Simon Tatham's Home Page

Welcome to my web site. I'm Simon Tatham, a software engineer and free-software author in Cambridge, UK.

Here are links to the various other pages of this site.

• About me: some idea of who I am.
• Free software I've written, which you can download.
  • PuTTY: an SSH client for Windows, also able to talk to serial ports and speak older insecure protocols like Telnet.
  • A collection of GUI puzzle games, portable to many platforms: provided on the web in Javascript, downloadable versions for Windows and Unix, and third-party ports to various mobile devices.
  • spigot: a command-line exact real calculator.
  • Halibut: a documentation system with simple syntax and multiple output formats, used for the manuals of most of my software.
  • agedu: a Unix utility for tracking down where you're wasting disk space, by making it easy to spot large amounts of data with last-access times a long time ago.
  • IPBT: a Unix curses application which plays back ttyrec files with precision rewind capability.
  • xtruss: an X11 protocol tracing utility.
  • A collection of miscellaneous Unix utilities.
  • Gonville, an alternative font of musical symbols for use with GNU Lilypond.
  • Tweak: a Unix curses-based hex editor designed for highly scalable performance.
  • DoIt: a utility to allow a Unix machine to open documents on a Windows machine (for example, sending commands back to your Windows desktop machine from a Unix server you've connected to from there).
  • WinURL: a Windows utility to pull text out of the clipboard and launch it as a URL at the touch of a hot-key.
  • There are a few other things I've written which I'm now considering more or less unmaintained. See my unmaintained software page.
• My algorithms collection: some neat algorithms that aren't in common use.
• Mathematical sorts of things. (Many of these pages include some downloadable software so you can play with them yourself.)
  • A series of articles about generating aperiodic tilings in software using string-processing algorithms:
    • Part 1: recursive algorithms for walking around Penrose tilings and the hat tiling discovered in March 2023.
    • Part 2: same thing for the Spectre tiling discovered in May 2023.
    • Part 3: replacing the recursion in the previous articles with a finite state machine, slightly improving efficiency and eliminating a failure case.
    • Part 4: further improving the state-machine construction algorithm, and exploring various special instances of the tilings.
    • Part 5: an algorithm for dealing with a tiling substitution system which you can't build an efficient state machine for, by refining it into one you can.
  • A solution to the impossible Solitaire Army problem (by cheating, of course – making an infinite number of moves).
  • A few HTML5 web toys demonstrating mathematical things:
    • Lagrange's polynomial interpolation formula
    • the Gauss-Lucas theorem
    • composing Möbius maps to make a constant multiplication
    • the fractal you get by plotting all roots of complex polynomials with coefficients in a finite set
  • A small software project from decades ago: constructing polyhedra from repelling points on a sphere. More frivolously, I reused the same software to print some nets of polyhedra with pictures on their surfaces.
• Some selected articles and essays:
  • How to Report Bugs Effectively: a general article on how to send a programmer a bug report which will actually help them fix the problem.
  • How to Read Error Messages: a guide to getting the most out of typical kinds of error message you see from software, over and above "something went wrong".
  • A loose trilogy of articles about coroutines, because I'm a great fan of them:
    • Coroutines in C: an implementation of coroutines in portable ISO C, by a similar technique to Duff's device plus some C preprocessor abuse.
    • Writing custom C++20 coroutine systems: an exposition of the C++20 coroutine mechanism and how to use it and customise it.
    • Philosophy of coroutines: a more general article discussing what coroutines are good for and how to get the most out of them.
  • Metaprogramming custom control structures in C: another piece of C preprocessor abuse to let you build quite general user-defined looping constructs alongside C's basic for and while.
  • The Descent to C: an introduction to C for people coming to it from higher-level languages, intended to warn you in advance about the likely culture shocks.
  • My personal FAQ about the fact that I have no sense of smell.
• More assorted articles, organised into a kind of quasi-blog.

I'm on Mastodon as @simontatham@hachyderm.io.