Anonymous user
Four bit adder: Difference between revisions
→{{header|Clojure}}
m (→{{header|Java}}: Changed variable name to reflect usage (fourBitAdder --> multiBitAdder)) |
|||
Line 611:
(n-bit-adder [true true true true true true] [true true true true true true])
=> (false true true true true true true)
----
;; Another solution in Clojure
(ns rosetta.fourbit)
;; a bit is represented as a boolean (true/false)
;; a word is a big-endian vector of bits [true false true true] = 11
;; multiple values are returned as vectors
(defn or-gate [a b]
(or a b))
(defn and-gate [a b]
(and a b))
(defn not-gate [a]
(not a))
(defn xor-gate [a b]
(or-gate (and-gate (not-gate a) b) (and-gate a (not-gate b))))
(defn half-adder [a b]
"result is [carry sum]"
(let [carry (and-gate a b)
sum (xor-gate a b)]
[carry sum]))
(defn full-adder [a b c0]
"result is [carry sum]"
(let [[ca sa] (half-adder c0 a)
[cb sb] (half-adder sa b)]
[(or-gate ca cb) sb]))
(defn nbit-adder [va vb]
"va and vb should be big endian bit vectors of the same size. The result
is a bit vector having one more bit (carry) than args."
{:pre [(= (count va) (count vb))]}
(let [[c sums] (reduce (fn [[carry sums] [a b]]
(let [[c s] (full-adder a b carry)]
[c (conj sums s)]))
;; initial value: false carry and an empty list of sums
[false ()]
;; rseq is constant-time reverse for vectors
(map vector (rseq va) (rseq vb)))]
(vec (conj sums c))))
(defn four-bit-adder [a4 a3 a2 a1 b4 b3 b2 b1]
"Returns [carry s4 s3 s2 s1]"
(nbit-adder [a4 a3 a2 a1] [b4 b3 b2 b1]))
(comment
(four-bit-adder false true true false true false true true)
;; [true false false false true]
)
</lang>
| |||