Open source projects

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I've been involved in building open source software since the early 90s. Unfortunately I can't find links for some of them, but here are ones for which I do.


This one was a programming challenge at r3 to build some software to identify solutions to the "Countdown" numbers game as quickly as possible. The idea of the game is to take 6 randonly chosen numbers from a set of 24 available numbers (1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 25, 50, 75, 100) and find a way to get to a larger random number in the range of 100 to 999, using only simple addition, subtraction, multiplication, and division.

I wrote this one in C++ and spent a few hours coming up with ways to shrink the problem search space: It's pretty quick but I never attempted to tune it to the instruction level!


c8 is a high performance arbitrary precision natural numbers, integers, and rational numbers library written in "modern" C++. The git repo is here: There's also a project wiki here:

When I built this code I also tracked the development journey on the wiki. This includes all my notes on how I was performance tuning things, down to the machine instruction level in many cases:

gcc (Ubicom processor backends)

From 2001 to 2012 I maintained the backends for Ubicom's IP2k and Ubicom32 processor family versions of gcc. I no longer have links for the IP2k version, but the 32-bit Ubicom32 version can be found here:

The Ubicom32 processor family was very unusual. All versions were heavily multithreaded (between 8 and 12 threads), executing in a single pipeline. Threads were interlaced so each instruction could be operating on a separate thread context. Used carefully this could make things incredibly efficient as most pipeline hazards could be hidden by other threads. The ISA was also very unusual in that it supported a memory-to-memory architecture where many instructions could include 2 memory references in a single 32-bit RISC instruction.


Liquorice was a very small operating system and IPv4 network stack, written entirely from scratch. It was designed to run on 8-bit Atmel AVR and 32-bit x86 processors.

The project ran through much of 2000, but I stopped working on the public version when I joined Ubicomat the end of 2000. The project evolved as a commercial operating system and network stack called ipOS. While ipOS started out very similar to Liquorice, it quickly diverged as we simplified concepts eliminated the software threading, and implemented much better design patterns to support some of the networking. Liquorice has some interesting ideas, and is a very small IP stack:


VSTa (short for Valencia's Simple Tasker) was a self-hosting microkernel operating system build in the 1990s. It had a lot of novel ideas, a simple and elegant kernel, and featured user-space device drivers and filesystems. Unusually, it also had a kernel debugger so if anythign went wrong it would drop into the debugger instead of just giving a kernel panic message.

It had a services model inspired by Plan 9, and had a largely complete GNU toolchain so it was capable of building itself. I was largely active in updating libc, porting tools, writing drivers, and performance tuning the kernel form 1993 to 1995

Andy Valencia (the guy behind the project) has an archive of the code and the mailing lists here:

mkdosfs (Linux)

I wrote the first 2 versions of mkdosfs back in 1993 and 1994. Eventually other maintainers folded this into the dosfstools repo, and can be found here (my original notes are in the change logs):