Convert and mask bits of little endian to big endian

Question

I am working on a Qt/C++ application. I want to show state of 3 hall sensors so I read it from micro-controller this way:

uint8_t state = getState(whichMotor);
int numChars = sprintf(sBuff, "%d", state);
HAL_UART_Transmit_DMA(&huart3, sBuff, numChars);

State can be any 1, 5, 4, 6, 2 or 3.

Then in my Qt application I have 3 labels and want to show if corresponding bit is set in the number I receive from UART. I am sure I get the correct number, when I show it as integer its fine. But to break it down into 3 bits into three labels I fail as it just shows 1 1 1 or 0 0 0.

Here is my code on PC:

const void MotorWidget::setHallState(const QString& s)
{
 int hallState = s.toInt();
 ui->lbValueHallC->setText(hallState & 0b100 > 0 ? "1" : "0");
 ui->lbValueHallB->setText(hallState & 0b010 > 0 ? "1" : "0");
 ui->lbValueHallA->setText(hallState & 0b001 > 0 ? "1" : "0");
}

For example, if I receive hallState as 5, label C should show "1", label B should show "0" and label A should show "1"...but as I said I only get 111 or 000 regardless of what I receive.

I suspect this might be big-endian little-endian thing...but I have no idea how to fix it

As an aside: your API should be `setHallState(int)` or even `setHallState(HallState)`, where `HallState` is an enum or enum class. — Kuba hasn't forgotten Monica, May 31 '18 at 20:55
@KubaOber well for me it is easier to just receive ascii characters from the micro-controller...but I know what you mean...thanks/ — DEKKER, Jun 01 '18 at 10:22
ASCII characters aren't a `QString`!!! They are `QByteArray`. — Kuba hasn't forgotten Monica, Jun 01 '18 at 10:59

score 2 · Accepted Answer · answered May 30 '18 at 15:19

Maybe add some parentheses:

const void MotorWidget::setHallState(const QString& s)
{
 int hallState = s.toInt();
 ui->lbValueHallC->setText((hallState & 0b100) > 0 ? "1" : "0");
 ui->lbValueHallB->setText((hallState & 0b010) > 0 ? "1" : "0");
 ui->lbValueHallA->setText((hallState & 0b001) > 0 ? "1" : "0");
}

Also have a look here: http://en.cppreference.com/w/cpp/language/operator_precedence

Elvis Dukaj · Answer 2 · 2018-05-30T15:10:26.443

0

If you can I suggest you to use Boost C++ libraries: in this link you can find all you need.

If you're using GCC you can use the int32_t __builtin_bswap32 (int32_t x)

Alternative you can write you own function... it's quite easy, at this post

edited May 30 '18 at 15:10

answered May 30 '18 at 15:08

Elvis Dukaj

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I don't want to use a huge library just for something simple really – DEKKER May 30 '18 at 15:09

Convert and mask bits of little endian to big endian

2 Answers2