(let* ((len (read-arg 4))
(sizebits (read-arg 1))
(type (case sizebits
+ (0 sb!vm:simple-array-nil-widetag)
(1 sb!vm:simple-bit-vector-widetag)
(2 sb!vm:simple-array-unsigned-byte-2-widetag)
(4 sb!vm:simple-array-unsigned-byte-4-widetag)
+ (7 (prog1 sb!vm:simple-array-unsigned-byte-7-widetag
+ (setf sizebits 8)))
(8 sb!vm:simple-array-unsigned-byte-8-widetag)
+ (15 (prog1 sb!vm:simple-array-unsigned-byte-15-widetag
+ (setf sizebits 16)))
(16 sb!vm:simple-array-unsigned-byte-16-widetag)
+ (31 (prog1 sb!vm:simple-array-unsigned-byte-31-widetag
+ (setf sizebits 32)))
(32 sb!vm:simple-array-unsigned-byte-32-widetag)
(t (error "losing element size: ~W" sizebits))))
(result (allocate-vector-object *dynamic* sizebits len type))