math: Ensure declarations of math functions.

[gnulib.git] / m4 / tanf.m4

diff --git a/m4/tanf.m4 b/m4/tanf.m4
index 7ecbe81..030abe9 100644 (file)
--- a/m4/tanf.m4
+++ b/m4/tanf.m4
@@ -1,4 +1,4 @@
-# tanf.m4 serial 1
+# tanf.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,
@@ -9,6 +9,9 @@ AC_DEFUN([gl_FUNC_TANF],
   AC_REQUIRE([gl_MATH_H_DEFAULTS])
   AC_REQUIRE([gl_FUNC_TAN])
 
+  dnl Persuade glibc <math.h> to declare tanf().
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
   dnl Test whether tanf() exists. Assume that tanf(), if it exists, is
   dnl defined in the same library as tan().
   save_LIBS="$LIBS"