math: Ensure declarations of math functions.

[gnulib.git] / m4 / copysignf.m4

diff --git a/m4/copysignf.m4 b/m4/copysignf.m4
index f706009..4f2825c 100644 (file)
--- a/m4/copysignf.m4
+++ b/m4/copysignf.m4
@@ -1,4 +1,4 @@
-# copysignf.m4 serial 1
+# copysignf.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,
@@ -8,6 +8,9 @@ AC_DEFUN([gl_FUNC_COPYSIGNF],
 [
   AC_REQUIRE([gl_MATH_H_DEFAULTS])
 
+  dnl Persuade glibc <math.h> to declare copysignf().
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
   dnl Determine COPYSIGNF_LIBM.
   gl_MATHFUNC([copysignf], [float], [(float, float)])
   if test $gl_cv_func_copysignf_no_libm = no \