Endianness and pointer casts are the mechanical part and I would expect Zig to emulate them correctly.

Other parts, like floats are harder. This is where a difference shows. Rust is like: "Sorry, since we cannot uphold our guarantees, no transcendentals for you at comptime ", whereas Zig is chill about that and let you have your transcendentals even if results may differ between comptime and runtime. Different mindsets.