--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2012-04-01  Bruno Haible  <bruno@clisp.org>
+
+	log10: Work around OSF/1 5.1 bug.
+	* lib/math.in.h (log10): New declaration.
+	* lib/log10.c: New file.
+	* m4/log10.m4 (gl_FUNC_LOG10_WORKS): New macro.
+	(gl_FUNC_LOG10): Invoke it. Set REPLACE_LOG10.
+	* m4/math_h.m4 (gl_MATH_H): Test whether log10 is declared.
+	(gl_MATH_H_DEFAULTS): Initialize GNULIB_LOG10, REPLACE_LOG10.
+	* modules/math (Makefile.am): Substitute GNULIB_LOG10, REPLACE_LOG10.
+	* modules/log10 (Files): Add lib/log10.c.
+	(Depends-on): Add math.
+	(configure.ac): If REPLACE_LOG10 is 1, compile an override.
+	* tests/test-math-c++.cc: Check the declaration of log10.
+	* doc/posix-functions/log10.texi: Mention the OSF/1 5.1 problem.
+
 2012-03-31  Bruno Haible  <bruno@clisp.org>
 
 	log10l tests: More tests.

--- a/doc/posix-functions/log10.texi
+++ b/doc/posix-functions/log10.texi
@@ -8,6 +8,9 @@
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+This function returns a wrong value for a minus zero argument on some platforms:
+OSF/1 5.1.
 @end itemize
 
 Portability problems not fixed by Gnulib:

new file mode 100644
--- /dev/null
+++ b/lib/log10.c
@@ -0,0 +1,31 @@
+/* Base 10 logarithmic function.
+   Copyright (C) 2012 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
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <math.h>
+
+double
+log10 (double x)
+#undef log10
+{
+  /* Work around the OSF/1 5.1 bug.  */
+  if (x == 0.0)
+    /* Return -Infinity.  */
+    return -1.0 / 0.0;
+  return log10 (x);
+}

--- a/lib/math.in.h
+++ b/lib/math.in.h
@@ -1205,6 +1205,26 @@
 # endif
 #endif
 
+#if @GNULIB_LOG10@
+# if @REPLACE_LOG10@
+#  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
+#   undef log10
+#   define log10 rpl_log10
+#  endif
+_GL_FUNCDECL_RPL (log10, double, (double x));
+_GL_CXXALIAS_RPL (log10, double, (double x));
+# else
+_GL_CXXALIAS_SYS (log10, double, (double x));
+# endif
+_GL_CXXALIASWARN (log10);
+#elif defined GNULIB_POSIXCHECK
+# undef log10
+# if HAVE_RAW_DECL_LOG10
+_GL_WARN_ON_USE (log10, "log10 has portability problems - "
+                 "use gnulib module log10 for portability");
+# endif
+#endif
+
 #if @GNULIB_LOG10L@
 # if !@HAVE_LOG10L@ || !@HAVE_DECL_LOG10L@
 #  undef log10l

--- a/m4/log10.m4
+++ b/m4/log10.m4
@@ -1,4 +1,4 @@
-# log10.m4 serial 1
+# log10.m4 serial 2
 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 +6,49 @@
 
 AC_DEFUN([gl_FUNC_LOG10],
 [
+  AC_REQUIRE([gl_MATH_H_DEFAULTS])
+
   dnl Determine LOG10_LIBM.
   gl_COMMON_DOUBLE_MATHFUNC([log10])
+
+  save_LIBS="$LIBS"
+  LIBS="$LIBS $LOG10_LIBM"
+  gl_FUNC_LOG10_WORKS
+  LIBS="$save_LIBS"
+  case "$gl_cv_func_log10_works" in
+    *yes) ;;
+    *) REPLACE_LOG10=1 ;;
+  esac
 ])
+
+dnl Test whether log10() works.
+dnl On OSF/1 5.1, log10(-0.0) is NaN.
+AC_DEFUN([gl_FUNC_LOG10_WORKS],
+[
+  AC_REQUIRE([AC_PROG_CC])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_CACHE_CHECK([whether log10 works], [gl_cv_func_log10_works],
+    [
+      AC_RUN_IFELSE(
+        [AC_LANG_SOURCE([[
+#include <math.h>
+volatile double x;
+double y;
+int main ()
+{
+  x = -0.0;
+  y = log10 (x);
+  if (!(y + y == y))
+    return 1;
+  return 0;
+}
+]])],
+        [gl_cv_func_log10_works=yes],
+        [gl_cv_func_log10_works=no],
+        [case "$host_os" in
+           osf*) gl_cv_func_log10_works="guessing no";;
+           *)    gl_cv_func_log10_works="guessing yes";;
+         esac
+        ])
+    ])
+])

--- a/m4/math_h.m4
+++ b/m4/math_h.m4
@@ -1,4 +1,4 @@
-# math_h.m4 serial 104
+# math_h.m4 serial 105
 dnl Copyright (C) 2007-2012 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -45,7 +45,7 @@
      fabsf fabsl floorf floorl fma fmaf fmal
      fmod fmodf fmodl frexpf frexpl hypotf hypotl
      ldexpf ldexpl
-     logb log logf logl log10f log10l log1p log1pf log1pl log2 log2f log2l
+     logb log logf logl log10 log10f log10l log1p log1pf log1pl log2 log2f log2l
      modf modff modfl powf
      remainder remainderf remainderl
      rint rintf rintl round roundf roundl sinf sinl sinhf sqrtf sqrtl
@@ -119,6 +119,7 @@
   GNULIB_LOG=0;        AC_SUBST([GNULIB_LOG])
   GNULIB_LOGF=0;       AC_SUBST([GNULIB_LOGF])
   GNULIB_LOGL=0;       AC_SUBST([GNULIB_LOGL])
+  GNULIB_LOG10=0;      AC_SUBST([GNULIB_LOG10])
   GNULIB_LOG10F=0;     AC_SUBST([GNULIB_LOG10F])
   GNULIB_LOG10L=0;     AC_SUBST([GNULIB_LOG10L])
   GNULIB_LOG1P=0;      AC_SUBST([GNULIB_LOG1P])
@@ -277,6 +278,7 @@
   REPLACE_LOG=0;               AC_SUBST([REPLACE_LOG])
   REPLACE_LOGF=0;              AC_SUBST([REPLACE_LOGF])
   REPLACE_LOGL=0;              AC_SUBST([REPLACE_LOGL])
+  REPLACE_LOG10=0;             AC_SUBST([REPLACE_LOG10])
   REPLACE_LOG1P=0;             AC_SUBST([REPLACE_LOG1P])
   REPLACE_LOG1PF=0;            AC_SUBST([REPLACE_LOG1PF])
   REPLACE_LOG1PL=0;            AC_SUBST([REPLACE_LOG1PL])

--- a/modules/log10
+++ b/modules/log10
@@ -2,13 +2,19 @@
 log10() function: base 10 logarithmic function.
 
 Files:
+lib/log10.c
 m4/log10.m4
 m4/mathfunc.m4
 
 Depends-on:
+math
 
 configure.ac:
 gl_FUNC_LOG10
+if test $REPLACE_LOG10 = 1; then
+  AC_LIBOBJ([log10])
+fi
+gl_MATH_MODULE_INDICATOR([log10])
 
 Makefile.am:
 

--- a/modules/math
+++ b/modules/math
@@ -84,6 +84,7 @@
 	      -e 's/@''GNULIB_LOG''@/$(GNULIB_LOG)/g' \
 	      -e 's/@''GNULIB_LOGF''@/$(GNULIB_LOGF)/g' \
 	      -e 's/@''GNULIB_LOGL''@/$(GNULIB_LOGL)/g' \
+	      -e 's/@''GNULIB_LOG10''@/$(GNULIB_LOG10)/g' \
 	      -e 's/@''GNULIB_LOG10F''@/$(GNULIB_LOG10F)/g' \
 	      -e 's/@''GNULIB_LOG10L''@/$(GNULIB_LOG10L)/g' \
 	      -e 's/@''GNULIB_LOG1P''@/$(GNULIB_LOG1P)/g' \
@@ -244,6 +245,7 @@
 	      -e 's|@''REPLACE_LOG''@|$(REPLACE_LOG)|g' \
 	      -e 's|@''REPLACE_LOGF''@|$(REPLACE_LOGF)|g' \
 	      -e 's|@''REPLACE_LOGL''@|$(REPLACE_LOGL)|g' \
+	      -e 's|@''REPLACE_LOG10''@|$(REPLACE_LOG10)|g' \
 	      -e 's|@''REPLACE_LOG1P''@|$(REPLACE_LOG1P)|g' \
 	      -e 's|@''REPLACE_LOG1PF''@|$(REPLACE_LOG1PF)|g' \
 	      -e 's|@''REPLACE_LOG1PL''@|$(REPLACE_LOG1PL)|g' \

--- a/tests/test-math-c++.cc
+++ b/tests/test-math-c++.cc
@@ -210,7 +210,9 @@
 
 //SIGNATURE_CHECK (GNULIB_NAMESPACE::lgamma, double, (double));
 
-//SIGNATURE_CHECK (GNULIB_NAMESPACE::log10, double, (double));
+#if GNULIB_TEST_LOG10
+SIGNATURE_CHECK (GNULIB_NAMESPACE::log10, double, (double));
+#endif
 #if GNULIB_TEST_LOG10L
 SIGNATURE_CHECK (GNULIB_NAMESPACE::log10l, long double, (long double));
 #endif