Function addi

crates/virtual-machine/tests/vm_pipeline.rs:45–48

addi rd, rs1, imm -> opcode=0x13, funct3=0

(rd: u32, rs1: u32, imm: i32)

// addi rd, rs1, imm  -> opcode=0x13, funct3=0
fn addi(rd: u32, rs1: u32, imm: i32) -> u32 {
    let imm12 = (imm as u32) & 0xFFF;
    (imm12 << 20) | (rs1 << 15) | (rd << 7) | 0x13
}

// add rd, rs1, rs2  -> opcode=0x33, funct3=0, funct7=0
fn add(rd: u32, rs1: u32, rs2: u32) -> u32 {