vint.clj

(ns mc.vint)

(def ^:private msb 2r10000000)

(defn read-more?
  [b]
  (-> (bit-and msb b)
      (> 0)))

(defn clear-msb
  [b]
  (bit-and b 2r01111111))

(defn combine-to-int
  ([left right]
   (-> left
       (bit-shift-left 7)
       (bit-or (clear-msb right)))))

(defn read-vint
  [byte-provider]
  (loop [b (byte-provider)
         byte-stack [b]]
    (if (read-more? b)
      (let [next-b (byte-provider)]
        (recur next-b (conj byte-stack next-b)))
      (->> byte-stack
           (reverse)
           (reduce combine-to-int)))))

(defn read-vint-is
  [is]
  (read-vint #(.read is)))

vint_test.clj

(ns mc.vint_test
  (:require [clojure.test :refer :all]
            [mc.vint :refer :all]))

(deftest read-more-test
  (testing "read-more"
    (is (true? (read-more? 2r11110100)))
    (is (true? (read-more? 2r10000001)))
    (is (false? (read-more? 2r01110100)))
    (is (false? (read-more? 2r00000001)))
    (is (false? (read-more? 1)))
    )
  )

(deftest clear-msb-test
  (testing "clear-msb-with-msb"
    (is (= 2r01111111 (clear-msb 2r11111111)))
    (is (= 2r01000001 (clear-msb 2r11000001)))
    (is (= 2r01110100 (clear-msb 2r11110100)))
    )

  (testing "clear-msb-without-msb"
    (is (= 2r01000001 (clear-msb 2r01000001)))
    )
  )

(deftest combine-to-int-test
  (testing "combine-to-int"
    (is (= 2r11101001000001 (combine-to-int 2r01110100 2r01000001)))
    (is (= 2r100001011 (combine-to-int 2r10 2r100001011)))
    (is (= 2r100001011 (combine-to-int 2 139)))
    )
  )