3 ms·

The Three Byte Fix

59 points by breck 3y ago

mucle6 3y ago
Does anyone have tips for how to navigate new code bases faster? I feel like I would have given up reading through the code before I found the issue discussed in the article I didn't read through the code but maybe the library was small and this was just a case of checking the difference between c++ and js by line for 1k lines or something
- markerz 3y ago
  There’s plenty of strategies. In this case, if you can see two code based behaviors have diverged, just run both through a step by step debugger and see where they diverge. Or if you run both through a profiler, you can see what segment of code is taking a crazy amount of time in comparison. In general, narrowing down what you’re looking at is the goal. In this case, a big hint is that the code should be O(nlogn) but is actually O(n^2) which is a huge hint that we’re in a nested loop and the break condition isn’t getting triggered properly. I would have looked closely at the loops because of this. The code itself is ~400 lines long minus a bunch of comments. This feels very approachable to skim through in an hour. I also love creating new variables and naming them what I’m learning. Often times naming things will make bugs very obvious.
  - euroderf 3y ago
    > I also love creating new variables and naming them what I’m learning. Often times naming things will make bugs very obvious. Agreed. There should be a formalish name for this technique/style.
lilyball 3y ago
> I was amazed by how fast he found that bug in code he had never seen before. I'm not sure if he read carefully through the original paper or came up with the clever debug strategy of "since this is a port, let's compare to the original, looking for typos, with a particular focus on the loops". The latter is exactly what I would have done. If the algorithm did not match the expected complexity, the most likely reason is a bug in the implementation, and the quickest way to find that bug is to compare it with a known-good implementation, such as the one that the code was ported from.
jeffrallen 3y ago
Neves' Law strikes again.

59 points by breck 3y ago

Does anyone have tips for how to navigate new code bases faster? I feel like I would have given up reading through the code before I found the issue discussed in the article I didn't read through the code but maybe the library was small and this was just a case of checking the difference between c++ and js by line for 1k lines or something

markerz 3y ago
There’s plenty of strategies. In this case, if you can see two code based behaviors have diverged, just run both through a step by step debugger and see where they diverge. Or if you run both through a profiler, you can see what segment of code is taking a crazy amount of time in comparison. In general, narrowing down what you’re looking at is the goal. In this case, a big hint is that the code should be O(nlogn) but is actually O(n^2) which is a huge hint that we’re in a nested loop and the break condition isn’t getting triggered properly. I would have looked closely at the loops because of this. The code itself is ~400 lines long minus a bunch of comments. This feels very approachable to skim through in an hour. I also love creating new variables and naming them what I’m learning. Often times naming things will make bugs very obvious.
- euroderf 3y ago
  > I also love creating new variables and naming them what I’m learning. Often times naming things will make bugs very obvious. Agreed. There should be a formalish name for this technique/style.

lilyball 3y ago

> I was amazed by how fast he found that bug in code he had never seen before. I'm not sure if he read carefully through the original paper or came up with the clever debug strategy of "since this is a port, let's compare to the original, looking for typos, with a particular focus on the loops". The latter is exactly what I would have done. If the algorithm did not match the expected complexity, the most likely reason is a bug in the implementation, and the quickest way to find that bug is to compare it with a known-good implementation, such as the one that the code was ported from.

jeffrallen 3y ago

Neves' Law strikes again.