fn swap_d(cpu: &mut Cpu) {
        let d = cpu.d();

        let r = swap(cpu, d);

        cpu.set_d(r);
    }
/// Swap low and high nibbles of `D`
Swap low and high nibbles of `D`
Swap low and high nibbles of ` D `
fn swap_d(cpu: &mut Cpu) {
        let d = cpu.d();
        let r = swap(cpu, d);
        cpu.set_d(r);
    }
fn swap_d ( cpu : & mut Cpu ) { let d = cpu . d ( ) ; let r = swap ( cpu , d ) ; cpu . set_d ( r ) ; }
Swap low and high nibbles of `D`
Swap low and high nibbles of ` D `
cpu
&mut Cpu
cpu
&mut Cpu