Function exec_alu

crates/virtual-machine/src/cpu/pipeline/execute.rs:425–471

(
    funct3: u8,
    funct7: u8,
    rd: usize,
    rs1: usize,
    rs2: usize,
    regs: &Registers,
    pc: u64,
)

}

fn exec_alu(
    funct3: u8,
    funct7: u8,
    rd: usize,
    rs1: usize,
    rs2: usize,
    regs: &Registers,
    pc: u64,
) -> Result<ExecResult, VmError> {
    let a = regs.read_x(rs1);
    let b = regs.read_x(rs2);
    let result = match funct7 {
        0x00 => match funct3 {
            0 => alu::add(a, b),
            1 => alu::sll(a, b),
            2 => alu::slt(a, b),
            3 => alu::sltu(a, b),
            4 => alu::xor(a, b),
            5 => alu::srl(a, b),
            6 => alu::or(a, b),
            7 => alu::and(a, b),
            _ => return Err(VmError::IllegalInstruction(funct3 as u32)),
        },
        0x20 => match funct3 {
            0 => alu::sub(a, b),
            5 => alu::sra(a, b),
            _ => return Err(VmError::IllegalInstruction(funct3 as u32)),
        },
        0x01 => match funct3 {
            0 => alu::mul(a, b),
            1 => alu::mulh(a, b),
            2 => alu::mulhsu(a, b),
            3 => alu::mulhu(a, b),
            4 => alu::div(a, b),
            5 => alu::divu(a, b),
            6 => alu::rem(a, b),
            7 => alu::remu(a, b),
            _ => return Err(VmError::IllegalInstruction(funct3 as u32)),
        },
        _ => return Err(VmError::IllegalInstruction(funct7 as u32)),
    };
    Ok(ExecResult::WriteInt {
        rd,
        val: result,
        next_pc: pc.wrapping_add(4),
    })
}

fn exec_alu32(
    funct3: u8,