Well packed structs allow us to fit more data into the cache, letting us process more data, faster. This project aims to take a struct definition and visually present it so you can see how many bits are directly in use, and how many are being wasted.

JAM RESULTS

I got as far as being able to draw out a (relatively) arbitrary struct in such a way that padding was prepended to align any variable to its natural alignment/size, and added at the end to pad the struct out to its full alignment.

What Went Right?

• Choosing a palette from lospec.org! It's a little thing, but I liked having a relatively constrained palette to work with. It made me consider how few colours I could get away with and still communicate what I was trying to get across. While there's room for improvement, I was happy with where I got to.

• Relatively Constrained Target. I tried to keep the scope very small for this, knowing my time was limited through the jam. In terms of 'visualizing' something, I feel I got what I wanted to see relatively quickly.

What Went Wrong?

• Platform Choice
• Scope

I made this as a native macos program in jai, and had a blast doing so. But, my goal is to make it into a toy that you can play with and get a feel for what actually is happening under the hood with your memory layouts, rather than making a hard-core tool for getting in and optimizing things. To that end, perhaps making this a web-based tool that people could use like godbolt would have a larger impact for the community.

In terms of scope, I didn't hit what I wanted to in terms of interactivity - being able to drag the variables around, add and remove different ones of different sizes and playing to get that intuitive feel for memory layout I completely missed. I managed to start down that path, with some simple mouse over highlighting, but in terms of what I got done for the jam, it's absolutely bare bones.

LOOKING AHEAD

I solidified my understanding of structs and their eventual layouts a lot in the process of making this, and I feel there's further I can go down this path. At the very least, I want to:

• Add drag/drop reordering
• Add & Remove variables
• Be able to paste in a struct so you can take parts of your program and see if you can optimize them visually.

The other thing I'd like to display is how well a given struct fits into cache lines. 'If you had a flat array of these, how many could you process before you had to hit a higher cache?' kind of thing.