Macro shuffle 

macro_rules! shuffle {
    (xor, $value:expr, $offset:expr, $width:expr) => { ... };
    (up, $value:expr, $offset:expr, $width:expr) => { ... };
    (down, $value:expr, $offset:expr, $width:expr) => { ... };
    (idx, $value:expr, $offset:expr, $width:expr) => { ... };
}

define a macro to use shuffle with a specific mode xor, up, down.