SIMD support in Rust is still very early and required unsafe mode for SSE, and lepton makes heavy use of SSE intrinsics.

Now I do see http://huonw.github.io/simd/simd/ was being developed in August 2015, but it seems to be gathering dust of late.

I really do wish that Rust would provide nice alignment guarantees (eg 32 byte) without depending on customizing the allocator, and builtin, safe, SIMD instructions