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(ns bitarray
(:use clojure.test))
(defstruct bit-field :element-width :array-data)
(defn bit-array
[n]
(struct bit-field 31 (int-array (inc (int (/ n 31))))))
(defn set-bit!
[bitfield bit val]
(let [r (mod bit (bitfield :element-width))
n (int (/ bit (bitfield :element-width)))
x (aget (bitfield :array-data) n)]
(if (not (zero? val))
(aset (bitfield :array-data) n (bit-or x (bit-shift-left 1 r)))
(aset (bitfield :array-data) n (bit-xor x (bit-shift-left 1 r))))
bitfield))
(defn get-bit
[bitfield bit]
(let [r (mod bit (bitfield :element-width))
x (aget (bitfield :array-data) (int (/ bit (bitfield :element-width))))]
(if (= 0 (bit-and x (bit-shift-left 1 r))) 0 1)))
(deftest test-bits
(let [n 32
f (bit-array n)]
(is (= 31 (f :element-width)))
(doseq [x (range 0 n)]
(is (= 0 (get-bit f x))))
(doseq [x (reverse (range 0 n))]
(set-bit! f x 1)
(is (= 1 (get-bit f x))))
(doseq [x (range 0 n)]
(set-bit! f x 0)
(is (= 0 (get-bit f x))))))
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