Function core::hash::sip::u8to64_le

unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64

Loads a u64 using up to 7 bytes of a byte slice. It looks clumsy but the copy_nonoverlapping calls that occur (via load_int_le!) all have fixed sizes and avoid calling memcpy, which is good for speed.

Safety: this performs unchecked indexing of buf at start..start+len, so that must be in-bounds.