GameBoy\Opcode::opcode13 PHP Method

    public static function opcode13(Core $core)
    {
        $core->registerC = $core->unsbtub($core->registerC - 1);
        $core->FZero = $core->registerC == 0;
        $core->FHalfCarry = ($core->registerC & 0xf) == 0xf;
        $core->FSubtract = true;
    }