> You could try adapting ...

Do you accept PRs for the Rust benchmarks? My code is nowhere near competitive to the Wuffs implementation, but it would be a fun goal to work towards.

> Note that statements like ... can silently overflow a u32

Thank you for catching that, I'll go through the entire codebase and try to fix those up.

That's a part of Rust that always makes me feel uneasy - the compiler will tell you if you're doing math with numbers of different bit widths, but it won't warn you in most cases about overflow. That would be a good addition to the Rust compiler, or at least a Clippy lint.