sbcl unicode

I noticed the following code in strings.lisp:

#+(and sbcl sb-unicode)
(defun sbcl-naturalize-cstring (sap &key length (null-terminated-p t))
...
            ;; this will not work in sb-unicode
            (sb-kernel:copy-from-system-area sap 0
                                             result (* sb-vm:vector-data-offset
                                                       sb-vm:n-word-bits)
                                             (* length sb-vm:n-byte-bits))

what's the status of this?  how should one efficiently convert from a
known ucs4 alien byte array to a unicode sbcl string?

take care, B