The motivating examples read like nonsense to me. (I don't really speak Rust, but I think I'm reading them correctly? I don't know.) They seem to be saying that 1 + 1,000,000 = 1,000,000; or 1 + 100,000,000 is 16,777,216? With no remark? That's not right even for 32-bit floats.
vec![1.0; 1_000_000_000] is Rust notation for an array that contains 1.0 one billion times. I can understand it's a bit confusing/frustrating if you're unfamiliar with Rust syntax, sorry.
