Hacker News Reader

Comment by deletes | Hacker News Reader

Could you point out some relevant parts of the code for those not familiar with the codebase( there is a Lot of files ).

View on HN

I don't think this particular bit was in Doom, but there was the fast inverse square root trick[1] that is only a couple lines of code, yet has a very lengthy explanation that requires both knowledge of math and floating point representation.

[1] http://en.wikipedia.org/wiki/Fast_inverse_square_root

That was in Doom 3, to get the surface normals. That piece of code is also a hack since it breaks certain rules of c language.

I meant Quake 3 of course.

I think this may also a good example of why they say programmers don't need math. Very few people have the opportunity to even be in a position of inventing new algorithms like this. They are just going to read the relevant academic papers or use a library that implements it for them to make use of something like this in their own code. Even if you fully understand why the algorithm works, there is still a certain impostor syndrome at play for not being the one to invent it, leading people to believe they do not know math.

> They are just going to read the relevant academic papers

And how are you planning on doing that if you have no understanding of Maths?

The same way you can write an if statement without understanding of math. i.e. You can't, but we don't label it math, because it is not the invention of new mathematical concepts. Only people sitting in ivory towers doing things with math that the world has never seen before are considered to know math in the eyes of most programmers, it seems.

Not only that, but that bit of Q3 code was at one point in time a mystery to even John Carmack. Which is why it has the "what the fuck?" comment next to the magic number. Eventually they did track down the guy that authored that bit of code. Not only did the guy that wrote that have a good understanding of the math behind it, but he also understood the low-level mechanics of floating point. Which is something your average math major wouldn't know much about. Even most software engineers don't know floating point, sad as that may be.

But Doom and early Quake are bad examples of why math is needed. Those were ground-breaking games. Their math has been encapsulated and turned into libraries and things like DirectX and OpenGL. Today, you generally just take a physics engine and 3d engine off the shelf and tweak it a little here and there.

Reply on news.ycombinator.com