbit (-0.0L));
   /* Infinite values.  */
   ASSERT (!signbit (1.0L / 0.0L));
   ASSERT (signbit (-1.0L / 0.0L));