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.

• Have fun.
• Learn about WebAssembly features (SIMD, threads, etc.)
• Small WASM file.
• Low memory usage.
• Fast execution time.

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

npm install -g wat-wasm
wat2wasm <WAT_FILE> <FEATURES...>

For the list of required features, see below.

The table below lists non-trivial data structures and algorithms used in each solution.

• 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.shuffle syntax. It takes 2 v128s (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.