Macro avec

macro_rules! avec {
    () => { ... };
    ([$align: expr]| ) => { ... };
    ([$align: expr]| $elem: expr; $count: expr) => { ... };
    ([$align: expr]| $($elem: expr),*) => { ... };
    ($elem: expr; $count: expr) => { ... };
    ($($elem: expr),*) => { ... };
}

Create a vector that is aligned to a cache line boundary.