cmake: add FFT_SINGLE option

cmake/CMakeLists.txt

@@ -166,11 +166,26 @@ if(BUILD_OMP OR ENABLE_USER-OMP OR ENABLE_KOKKOS OR ENABLE_USER-INTEL)
 endif()
 
 if(ENABLE_KSPACE)
-  set(FFT "KISSFFT" CACHE STRING "FFT library for KSPACE package")
-  set_property(CACHE FFT PROPERTY STRINGS KISSFFT FFTW3 MKL)
+  option(FFT_SINGLE "Use single precision FFT instead of double" OFF)
+  set(FFTW "FFTW3")
+  if(FFT_SINGLE)
+    set(FFTW "FFTW3F")
+    add_definitions(-DFFT_SINGLE)
+  endif()
+  find_package(${FFTW} QUIET)
+  if(${FFTW}_FOUND)
+    set(FFT "${{FFTW}" CACHE STRING "FFT library for KSPACE package")
+  else()
+    set(FFT "KISSFFT" CACHE STRING "FFT library for KSPACE package")
+  endif()
+  set_property(CACHE FFT PROPERTY STRINGS KISSFFT ${FFTW} MKL)
   if(NOT FFT STREQUAL "KISSFFT")
     find_package(${FFT} REQUIRED)
-    add_definitions(-DFFT_${FFT})
+    if(NOT FFT STREQUAL "FFTW3F")
+	    add_definitions(-DFFT_FFTW)
+    else()
+      add_definitions(-DFFT_${FFT})
+    endif()
     include_directories(${${FFT}_INCLUDE_DIRS})
     list(APPEND LAMMPS_LINK_LIBS ${${FFT}_LIBRARIES})
   endif()

cmake/Modules/FindFFTW3F.cmake

@@ -0,0 +1,25 @@
+# - Find fftw3f
+# Find the native FFTW3F headers and libraries.
+#
+#  FFTW3F_INCLUDE_DIRS - where to find fftw3f.h, etc.
+#  FFTW3F_LIBRARIES    - List of libraries when using fftw3f.
+#  FFTW3F_FOUND        - True if fftw3f found.
+#
+
+find_package(PkgConfig)
+
+pkg_check_modules(PC_FFTW3F fftw3f)
+find_path(FFTW3F_INCLUDE_DIR fftw3f.h HINTS ${PC_FFTW3F_INCLUDE_DIRS})
+
+find_library(FFTW3F_LIBRARY NAMES fftw3f HINTS ${PC_FFTW3F_LIBRARY_DIRS})
+
+set(FFTW3F_LIBRARIES ${FFTW3F_LIBRARY})
+set(FFTW3F_INCLUDE_DIRS ${FFTW3F_INCLUDE_DIR})
+
+include(FindPackageHandleStandardArgs)
+# handle the QUIETLY and REQUIRED arguments and set FFTW3F_FOUND to TRUE
+# if all listed variables are TRUE
+
+find_package_handle_standard_args(FFTW3F DEFAULT_MSG FFTW3F_LIBRARY FFTW3F_INCLUDE_DIR)
+
+mark_as_advanced(FFTW3F_INCLUDE_DIR FFTW3F_LIBRARY )