(logior x (ash y 8) (ash z 16) (ash w 24))))

(eval-when (expand)
  (define-syntax pack-flags
    (syntax-rules ()
      ;; Add clauses as needed.
      ((pack-flags f1 f2) (logior (if f1 (ash 1 0) 0)
                                  (if f2 (ash 1 1) 0))))))


(define-syntax-rule (define-byte-order-swapper name size ref set)
  (define* (name buf #:optional (start 0) (end (bytevector-length buf)))
    "Patch up the text buffer @var{buf}, swapping the endianness of each
N-byte unit."
    (unless (zero? (modulo (- end start) size))
      (error "unexpected length"))
    (let lp ((pos start))
      (when (< pos end)
        (set buf pos (ref buf pos (endianness big)) (endianness little))
        (lp (+ pos size))))))

(define-byte-order-swapper byte-swap/2!
  2 bytevector-u16-ref bytevector-u16-set!)
(define-byte-order-swapper byte-swap/4!
  4 bytevector-u32-ref bytevector-u32-set!)
(define-byte-order-swapper byte-swap/8!
  8 bytevector-u64-ref bytevector-u64-set!)