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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Four-bit-adder/Common-Lisp/four-bit-adder.lisp Normal file
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;; returns a list of bits: '(sum carry)
(defun half-adder (a b)
(list (logxor a b) (logand a b)))
;; returns a list of bits: '(sum, carry)
(defun full-adder (a b c-in)
(let*
((h1 (half-adder c-in a))
(h2 (half-adder (first h1) b)))
(list (first h2) (logior (second h1) (second h2)))))
;; a and b are lists of 4 bits each
(defun 4-bit-adder (a b)
(let*
((add-1 (full-adder (fourth a) (fourth b) 0))
(add-2 (full-adder (third a) (third b) (second add-1)))
(add-3 (full-adder (second a) (second b) (second add-2)))
(add-4 (full-adder (first a) (first b) (second add-3))))
(list
(list (first add-4) (first add-3) (first add-2) (first add-1))
(second add-4))))
(defun main ()
(print (4-bit-adder (list 0 0 0 0) (list 0 0 0 0))) ;; '(0 0 0 0) and 0
(print (4-bit-adder (list 0 0 0 0) (list 1 1 1 1))) ;; '(1 1 1 1) and 0
(print (4-bit-adder (list 1 1 1 1) (list 0 0 0 0))) ;; '(1 1 1 1) and 0
(print (4-bit-adder (list 0 1 0 1) (list 1 1 0 0))) ;; '(0 0 0 1) and 1
(print (4-bit-adder (list 1 1 1 1) (list 1 1 1 1))) ;; '(1 1 1 0) and 1
(print (4-bit-adder (list 1 0 1 0) (list 0 1 0 1))) ;; '(1 1 1 1) and 0
)
(main)