Monthly Archives: July 2017

Explicit Intent and Even Faster Hash Codes

I wrote a post recently about how disappointed I was that the optimiser couldn’t outsmart some clever Java code for computing hash codes. Well, here’s a faster hash code along the same lines. The hash code implemented in Arrays.hashCode is a polynomial hash, it applies to any data type with a positional interpretation. It takes

Still True in Java 9: Handwritten Hash Codes are Faster

One of the things to keep in mind with Java is that the best performance advice for one version may not apply to the next. The JVM has an optimiser which works by detecting intent in byte-code; it does a better job when the programmer is skilled enough to make that intent clear. There have

New Methods in Java 9: Math.fma and Arrays.mismatch

There are two noteworthy new methods in Java 9: Arrays.mismatch and Math.fma. Arrays.mismatch This method takes two primitive arrays, and returns the index of the first differing values. This effectively computes the longest common prefix of the two arrays. This is really quite useful, mostly for text processing but also for Bioinformatics (protein sequencing and