compilers

A long period since my last post indicates that a lot has happened. My son Adam was born on January 11th at about 3 a.m. He's changing a lot, already smiles, speaks various vowels and tries to catch objects and hold them in his hand. It's a great experience to be a father, although it requires a lot of patience. Well, it's never a bad time to learn something new, and I personally find it very inspiring :).

In the meantime I released an update for WebIssues, changed the layout of my web sites a bit and also made some improvements of Saladin (you can expect a new version soon). I also made a pretty good progress with my novel. I will write more about it shortly, but it's generally a story about hackers, magic and virtual worlds. The nature of my day job is rather destructive for my imagination (and for the amount of time I can spend on other things), but it turns out that I'm still able to use it and I have some interesting ideas from time to time.

I'm also very proud that after so many years I successfully revived the idea of Descend. In a nutshell, it's the successor of a program for drawing parametric surfaces which I wrote over 10 years ago. Last year I wrote an adaptive tessellator and I made a working prototype of the program using Qt's built-in JavaScript engine. It worked nicely, but it wasn't very fast. Qt uses the JavaScriptCore engine from WebKit, which is currently developed by Apple and powers the Safari browser. It is one of the fastest JS engines, with a register based vritual machine and built-in JIT compiler (you can find more interesting information about it in this post). However, JavaScript is an object oriented, dynamically typed language, best suited for creating complex AJAX-based applications. It's not optimized for number crunching.

So I designed my own language, which is statically typed and has only four types: boolean, float, 4D vector and 4x4 matrix. I called it Misc, although it doesn't have much to do with the old Misc engine that I wrote 7 years ago (which was dynamically typed and supported complex types like objects and arrays). I wrote a relatively simple compiler which produces bytecode and doesn't perform any fancy optimizations, and a stack based virtual machine with dedicated instructions for vector and matrix operations, trigonometric functions, etc. As soon as I got it working, I performed some benchmarks.

I created three versions of Descend: one based on JavaScriptCore, another one using the new Misc engine, and the third one with equations hard-coded in C++. All three versions were compiled using Visual C++ 2008 with full optimizations and link-time code generation. I measured the total time of generating a deformed sphere which consisted of 43,000 vertices and required calculating 135,000 samples (the tesselator needs 3 samples per vertex in order to accurately calculate normal vectors).

The results are very encouraging: the version using Misc is not only 5 times faster than the one based on JavaScriptCore, but also just 3.5 times slower than the one using native code! Obviously this doesn't mean that Misc code is almost as fast as native code, but the overhead added by the Misc interpreter is not very big, compared to the cost of the tessellator itself and the cost of calculating the trigonometric functions (which is the same for all three versions). In contrast, the overhead of JavaScriptCore is much more noticeable.

Surely there's still some room for improvement, but I doubt I would be able to squeeze more than a few CPU cycles without making the code significantly more complex. So I'd rather start working on the UI to make it possible to draw something more than a single surface. I will publish the first version once it's usable, which may take a few months depending on how much time I will be able to dedicate to it.