I read this article and I know it’s written in English, but I’ve accepted defeat in trying to understand it.
I write code for a living and I’m doing my best to ignore the feelings of inadequacy I’m currently experiencing.
I am still in awe of the fast inverse square root method used in QuakeIII. Good times.
Blooper@lemmynsfw.com 3 days ago
xavier666@lemm.ee 3 days ago
but I’ve accepted defeat in trying to understand it
I may have shared the link but even I don’t know how it how it works.
It’s like admiring the Eiffel Tower; you can understand that it’s a marvel of engineering without understanding the underlying engineering concepts. Such experiences are rare but they truly humble you.
Regarding the square root, understand the following concepts
- Bit shifting simply shift the bits to a certain side (Left or right) =>
0010 << 1 → 0100 - Mathematically, it multiplies or divides the input number with a factor of 2, depending upon the type of shift
- If you shift the number
nwith a nice shift amountx(I have greatly greatly over-simplified this), then you can calculate the inverse sq. root since inverse square root is2^(-1/2) - Calculating the inverse square root manually will take lots of clock cycles, which was not feasible for a FPS game with the limited h/w
- Bit shifting is a lot faster since we are not computing, but instead shifting
The resultant shifting gives us an answer which is close enough to the answer, and that is good enough for FPS games for calculation of reflections.
PS: Someone who is more experienced in this domain can correct me if I’m wrong.
- Bit shifting simply shift the bits to a certain side (Left or right) =>
VindictiveJudge@lemmy.world 3 days ago
IIRC, someone got with the author of that bit of code to ask how they came up with it, but they had simply learned it from someone else. So they tracked them down and found that they had also learned it from someone else. They eventually landed on Greg Walsh as the original author, but for a bit the code had no known origin.