added sequence of non-squares

I'm just wondering if the fact that (1.9f32 as u32) is being truncated to 1 instead of rounded to 2 is set in stone as part of the spec or an implementation detail that may change in the future?
[The manual is not very expansive on how casts are supposed to work](http://doc.rust-lang.org/rust.html#type-cast-expressions) when they lose information...