Fix undefined reference to `__atomic_fetch_add_8' (#46)

* Find libatomic

* Improve libatomic detection

* Use -std=c++11  to compile <atomic>

* Refactor libatomic detection

* Changes in version 6.3

* Use CMAKE_REQUIRED_FLAGS instead of CMAKE_REQUIRED_DEFINITIONS

CMakeLists.txt

@@ -57,12 +57,39 @@ if(no_fallthrough)
     set_source_files_properties(src/primesieve/EratSmall.cpp PROPERTIES COMPILE_FLAGS -Wno-implicit-fallthrough)
 endif()
 
+# Check if libatomic is needed #######################################
+
+include(CheckCXXSourceCompiles)
+
+set(CMAKE_OLD_FLAGS ${CMAKE_REQUIRED_FLAGS})
+set(CMAKE_REQUIRED_FLAGS ${CMAKE_CXX11_STANDARD_COMPILE_OPTION})
+
+check_cxx_source_compiles("
+    #include <atomic>
+    int main() {
+        std::atomic<int> x;
+        x = 1;
+        x--;
+        return x;
+    }"
+    have_atomic)
+
+set(CMAKE_REQUIRED_FLAGS ${CMAKE_OLD_FLAGS})
+
+if(NOT have_atomic)
+    find_library(ATOMIC NAMES atomic libatomic.so libatomic.so.1)
+    if(ATOMIC)
+        set(LIBATOMIC ${ATOMIC})
+        message(STATUS "Found libatomic: TRUE")
+    endif()
+endif()
+
 # libprimesieve ######################################################
 
 add_library(libprimesieve ${LIB_SRC})
 set_target_properties(libprimesieve PROPERTIES OUTPUT_NAME primesieve)
 find_package(Threads REQUIRED)
-target_link_libraries(libprimesieve Threads::Threads)
+target_link_libraries(libprimesieve Threads::Threads ${LIBATOMIC})
 
 target_include_directories(libprimesieve PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
@@ -83,7 +110,7 @@ install(TARGETS libprimesieve
 if(BUILD_STATIC_LIBS AND BUILD_SHARED_LIBS)
     add_library(static_libprimesieve STATIC ${LIB_SRC})
     set_target_properties(static_libprimesieve PROPERTIES OUTPUT_NAME primesieve)
-    target_link_libraries(static_libprimesieve Threads::Threads)
+    target_link_libraries(static_libprimesieve Threads::Threads ${LIBATOMIC})
 
     target_include_directories(static_libprimesieve PUBLIC
         $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>

ChangeLog

@@ -1,3 +1,14 @@
+Changes in version 6.3, 12/11/2017
+==================================
+
+This is a minor new release, the API and ABI are
+backwards compatible.
+
+ * test/ilog2.cpp: Fix Linux i386 bug.
+ * test/floorPower2.cpp: Fix Linux i386 bug.
+ * CMakeLists.txt: Link against libatomic if needed.
+ * CMakeLists.txt: Add Debian Multiarch support.
+
 Changes in version 6.2, 12/10/2017
 ==================================