Function funct7

crates/virtual-machine/src/cpu/decoder.rs:885–887

(word: u32)

// I-type immediate: bits[31:20], sign-extended to 64 bits.
fn i_imm(word: u32) -> i64 {
    sign_ext(field(word, 31, 20), 12)
}

// U-type immediate: upper 20 bits placed at [31:12], lower 12 bits zero.
// We sign-extend from the 32-bit word so that large addresses work correctly.