added FFTW2 support

cmake/CMakeLists.txt

@@ -116,17 +116,15 @@ if(ENABLE_USER-OMP OR ENABLE_KOKKOS OR ENABLE_USER-INTEL)
 endif()
 
 if(ENABLE_KSPACE)
-  find_package(FFTW3)
-  find_package(MKL)
-  if(FFTW3_FOUND)
-    add_definitions(-DFFT_FFTW3)
-    include_directories(${FFTW3_INCLUDE_DIRS})
-    list(APPEND LAMMPS_LINK_LIBS ${FFTW3_LIBRARIES})
-  elseif(MKL_FOUND)
-    add_definitions(-DFFT_MKL)
-    include_directories(${MKL_INCLUDE_DIRS})
-    list(APPEND LAMMPS_LINK_LIBS ${MKL_LIBRARIES})
-  endif()
+  foreach(FFT FFTW3 MKL FFTW2)
+    find_package(${FFT})
+    if(${FFT}_FOUND)
+      add_definitions(-DFFT_${FFT})
+      include_directories(${${FFT}_INCLUDE_DIRS})
+      list(APPEND LAMMPS_LINK_LIBS ${${FFT}_LIBRARIES})
+      break()
+    endif()
+  endforeach()
   set(PACK_OPTIMIZATION "PACK_ARRAY" CACHE STRING "Optimization for FFT")
   set_property(CACHE LAMMPS_SIZE_LIMIT PROPERTY STRINGS PACK_ARRAY PACK_POINTER PACK_MEMCPY)
   if(NOT PACK_OPTIMIZATION STREQUAL "PACK_ARRAY")

cmake/Modules/FindFFTW2.cmake

@@ -0,0 +1,22 @@
+# - Find fftw2
+# Find the native FFTW2 headers and libraries.
+#
+#  FFTW2_INCLUDE_DIRS - where to find fftw2.h, etc.
+#  FFTW2_LIBRARIES    - List of libraries when using fftw2.
+#  FFTW2_FOUND        - True if fftw2 found.
+#
+
+find_path(FFTW2_INCLUDE_DIR fftw.h)
+
+find_library(FFTW2_LIBRARY NAMES fftw)
+
+set(FFTW2_LIBRARIES ${FFTW2_LIBRARY})
+set(FFTW2_INCLUDE_DIRS ${FFTW2_INCLUDE_DIR})
+
+include(FindPackageHandleStandardArgs)
+# handle the QUIETLY and REQUIRED arguments and set FFTW2_FOUND to TRUE
+# if all listed variables are TRUE
+
+find_package_handle_standard_args(FFTW2 DEFAULT_MSG FFTW2_LIBRARY FFTW2_INCLUDE_DIR)
+
+mark_as_advanced(FFTW2_INCLUDE_DIR FFTW2_LIBRARY )