--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2012-04-01  Bruno Haible  <bruno@clisp.org>
 
+	log10f-ieee: Work around test failure on NetBSD 5.1.
+	* m4/log10f-ieee.m4: New file.
+	* m4/log10f.m4 (gl_FUNC_LOG10F): If gl_FUNC_LOG10F_IEEE is present,
+	test whether log10f works with a negative argument. Replace it if not.
+	* lib/log10f.c (log10f): For negative arguments, return NaN.
+	* modules/log10f-ieee (Files): Add m4/log10f-ieee.m4.
+	(configure.ac): Invoke gl_FUNC_LOG10F_IEEE.
+	* doc/posix-functions/log10f.texi: Mention the log10f-ieee module.
+
 	log10f-ieee: Work around test failure on Solaris 9.
 	* modules/log10f-ieee (Depends-on): Add log10-ieee.
 	(configure.ac): Require gl_FUNC_LOG10F.

--- a/doc/posix-functions/log10f.texi
+++ b/doc/posix-functions/log10f.texi
@@ -4,9 +4,9 @@
 
 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/log10f.html}
 
-Gnulib module: log10f
+Gnulib module: log10f or log10f-ieee
 
-Portability problems fixed by Gnulib:
+Portability problems fixed by either Gnulib module @code{log10f} or @code{log10f-ieee}:
 @itemize
 @item
 This function is missing on some platforms:
@@ -19,6 +19,13 @@
 OSF/1 5.1.
 @end itemize
 
+Portability problems fixed by Gnulib module @code{log10f-ieee}:
+@itemize
+@item
+This function returns a wrong value for a negative argument on some platforms:
+NetBSD 5.1.
+@end itemize
+
 Portability problems not fixed by Gnulib:
 @itemize
 @end itemize

--- a/lib/log10f.c
+++ b/lib/log10f.c
@@ -24,10 +24,17 @@
 #undef log10f
 {
 #if HAVE_LOG10F
-  /* Work around the OSF/1 5.1 bug.  */
-  if (x == 0.0f)
-    /* Return -Infinity.  */
-    return -1.0f / 0.0f;
+  if (x <= 0.0f)
+    {
+      /* Work around the OSF/1 5.1 bug.  */
+      if (x == 0.0f)
+        /* Return -Infinity.  */
+        return -1.0f / 0.0f;
+      /* Work around the NetBSD 5.1 bug.  */
+      else /* x < 0.0 */
+        /* Return NaN.  */
+        return 0.0f / 0.0f;
+    }
   return log10f (x);
 #else
   return (float) log10 ((double) x);

new file mode 100644
--- /dev/null
+++ b/m4/log10f-ieee.m4
@@ -0,0 +1,15 @@
+# log10f-ieee.m4 serial 1
+dnl Copyright (C) 2012 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl This macro is in a separate file (not in remainder.m4 and not inlined in the
+dnl module description), so that gl_FUNC_LOG10F can test whether 'aclocal' has
+dnl found uses of this macro.
+
+AC_DEFUN([gl_FUNC_LOG10F_IEEE],
+[
+  m4_divert_text([INIT_PREPARE], [gl_log10f_required=ieee])
+  AC_REQUIRE([gl_FUNC_LOG10F])
+])

--- a/m4/log10f.m4
+++ b/m4/log10f.m4
@@ -1,4 +1,4 @@
-# log10f.m4 serial 3
+# log10f.m4 serial 4
 dnl Copyright (C) 2011-2012 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -6,6 +6,7 @@
 
 AC_DEFUN([gl_FUNC_LOG10F],
 [
+  m4_divert_text([DEFAULTS], [gl_log10f_required=plain])
   AC_REQUIRE([gl_MATH_H_DEFAULTS])
   AC_REQUIRE([gl_FUNC_LOG10])
 
@@ -29,6 +30,51 @@
       *yes) ;;
       *) REPLACE_LOG10F=1 ;;
     esac
+
+    m4_ifdef([gl_FUNC_LOG10F_IEEE], [
+      if test $gl_log10f_required = ieee && test $REPLACE_LOG10F = 0; then
+        AC_CACHE_CHECK([whether log10f works according to ISO C 99 with IEC 60559],
+          [gl_cv_func_log10f_ieee],
+          [
+            save_LIBS="$LIBS"
+            LIBS="$LIBS $LOGF_LIBM"
+            AC_RUN_IFELSE(
+              [AC_LANG_SOURCE([[
+#ifndef __NO_MATH_INLINES
+# define __NO_MATH_INLINES 1 /* for glibc */
+#endif
+#include <math.h>
+/* Compare two numbers with ==.
+   This is a separate function because IRIX 6.5 "cc -O" miscompiles an
+   'x == x' test.  */
+static int
+numeric_equal (float x, float y)
+{
+  return x == y;
+}
+static float dummy (float x) { return 0; }
+int main (int argc, char *argv[])
+{
+  float (*my_log10f) (float) = argc ? log10f : dummy;
+  /* Test log10f(negative).
+     This test fails on NetBSD 5.1.  */
+  float y = my_log10f (-1.0f);
+  if (numeric_equal (y, y))
+    return 1;
+  return 0;
+}
+              ]])],
+              [gl_cv_func_log10f_ieee=yes],
+              [gl_cv_func_log10f_ieee=no],
+              [gl_cv_func_log10f_ieee="guessing no"])
+            LIBS="$save_LIBS"
+          ])
+        case "$gl_cv_func_log10f_ieee" in
+          *yes) ;;
+          *) REPLACE_LOG10F=1 ;;
+        esac
+      fi
+    ])
   else
     HAVE_LOG10F=0
   fi

--- a/modules/log10f-ieee
+++ b/modules/log10f-ieee
@@ -2,6 +2,7 @@
 log10f() function according to ISO C 99 with IEC 60559.
 
 Files:
+m4/log10f-ieee.m4
 
 Depends-on:
 log10f
@@ -9,7 +10,7 @@
 log10-ieee      [test $HAVE_LOG10F = 0 || test $REPLACE_LOG10F = 1]
 
 configure.ac:
-AC_REQUIRE([gl_FUNC_LOG10F])
+gl_FUNC_LOG10F_IEEE
 
 Makefile.am: