From c2827e56b982a96d3c1a6d803f0c93b19ead9014 Mon Sep 17 00:00:00 2001
From: Daniel Arndt <daniel.arndt@iwr.uni-heidelberg.de>
Date: Tue, 7 Aug 2018 10:32:23 +0200
Subject: [PATCH] Fix preprocessor directive

---
 cmake/checks/check_01_cxx_features.cmake | 1 -
 include/deal.II/base/std_cxx17/cmath.h   | 8 ++++----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/cmake/checks/check_01_cxx_features.cmake b/cmake/checks/check_01_cxx_features.cmake
index 2236748438..9b44082564 100644
--- a/cmake/checks/check_01_cxx_features.cmake
+++ b/cmake/checks/check_01_cxx_features.cmake
@@ -213,7 +213,6 @@ IF(NOT DEFINED DEAL_II_WITH_CXX17 OR DEAL_II_WITH_CXX17)
 
   IF( DEAL_II_HAVE_CXX17_ATTRIBUTES AND
       DEAL_II_HAVE_CXX17_IF_CONSTEXPR AND
-      DEAL_II_HAVE_CXX17_SPECIAL_MATH_FUNCTIONS AND
       DEAL_II_NON_CONSTEXPR_LAMBDA)
     SET(DEAL_II_HAVE_CXX17 TRUE)
   ELSE()
diff --git a/include/deal.II/base/std_cxx17/cmath.h b/include/deal.II/base/std_cxx17/cmath.h
index 394a2ac814..2a71062981 100644
--- a/include/deal.II/base/std_cxx17/cmath.h
+++ b/include/deal.II/base/std_cxx17/cmath.h
@@ -17,16 +17,16 @@
 
 #include <deal.II/base/config.h>
 
-#ifndef DEAL_II_WITH_CXX17
+#ifndef DEAL_II_HAVE_CXX17_SPECIAL_MATH_FUNCTIONS
 #  include <boost/math/special_functions/bessel.hpp>
-#endif // DEAL_II_WITH_CXX17
+#endif // DEAL_II_HAVE_CXX17_SPECIAL_MATH_FUNCTIONS
 
 #include <cmath>
 
 DEAL_II_NAMESPACE_OPEN
 namespace std_cxx17
 {
-#ifdef DEAL_II_HAVE_CXX17_SPECIAL_MATH_FUNCTIONS
+#ifndef DEAL_II_HAVE_CXX17_SPECIAL_MATH_FUNCTIONS
   double (&cyl_bessel_j)(double,
                          double) = boost::math::cyl_bessel_j<double, double>;
   float (&cyl_bessel_jf)(float,
@@ -37,7 +37,7 @@ namespace std_cxx17
   using std::cyl_bessel_j;
   using std::cyl_bessel_jf;
   using std::cyl_bessel_jl;
-#endif
+#endif // DEAL_II_HAVE_CXX17_SPECIAL_MATH_FUNCTIONS
 } // namespace std_cxx17
 DEAL_II_NAMESPACE_CLOSE
 
-- 
2.39.5