--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2012-03-07  Bruno Haible  <bruno@clisp.org>
+
+	roundf: Don't override undeclared system function on IRIX 6.5.
+	* m4/roundf.m4 (gl_FUNC_ROUNDF): Search for roundf() in the libraries
+	also when it is not declared. Set HAVE_ROUNDF. For replacement code,
+	test HAVE_ROUNDF, not HAVE_DECL_ROUNDF.
+	* modules/roundf (configure.ac): For replacement code, test
+	HAVE_ROUNDF, not HAVE_DECL_ROUNDF.
+	(Depends-on): Update conditions.
+	* modules/roundf-ieee (Depends-on): Update conditions.
+	* doc/posix-functions/roundf.texi: Mention the IRIX problem.
+
 2012-03-07  Bruno Haible  <bruno@clisp.org>
 
 	round: Don't override undeclared system function on IRIX 6.5.

--- a/doc/posix-functions/roundf.texi
+++ b/doc/posix-functions/roundf.texi
@@ -10,10 +10,10 @@
 @itemize
 @item
 This function is missing on some platforms:
-FreeBSD 5.2.1, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, HP-UX 11, IRIX 6.5, OSF/1 4.0, Solaris 9, MSVC 9, Interix 3.5.
+FreeBSD 5.2.1, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, HP-UX 11, older IRIX 6.5, OSF/1 4.0, Solaris 9, MSVC 9, Interix 3.5.
 @item
 This function is not declared on some platforms:
-glibc 2.8, OSF/1 5.1.
+glibc 2.8, IRIX 6.5, OSF/1 5.1.
 @item
 This functions returns a wrong result for x = 1/2 - 2^-25 on some platforms:
 mingw.

--- a/m4/roundf.m4
+++ b/m4/roundf.m4
@@ -1,4 +1,4 @@
-# roundf.m4 serial 15
+# roundf.m4 serial 16
 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,
@@ -8,23 +8,39 @@
 [
   m4_divert_text([DEFAULTS], [gl_roundf_required=plain])
   AC_REQUIRE([gl_MATH_H_DEFAULTS])
+
   dnl Persuade glibc <math.h> to declare roundf().
   AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
-  AC_CHECK_DECLS([roundf], , , [[#include <math.h>]])
-  if test "$ac_cv_have_decl_roundf" = yes; then
-    gl_CHECK_MATH_LIB([ROUNDF_LIBM], [x = roundf (x);])
-    if test "$ROUNDF_LIBM" != missing; then
-      dnl Test whether roundf() produces correct results. On mingw, for
-      dnl x = 1/2 - 2^-25, the system's roundf() returns a wrong result.
-      AC_REQUIRE([AC_PROG_CC])
-      AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
-      AC_CACHE_CHECK([whether roundf works], [gl_cv_func_roundf_works],
-        [
-          save_LIBS="$LIBS"
-          LIBS="$LIBS $ROUNDF_LIBM"
-          AC_RUN_IFELSE([AC_LANG_SOURCE([[
+
+  gl_CHECK_MATH_LIB([ROUNDF_LIBM], [x = roundf (x);],
+    [extern
+     #ifdef __cplusplus
+     "C"
+     #endif
+     float roundf (float);
+    ])
+  if test "$ROUNDF_LIBM" != missing; then
+    HAVE_ROUNDF=1
+    dnl Also check whether it's declared.
+    dnl IRIX 6.5 has roundf() in libm but doesn't declare it in <math.h>.
+    AC_CHECK_DECLS([roundf], , [HAVE_DECL_ROUNDF=0], [[#include <math.h>]])
+
+    dnl Test whether roundf() produces correct results. On mingw, for
+    dnl x = 1/2 - 2^-25, the system's roundf() returns a wrong result.
+    AC_REQUIRE([AC_PROG_CC])
+    AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+    AC_CACHE_CHECK([whether roundf works], [gl_cv_func_roundf_works],
+      [
+        save_LIBS="$LIBS"
+        LIBS="$LIBS $ROUNDF_LIBM"
+        AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <float.h>
 #include <math.h>
+extern
+#ifdef __cplusplus
+"C"
+#endif
+float roundf (float);
 #ifdef _MSC_VER
 # pragma fenv_access (off)
 #endif
@@ -40,20 +56,17 @@
   volatile float x = 0.5f - 0.5f / TWO_MANT_DIG;
   exit (x < 0.5f && roundf (x) != 0.0f);
 }]])], [gl_cv_func_roundf_works=yes], [gl_cv_func_roundf_works=no],
-          [case "$host_os" in
-             mingw*) gl_cv_func_roundf_works="guessing no";;
-             *)      gl_cv_func_roundf_works="guessing yes";;
-           esac
-          ])
-          LIBS="$save_LIBS"
+        [case "$host_os" in
+           mingw*) gl_cv_func_roundf_works="guessing no";;
+           *)      gl_cv_func_roundf_works="guessing yes";;
+         esac
         ])
-      case "$gl_cv_func_roundf_works" in
-        *no) ROUNDF_LIBM=missing ;;
-      esac
-    fi
-    if test "$ROUNDF_LIBM" = missing; then
-      REPLACE_ROUNDF=1
-    fi
+        LIBS="$save_LIBS"
+      ])
+    case "$gl_cv_func_roundf_works" in
+      *no) REPLACE_ROUNDF=1 ;;
+    esac
+
     m4_ifdef([gl_FUNC_ROUNDF_IEEE], [
       if test $gl_roundf_required = ieee && test $REPLACE_ROUNDF = 0; then
         AC_CACHE_CHECK([whether roundf works according to ISO C 99 with IEC 60559],
@@ -67,6 +80,11 @@
 # define __NO_MATH_INLINES 1 /* for glibc */
 #endif
 #include <math.h>
+extern
+#ifdef __cplusplus
+"C"
+#endif
+float roundf (float);
 ]gl_FLOAT_MINUS_ZERO_CODE[
 ]gl_FLOAT_SIGNBIT_CODE[
 static float dummy (float f) { return 0; }
@@ -95,9 +113,10 @@
       fi
     ])
   else
+    HAVE_ROUNDF=0
     HAVE_DECL_ROUNDF=0
   fi
-  if test $HAVE_DECL_ROUNDF = 0 || test $REPLACE_ROUNDF = 1; then
+  if test $HAVE_ROUNDF = 0 || test $REPLACE_ROUNDF = 1; then
     dnl Find libraries needed to link lib/roundf.c.
     AC_CHECK_DECLS([ceilf, floorf], , , [[#include <math.h>]])
     if test "$ac_cv_have_decl_floorf" = yes \

--- a/modules/roundf
+++ b/modules/roundf
@@ -12,11 +12,11 @@
 Depends-on:
 math
 extensions
-float           [test $HAVE_DECL_ROUNDF = 0 || test $REPLACE_ROUNDF = 1]
+float           [test $HAVE_ROUNDF = 0 || test $REPLACE_ROUNDF = 1]
 
 configure.ac:
 gl_FUNC_ROUNDF
-if test $HAVE_DECL_ROUNDF = 0 || test $REPLACE_ROUNDF = 1; then
+if test $HAVE_ROUNDF = 0 || test $REPLACE_ROUNDF = 1; then
   AC_LIBOBJ([roundf])
 fi
 gl_MATH_MODULE_INDICATOR([roundf])

--- a/modules/roundf-ieee
+++ b/modules/roundf-ieee
@@ -8,8 +8,8 @@
 
 Depends-on:
 roundf
-floorf-ieee     [test $HAVE_DECL_ROUNDF = 0 || test $REPLACE_ROUNDF = 1]
-ceilf-ieee      [test $HAVE_DECL_ROUNDF = 0 || test $REPLACE_ROUNDF = 1]
+floorf-ieee     [test $HAVE_ROUNDF = 0 || test $REPLACE_ROUNDF = 1]
+ceilf-ieee      [test $HAVE_ROUNDF = 0 || test $REPLACE_ROUNDF = 1]
 
 configure.ac:
 gl_FUNC_ROUNDF_IEEE