I've been playing around with rewriting some Java code in Clojure and
did some simple benchmarking in the process. In this case, there's a
huge disparity in the performance numbers between the two languages,
and I'm wondering what the cause may be. The program rotates a string
from "aaaa", "aaab", ..., "zzzz". The Java version takes 0.77 seconds
to complete while the Clojure version takes 22 seconds. I've tried to
make the scripts relatively isomorphic and have verified that they
produce the same results. I'm pasting the source below.
tra...@travis-ubuntu:/tmp% time clj base26.clj
clj base26.clj 21.99s user 1.23s system 85% cpu 27.318 total
tra...@travis-ubuntu:/tmp% time java Base26
java Base26 0.77s user 0.04s system 78% cpu 1.029 total
clojure version:
(defn base26 [n]
(let [seed-string "aaaa"
s (new StringBuilder seed-string)]
(loop [pos (- (count seed-string) 1)
x n]
(if (> x 0)
(let [digit (+ (int \a) (mod x 26))]
(. s setCharAt pos (char digit))
(if (and (> pos 0) (> x 0))
(recur (- pos 1) (/ x 26))))))
(. s toString)))
(doseq [i (range (Math/pow 26 4))]
(base26 i))
java version:
import java.lang.StringBuilder;
public class Base26 {
public static void main(String[] args) {
for (int i = 0; i < Math.pow(26, 4); i++) {
Base26.base26(i);
}
}
public static String base26(int num) {
if (num < 0) {
throw new IllegalArgumentException("Only positive numbers
are supported");
}
StringBuilder s = new StringBuilder("aaaa");
for (int pos = 3; pos >= 0 && num > 0 ; pos--) {
char digit = (char) ('a' + num % 26);
s.setCharAt(pos, digit);
num = num / 26;
}
return s.toString();
}
}
I've tried warn-on-reflection, and it didn't report anything.
Thanks,
Travis
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