macro.clj

;; Okay, here's some practice. This might be a good candidate for a macro.

(defn little-int
  "Converts four input bits to an int, in little endian format."
  [b0 b1 b2 b3]
  (bit-or
   (bit-shift-left b3 24)
   (bit-or
    (bit-shift-left (bit-and b2 0xff) 16)
    (bit-or
     (bit-shift-left (bit-and b1 0xff) 8)
     (bit-and b0 0xff)))))

(defn little-long
  "Converts eight input bits to a long, in little endian format."
  [b0 b1 b2 b3 b4 b5 b6 b7]
  (bit-or
   (bit-shift-left b7 56)
   (bit-or
    (bit-shift-left (bit-and b6 0xff) 48)
    (bit-or
     (bit-shift-left (bit-and b5 0xff) 40)
     (bit-or
      (bit-shift-left (bit-and b4 0xff) 32)
      (bit-or
       (bit-shift-left (bit-and b3 0xff) 24)
       (bit-or
        (bit-shift-left (bit-and b2 0xff) 16)
        (bit-or
         (bit-shift-left (bit-and b1 0xff) 8)
         (bit-and b0 0xff)))))))))


(defn flipped-endian-float
  "Flips the endian order of the supplied byte sequence, and converts it to float."
  [bitseq]
  (->> bitseq
       (map-indexed (fn [idx bit]
                      (bit-shift-left
                       (bit-and bit 0xff)
                       (* 8 idx))))
       (reduce +)
       (Float/intBitsToFloat)))

;; same as above, with commas to show where the previous expression is threaded in.
(defn flipped-endian-float
  "Flips the endian order of the supplied byte sequence, and converts it to float."
  [bitseq]
  (->> bitseq
       (map-indexed (fn [idx bit]
                      (bit-shift-left
                       (bit-and bit 0xff)
                       (* 8 idx))) ,,,)
       (reduce + ,,,)
       (Float/intBitsToFloat ,,,)))


;; unthreaded version
(defn flipped-endian-float
  "Flips the endian order of the supplied byte sequence, and converts
  the sequence into a float."
  [bitseq]
  (Float/intBitsToFloat
   (reduce + (map-indexed (fn [idx bit]
                            (bit-shift-left
                             (bit-and bit 0xff)
                             (* 8 idx)))
                          bitseq))))