How do I avoid "ArithmeticException integer overflow" in Clojure?

Question

It seems to happen all the time. For example:

(apply * (range 1 101)) 

gives me the error

ArithmeticException integer overflow  clojure.lang.Numbers.throwIntOverflow (Numbers.java:1374) 

While in Ruby 1.9.2 the (conceptually) equivalent code,

(1..100).reduce(:*) 

produces the desired result of

93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000 

Obviously the two languages are quite different under the hood but it seems like they should both be able to handle this calculation without issue. Am I doing something wrong here? Or do I have an incorrect understanding?

Answer 1

You need to use some form of BigInteger.

Try (apply *' (range 1 101)).

(see http://dev.clojure.org/display/doc/Documentation+for+1.3+Numerics -- evidently this auto-promotes upon overflow?)

Answer 2

From Clojure 1.3, you should cast Integer(or Long) to BigInt explicitly, otherwise there will be "ArithmeticException integer overflow" error when the number is too large.

There are three solutions, please pick the one you favor:

• use one of the auto-promoting math functions:+', -', *', /', inc', dec'

  example: (apply *' (range 1 101))

• use the BigInt type cast function

  example: (apply * (range (bigint 1) 101))

• change to BigInt numeric literal

  example: (apply * (range 1N 101))

Reference: Documentation for Clojure 1.3 Numerics