Retro Programming

Xorshift is a simple, fast pseudorandom number generator developed by George Marsaglia. The generator combines three xorshift operations where a number is exclusive-ored with a shifted copy of itself:
There are 60 shift triplets with the maximum period 216-1. Four triplets pass a series of lightweight randomness tests including randomly plotting various n × n matrices using the high bits, low bits, reversed bits, etc. These are: 6, 7, 13; 7, 9, 8...

A project I'm working on needs a fast square root but I couldn't find anything suitable online. After implementing several versions of the bit-by-bit algorithm I discovered the following code is particularly efficient when unrolled:
First Make It Work...

Recently I've entered a few of the programming challenges in the BASIC on the ZX Spectrum group on Facebook. They vary in difficultly but it's possible to write a program for most in under 30 minutes. If you're looking for a quick challenge or the opportunity...

A flood fill is a graphical algorithm to colour an area of screen bounded by pixels of another colour. The scanline technique is a fast, stack-efficient flood fill which can be implemented in 99 bytes of Z80, as demonstrated below: