September 8, 2008

Generating .DLL Wrappers

Filed under: cplusplus,Programming,Win32 — floodyberry @ 5:25 am
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A while ago I came across Create your Proxy DLLs automatically by Michael Chourdakis. I thought it was a good idea, but had some room for improvement:

  • Having to use an external .exe (dumpbin/tdump) was an unnecessary step, all the information you need is in the PE header!
  • He did not handle wrapping mangled names or forwarding forwards.
  • Generating an actual project instead of a command line compile call would be a lot more useful considering you will want to do some actual coding instead of generating an empty wrapper.
  • His coding style was somewhat awkward and not easy to modify.

With this in mind, I set about writing my own version. (more…)


July 9, 2008

The id Tech 4 Script Compiler Sucks Hard!

Filed under: Games,Optimization,Programming — floodyberry @ 3:23 pm
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Whoever did most of the work on the id Tech 4 Script Compiler, I’m calling you out! I’ll grant that you managed to write a major component of a successful commercial engine, but… it’s just so bad. What confounds me even more is that all of the engines after DooM III did almost nothing (effective) to try and fix it: If you check out the Quake IV, Prey, and ET:QW SDKs, they all have the same basic compiler with a couple things bolted on. The ET:QW guys did do a bit of work on it and tried to speed it up a bit, but “glacially slow” doesn’t seem like much of an improvement on “geologically slow”.

I first noticed how bad it was when I was doing the ET:QW -> Tribes stuff and started playing around with the scripts. Being so use to Tribes style scripting, two things hit me right off:

  1. You have to exit the mission and recompile every script if you want to update a script you just edited. Ok, pretty annoying, but I’m just playing around so it should get easier.
  2. On my AMD64 3200+, recompiling was “damn slow” (~20 seconds) in Release mode and “I’m going to read a book” (~60 seconds) in Debug. Issue #1 just got a lot more annoying.

How did they manage to develop on this for longer than 10 minutes before going crazy, let alone create an entire game? Apparently I was the first to get fed up enough about it, so I went to check out the compiler and see if I could find any hot spots.


February 15, 2008

Writing a (Tribes 1) Master Server

Filed under: Games,Programming,Tribes — floodyberry @ 10:59 am
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While I wrote this in September 2007, for various reasons I did not get around to putting the finishing touches on it. Please pretend you’re reading it then and not now!

After the hubbub over Sierra’s announcement that they were ceasing multiplayer support for Tribes 1 and the resulting scramble to locate a replacement master server, I decided to give a shot at writing one. The required feature set appeared simple enough to only take a week or so to implement but with enough gotchas to keep it suitably interesting. While I only had a vague idea of what was required, I got a jump start on proper design by finding Half-Life and Team Fortress Networking: Closing the Loop on Scalable Network Gaming Backend Services by Yahn W. Bernier, an article detailing the design, implementation, and potential problems of the Half Life master server. Even though some of the topics did not apply to the Tribes 1 requirements, e.g. I can’t alter the client’s behavior to auto rate-limit the server list transmission, the article was still quite valuable and an interesting read even if you aren’t implementing a master server. (more…)

May 17, 2007

C++ Templates and Class Inheritance

Filed under: cplusplus,Programming — floodyberry @ 1:03 am
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The following code is not legal C++:

template < class type >
struct A {
	void f() {}
	type mX;

template < class type >
struct B : public A<type> {
	void g() { mY = ( mX ); f(); }
	type mY;

The best part is that unless you know the obscure reason why it is not legal, it appears legal and might even compile and run perfectly depending on which compiler you’re using. Not surprisingly, that is exactly how I ran in to it. I was doing templated class inheritance and thought I was in the clear because everything ran fine with MSVC7.1 and ICC 9, but when I belatedly tried to compile with g++ 3.4.4, I ran in to the following errors: (more…)

April 14, 2007

UTF-8 Conversion Tricks

Filed under: cplusplus,Optimization,Programming — floodyberry @ 3:04 am
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UTF-8 is a wonderfully simple encoding format with some very nice properties, but the juggling required to convert to UTF-16, and UTF-32 can be a little tricky and fairly easy to do poorly. This is further compounded by the various error conditions you must keep an eye out for, such as overlong encodings, reserved ranges, surrogate markers, incomplete sequences, and so on.

These are a couple tricks you can employ to hopefully keep the conversion fast and robust.


March 29, 2007

Breaking SuperFastHash

Filed under: Hashing,Programming,Security — floodyberry @ 3:31 am
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After the problems SuperFastHash had in Hash Algorithm Attacks, I decided to try and break it completely, i.e. generate collisions algorithmically instead of brute forcing them. The attempt was more successful than I had anticipated, although Paul is obviously aware of the weak mixing in the final bits as evidenced by his comment in the source code, “Force ‘avalanching’ of final 127 bits”. My favorite collisions encountered would have to be “10/4 < 3”, “10/5 = 2”, and “10/6 > 1”, which have the property of hashing to the same value while being mathematically correct!

As I was writing this, I came up with a way to attack Bob Jenkins’ lookup3 as well. Unlike SuperFastHash, the lookup3 attack is due to the way the input bytes are being read in and does not indicate a deficiency in the mixing itself. If you are using lookup3 with hash tables, the core function will still be quite safe; it will only need to be modified if you are using it to generate unique 64bit identifiers and the input data could be altered for a malicious purpose.

With that said, let’s look at the attacks:


March 7, 2007

When Bad Hashing Means Good Caching

Filed under: Hashing,Programming — floodyberry @ 1:54 pm

I was testing various string hashing algorithms on chained hash tables, primarily to look at the bucket distribution and number of key comparisons with both prime and power of 2 sized tables. Each table node was set up to remember it’s full hash value so bucket collisions would only drop to a key comparison on a true key collision. I initially wasn’t concerned with run times, but I tacked on a timer anyway so I could get a quick metric on how collisions and distribution were affecting performance and wound up running in to a rather odd situation. (more…)

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