Awesome
🎄 Advent of WASM 2024
My Advent of Code 2024 solutions in hand-crafted WebAssembly. No processing in JavaScript‒input is copied to WebAssembly and the answer is computed entirely in there.
🎯 Goals
- Have fun.
- Learn about WebAssembly features (SIMD, threads, etc.)
- Small WASM file.
- Low memory usage.
- Fast execution time.
🧩 How to use
node index.js <DAY> <PART>
For help info, try node index.js.
When running with the input, the data reported includes:
- Average runtime in nanoseconds (one billionth of a second) and microseconds (one millionth of a second)
- Best runtime (in 100 iterations)
- WASM memory usage (excluding the input) in bytes
- Compiled WASM file size in bytes
⚙️ Compile
npm install -g wat-wasm
wat2wasm <WAT_FILE> <FEATURES...>
For the list of required features, see below.
| Day | Part | --simd |
|---|---|---|
| 1 | 1 | ✅ |
| 1 | 2 | |
| 2 | 1 | |
| 3 | 1 | |
| 3 | 2 | |
| 4 | 1 | |
| 4 | 2 |
📝 Reports
| Day | Part | Best runtime (μs) | WASM mem usage (bytes) | WASM file size (bytes) |
|---|---|---|---|---|
| 1 | 1 | 311.006 | 8000 | 473 |
| 1 | 2 | 507.89 | 8000 | 317 |
| 2 | 1 | 41.836 | 0 | 247 |
| 3 | 1 | 28.495 | 0 | 645 |
| 3 | 2 | 43.931 | 0 | 915 |
| 4 | 1 | 242.491 | 19861 | 552 |
| 4 | 2 | 109.441 | 0 | 274 |
🍫 Data structures and algorithms
The table below lists non-trivial data structures and algorithms used in each solution.
| Day | Part | Data structures | Algorithms |
|---|---|---|---|
| 1 | 1 | Array | Insertion sort |
| 1 | 2 | Array | |
| 2 | 1 | ||
| 3 | 1 | Finite state automaton | |
| 3 | 2 | Finite state automaton | |
| 4 | 1 | Array | Transposition |
| 4 | 2 |
📔 Diary
Day 1
- WebAssembly uses little-endianess. If the input is processed at a less nuanced level than byte-by-byte, then we will have to be careful how the input is written to WebAssembly memory.
- Switching to SIMD didn't improve performance by much. I'm surprised to have got it working on first try though.
- Took me a while to learn
i8x16.shufflesyntax. It takes 2v128s (on the stack) and 16 0-based indices, which indexes into bytes stored in the two vectors. The returned vector is formed from the bytes pointed to by the indices.