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> Floating point math is deterministic.

It is deterministic in a single machine, but it unfortunately is not deterministic across machines (and specially not across architectures)

... however, if you restrict yourself to a subset of floating point, it's straightforward to provide cross-platform determinism. That's what's the Rapier physics engine does

https://rapier.rs/docs/user_guides/rust/determinism/

On that note, Wasmtime has an option to enable NaN canonicalization, which should patch that hole, too: https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#...

It may also be thread nondeterminism, eg relying on the commutativity of addition etc.

The other common one is elementary functions from libm (i.e. exp/log etc)

Do note that sqrt should return the same results on all libm implementations, as well as functions like nextafter or scalbn.