Clojureでバイト配列を整数に変換する ref: http://qiita.com/kurogelee/items/919cd0df8b59d7bcf65a

sample.clj

(def << bit-shift-left)
(def >> bit-shift-right)

(defn unsigned [^bytes bytea]
  {:pre [(<= 1 (alength bytea) 7)]}
  (areduce bytea i ret 0
           (bit-or (<< ret 8) (bit-and 0xff (aget bytea i)))))

(defn signed [^bytes bytea]
  {:pre [(<= 1 (alength bytea) 8)]}
  (areduce bytea i ret (if (neg? (aget bytea 0)) -1 0)
           (bit-or (<< ret 8) (bit-and 0xff (aget bytea i)))))

sample2.clj

(defn areverse-byte [^bytes bytea]
  (let [len (alength bytea)]
    (areduce bytea i ret (byte-array len)
             (do (aset-byte ret (- len i 1) (aget bytea i)) ret))))

sample3.clj

(defn ^bytes ->bytes [^long len ^long value]
  {:pre [(<= 1 len 8)]}
  (byte-array
   (reduce (fn [a i] (conj a (>> value (* (- len i 1) 8)))) [] (range len))))