Array equality, comparison and mismatch (original) (raw)

Andrew Haley aph at redhat.com
Tue Oct 13 10:03:36 UTC 2015

On 13/10/15 10:22, Paul Sandoz wrote:

Analysis so far indicate big gains are to be had on larger arrays with better or no impact on small arrays if i do the following instead:

if (Double.doubleToRawLongBits(a[i]) != Double.doubleToRawLongBits(b[i])) { int c = Double.compare(a[i], b[i]); if (c != 0) return c; }

I was about to make a similar comment. My experiment was with

    if (Double.doubleToRawLongBits(a[i]) != Double.doubleToRawLongBits(b[i])
            && (Double.doubleToLongBits(a[i]) !=
                Double.doubleToLongBits(b[i])))
            return Double.compare(a[i], b[i]);
    }

which is about twice as fast as the original version, as is yours. But yours is more elegant. :-)

It's a shame that HotSpot doesn't see through the load of a double and then the conversion through doubleToRawLongBits: it could just load directly into the integer registers.

Andrew.

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