New example for using CFFI

examples/ffi/cffi.lsp

@@ -0,0 +1,27 @@
+#|
+Build and load this module with (compile-file "cffi.lsp" :load t)
+|#
+;;
+;; This toplevel statement notifies the compiler that we will
+;; need this shared library at runtime. We do not need this
+;; statement in windows.
+;;
+#-(or ming32 windows)
+(cffi:load-foreign-library #+darwin "/usr/lib/libm.dylib"
+			   #-darwin "/usr/lib/libm.so")
+;;
+;; With this other statement, we import the C function sin(),
+;; which operates on IEEE doubles.
+;;
+(cffi:defcfun ("sin" c-sin) :double :double)
+;;
+;; We now use this function and compare with the lisp version.
+;;
+(format t "~%Lisp sin:~t~d~%C sin:~t~d~%Difference:~t~d"
+	(sin 1.0d0) (c-sin 1.0d0) (- (sin 1.0d0) (c-sin 1.0d0)))
+;;
+;; The following also works: no declaration!
+;;
+(let ((c-cos (cffi:foreign-funcall "cos" :double 1.0d0 :double)))
+   (format t "~%Lisp cos:~t~d~%C cos:~t~d~%Difference:~t~d"
+	(sin 1.0d0) c-sin (- (sin 1.0d0) c-sin)))