ffi: allow ptr-in-out passing of cptr.

* ffi.c (ffi_ptr_alloc): New static function.
(ffi_type_compile): Give the cptr type alloc and free
functions: alloc just retrives the address of the pointer
inside the cptr object (pointer to pointer); free is a noop.
(cptr_make): New static function.
(ffi_init): Register cptr_make as cptr intrinsic. Register
cptr-null intrinsic variable denoting a ready-made null
pointer.

* lib.c (cptr_addr_of): New function.

* lib.h (cptr_addr_of): Declared.

1 files changed, 6 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index 8eaa81bf..96b18000 100644
--- a/lib.c
+++ b/lib.c
@@ -7361,6 +7361,12 @@ mem_t *cptr_get(val cptr)
   return cobj_handle(cptr, cptr_s);
 }
 
+mem_t **cptr_addr_of(val cptr)
+{
+  (void) cobj_handle(cptr, cptr_s);
+  return &cptr->co.handle;
+}
+
 val assoc(val key, val list)
 {
   list = nullify(list);