add -lm as needed (#55)

* hack add -lm to linux build

* proper lm detection

* better -lm detection

Author: loriab

CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.1 FATAL_ERROR)
 
 project(gau2grid
-        VERSION 2.0.1
+        VERSION 2.0.3
         LANGUAGES C)
 set(gau2grid_AUTHORS      "Daniel G. A. Smith")
 set(gau2grid_DESCRIPTION  "Fast computation of a gaussian and its derivative on a grid")
@@ -88,6 +88,9 @@ endif()
 set_target_properties(gg PROPERTIES POSITION_INDEPENDENT_CODE ${BUILD_FPIC}
                                     SOVERSION 1)  # bump whenever interface has changes or removals
 
+find_package(StandardMathLibraryC)
+target_link_libraries(gg PRIVATE ${STANDARD_MATH_LIBRARY})
+
 if(${BUILD_SHARED_LIBS})
     target_link_libraries(gg PRIVATE ${LIBC_INTERJECT})
 endif()

cmake/FindStandardMathLibraryC.cmake

@@ -0,0 +1,54 @@
+# * downloaded Nov 2016 from https://android.googlesource.com/platform/external/eigen/+/master/cmake/FindStandardMathLibrary.cmake
+# * changed CXX to C
+# * note that full path to libm *not* detected
+
+# - 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 <[email protected]>
+# Redistribution and use is allowed according to the terms of the 2-clause BSD license.
+include(CheckCSourceCompiles)
+# 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<math.h>
+int main() { sin(0.0); log(0.0f); }")
+# C++ 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_C_SOURCE_COMPILES(
+  "${find_standard_math_library_test_program}"
+  standard_math_library_linked_to_automatically
+)
+if(standard_math_library_linked_to_automatically)
+  # the test program linked successfully without any linker flag.
+  set(STANDARD_MATH_LIBRARY "")
+  set(STANDARD_MATH_LIBRARY_FOUND TRUE)
+else()
+  # the test program did not link successfully without any linker flag.
+  # This is a very uncommon case that so far we only saw on QNX. The next try is the
+  # standard name 'm' for the standard math library.
+  set(CMAKE_REQUIRED_LIBRARIES "m")
+  CHECK_C_SOURCE_COMPILES(
+    "${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()