Question

Java.

I have a very small int array (4 elements).

What’s the fastest way to get max value? All values will be between 0 and 255.

Also int array is faster than byte array? Is casting much of a hit?

What’s the fastest way to get sum of all values?

The reason I ask is cause this is a major bottleneck in a program I inherited. They aren’t slow per say, but the guy is calling these methods many many times and it adds up. Eventually I need to rewrite the entire thing, but looking for some quick tricks to speed this up in the short term.

Answer 1

Here’s my go at it… basically an unrolled loop. The JIT would probably have recognized that a loop would have gone from 0 to 3 and unrolled it itself anyway, but who knows…

public static int max(int[] a) {
    int max = a[0] > a[1] ? a[0] : a[1];
    max = a[2] > max ? a[2] : max;
    return a[3] > max ? a[3] : max;
}

Sum would obviously just be a[0] + a[1] + a[2] + a[3].

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You could also try packing the four 0-255 values in an int, and do some bit-operations instead.