add platform check for how to link to the standard math library.

This allows to support QNX.

1 files changed, 64 insertions, 0 deletions

diff --git a/cmake/FindStandardMathLibrary.cmake b/cmake/FindStandardMathLibrary.cmake
new file mode 100644
index 000000000..711b0e4b4
--- /dev/null
+++ b/cmake/FindStandardMathLibrary.cmake
@@ -0,0 +1,64 @@
+# - Try to find how to link to the standard math library, if anything at all is needed to do.
+# On most platforms this is automatic, but for example it's not automatic on QNX.
+#
+# Once done this will define
+#
+#  STANDARD_MATH_LIBRARY_FOUND - we found how to successfully link to the standard math library
+#  STANDARD_MATH_LIBRARY - the name of the standard library that one has to link to.
+#                            -- this will be left empty if it's automatic (most platforms).
+#                            -- this will be set to "m" on platforms where one must explicitly
+#                               pass the "-lm" linker flag.
+#
+# Copyright (c) 2010 Benoit Jacob <jacob.benoit.1@gmail.com>
+# Redistribution and use is allowed according to the terms of the 2-clause BSD license.
+
+
+include(CheckCXXSourceCompiles)
+
+# a little test program for c++ math functions.
+# notice the std:: is required on some platforms such as QNX
+
+set(find_standard_math_library_test_program
+"#include<cmath>
+int main() { std::sin(0.0); std::log(0.0f); }")
+
+# first try compiling/linking the test program without any linker flags
+
+set(CMAKE_REQUIRED_FLAGS "")
+set(CMAKE_REQUIRED_LIBRARIES "")
+CHECK_CXX_SOURCE_COMPILES(
+  "${find_standard_math_library_test_program}"
+  standard_math_library_linked_to_automatically
+)
+
+if(standard_math_library_linked_to_automatically)
+
+  # the test program linked successfully without any linker flag.
+  set(STANDARD_MATH_LIBRARY "")
+  set(STANDARD_MATH_LIBRARY_FOUND TRUE)
+
+else()
+
+  # the test program did not link successfully without any linker flag.
+  # This is a very uncommon case that so far we only saw on QNX. The next try is the
+  # standard name 'm' for the standard math library.
+
+  set(CMAKE_REQUIRED_LIBRARIES "m")
+  CHECK_CXX_SOURCE_COMPILES(
+    "${find_standard_math_library_test_program}"
+    standard_math_library_linked_to_as_m)
+
+  if(standard_math_library_linked_to_as_m)
+
+    # the test program linked successfully when linking to the 'm' library
+    set(STANDARD_MATH_LIBRARY "m")
+    set(STANDARD_MATH_LIBRARY_FOUND TRUE)
+
+  else()
+
+    # the test program still doesn't link successfully
+    set(STANDARD_MATH_LIBRARY_FOUND FALSE)
+
+  endif()
+
+endif()