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.

1 files changed, 47 insertions, 28 deletions

diff --git a/m4/roundf.m4 b/m4/roundf.m4
index 58f4287bb8..fc07b762ce 100644
--- 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 @@ AC_DEFUN([gl_FUNC_ROUNDF],
 [
   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 $ROUNDF_LIBM"
+        AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <float.h>
 #include <math.h>
+extern
+#ifdef __cplusplus
+"C"
+#endif
+float roundf (float);
 #ifdef _MSC_VER
 # pragma fenv_access (off)
 #endif
@@ -40,20 +56,17 @@ int main()
   volatile float x = 0.5f - 0.5f / TWO_MANT_DIG;
   exit (x < 0.5f && roundf (x) != 0.0f);
 }]])], [gl_cv_func_roundf_works=yes], [gl_cv_func_roundf_works=no],
-          [case "$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 @@ int main()
 # 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 @@ int main (int argc, char *argv[])
       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 \