Function lui 

pub const fn lui(imm: u16) -> u64

LUI — load upper immediate.

The 16-bit immediate is placed in bits 31..16 and the 32-bit result is then sign-extended, so a LUI of 0x8000 produces 0xFFFF_FFFF_8000_0000 rather than 0x0000_0000_8000_0000.