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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: One code is aggressively optimised, while another not. Why?
Date: Wed, 12 Jul 2017 10:07:15 +0200
Organization: Decebal Computing
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I am looking into some performance metrics. I have the following code:
    long sum = 0L;

    for (long i = start; i < end; ++i) {
        sum += i;
    }

And this code:
    long sum = 0L;

    for (int i = start; i < end; ++i) {
        sum += i;
    }

Start and end are defined like:
    private static int end   = Integer.MAX_VALUE;
    private static int start = Integer.MIN_VALUE;


The second code takes about 50% more time to execute. No surprise
there. But the first code is aggressively optimised when run several
times (the fifth run is about 2½ million times faster as the first
run), while the second code is not optimised:
    09:41:10: Timing long int
    09:41:10: took 2.08E+00 seconds.
    09:41:13: took 1.29E-03 seconds.
    09:41:13: took 1.25E-04 seconds.
    09:41:13: took 1.36E-06 seconds.
    09:41:13: took 7.97E-07 seconds.

    09:41:13: Timing long long
    09:41:13: took 3.09E+00 seconds.
    09:41:16: took 3.11E+00 seconds.
    09:41:19: took 4.03E+00 seconds.
    09:41:23: took 3.94E+00 seconds.
    09:41:27: took 3.87E+00 seconds.

Why the difference?

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof