Source code in the clojure programming language

(defn gcd 
  "(gcd a b) computes the greatest common divisor of a and b."
  [a b]
  (if (zero? b)
    a
    (recur b (mod a b))))


(defn gcd*
  "greatest common divisor of a list of numbers"
  [& lst]
  (reduce gcd
          lst))


(defn stein-gcd [a b]
  (cond
    (zero? a) b
    (zero? b) a
    (and (even? a) (even? b)) (* 2 (stein-gcd (unsigned-bit-shift-right a 1) (unsigned-bit-shift-right b 1)))
    (and (even? a) (odd? b)) (recur (unsigned-bit-shift-right a 1) b)
    (and (odd? a) (even? b)) (recur a (unsigned-bit-shift-right b 1))
    (and (odd? a) (odd? b)) (recur (unsigned-bit-shift-right (Math/abs (- a b)) 1) (min a b))))