Topic: -={ Challenge }=- Addition without Arithmetic Operators

[Lee Mac]

The Challenge:

Construct a function returning the sum of two integers without using the addition operator ("+").


I'll get the trivial one out of the way:

Code - Auto/Visual Lisp: [Select]

1. (defun _+ ( a b ) (- a (- b)))

Bonus points for originality 

[MP]

Doing this blind from my phone but this works in my hungover brain:

(apply '- (mapcar '- (list a b)))

[Lee Mac]

this works in my hungover brain:

(apply '- (mapcar '- (list a b)))

Indeed it does - nice variation MP

[MP]

Really, lol!!

This may work for positive ints:

Code: [Select]

(defun _+ ( a b / temp )
    (while (< 0 b)
        (setq
            temp (logand a b)
            a    (boole 6 a b)
            b    (lsh temp 1)
        )
    )
    a 
)
Fun challenge.

[Lee Mac]

This may work for positive ints:

Code: [Select]

(defun _+ ( a b / temp )
    (while (< 0 b)
        (setq
            temp (logand a b)
            a    (boole 6 a b)
            b    (lsh temp 1)
        )
    )
    a 
)

Very good MP! 

I'm glad you are enjoying the challenge!

Here's another bitwise approach, though processing the addition bit-by-bit (and should therefore work with negative ints also):

Code: [Select]

(defun _+ ( a b )
    (defun foo ( a b c / x y )
        (cond
            (   (= 0 a b) c)
            (   (setq x (boole 1 1 a)
                      y (boole 1 1 b)
                )
                (logior (boole 6 c (boole 6 x y))
                    (lsh
                        (foo
                            (lsh a -1)
                            (lsh b -1)
                            (logior
                                (boole 1 c x)
                                (boole 1 c y)
                                (boole 1 x y)
                            )
                        )
                        1
                    )
                )
            )
        )
    )
    (foo a b 0)
)

[Marc'Antonio Alessi]

Just an idea if a integer > 0:

Code: [Select]

(defun _+ (a b)
  (repeat a (setq b (1+ b)))
)Maybe it is a start for all conditions...

[Marc'Antonio Alessi]

Here is:

Code: [Select]

(defun _+ (a b)
  (if (> a 0)
    (repeat a (setq b (1+ b)))
    (repeat (abs a) (setq b (1- b)))
  )
)


[VovKa]

Code: [Select]

(defun _+ ( a b ) (distance (list 0 0) (polar (list a 0) 0 b)))for positive

oops i was dumb

Code: [Select]

(defun _+ ( a b ) (car (polar (list a 0) 0 b)))

[Lee Mac]

Here is:

Code: [Select]

(defun _+ (a b)
  (if (> a 0)
    (repeat a (setq b (1+ b)))
    (repeat (abs a) (setq b (1- b)))
  )
)


Nice one Marc 

oops i was dumb

Code: [Select]

(defun _+ ( a b ) (car (polar (list a 0) 0 b)))

Very original VovKa - excellent 

[Lee Mac]

A different route:

Code: [Select]

(defun _+ ( a b / r s )
    (if (setq s (vla-getinterfaceobject (vlax-get-acad-object) "scriptcontrol"))
        (progn
            (setq r
                (vl-catch-all-apply
                   '(lambda nil
                        (vlax-put-property s 'language "vbscript")
                        (vlax-invoke s 'eval (strcat (itoa a) "+" (itoa b)))
                    )
                )
            )
            (vlax-release-object s)
            (if (not (vl-catch-all-error-p r)) r)
        )
    )
)
EDIT: OK, So it doesn't quite meet the challenge criteria, but I'll keep it here for those spectating...

[Lee Mac]

Another simple math trick:

Code: [Select]

(defun _+ ( a b ) (log (* (exp a) (exp b))))

[Lee Mac]

Another variation on the trivial solution:

Code: [Select]

(defun _+ ( a b ) (- (1- a) (~ b)))

[MP]

Cool beans, nice job guys. :thumbsup:

[Stefan]

Code: [Select]

(defun _+ ( a b ) (car (polar (list a 0) 0 b)))

very nice vovka!

Another simple math trick:

Code: [Select]

(defun _+ ( a b ) (log (* (exp a) (exp b))))

I saw that, but I wasn't fast enough... Here is another math trick

Code - Auto/Visual Lisp: [Select]

1. (defun _+ (a b)
2.   (if (= a b)
3.       (* 2 a)
4.       (/ (- (* a a) (* b b)) (- a b))
5.   )
6. )

[Stefan]

Code - Auto/Visual Lisp: [Select]

1. (defun _+ (a b)
2.   (if (zerop a) b (* a (1+ (/ b a)))
3. )