Clojure Integer Overflow Using reduce function

Question

Unfortunately my code is giving me an Integer Overflow exception.

(defn even-fib-sum [n]
   (reduce + 
      (filter even? 
         (take n (map first (iterate (fn [[x y]] [y (+ x y)]) [0 1]))))))

The problem occurs when I call the function and pass the value 4000000

(even-fib-sum 4000000) -> throws exception

(even-fib-sum 40) -> 82790070

cfrick · Accepted Answer · 2015-01-01 22:42:51Z

7

use +' instead of + to get auto promoting addition to bigintegers

(reduce +' 
   (filter even? 
     (take n (map first (iterate (fn [[x y]] [y (+' x y)]) [0 1])))))

Cloujure uses longs by default and treats overflow as an error. In the very early days of the language auto-promotion was the default until it was generally agreed that overflowing a long was almost always a bug except in the cases where people explicitly know they want it so it was changed and the +', *', and -' operators where added for the cases where people explicitly choose them

edited Jan 1, 2015 at 22:42

cfrick

37.3k7 gold badges61 silver badges76 bronze badges

answered Dec 30, 2014 at 23:58

Arthur Ulfeldt

91.7k30 gold badges205 silver badges285 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Bob Jarvis - Слава Україні Over a year ago

I believe that +' should be used in the last line of the function as well; otherwise it overflows at (even-fib-sum 93).

Collectives™ on Stack Overflow

Clojure Integer Overflow Using reduce function

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related