Construct UART Data Frame with Parity Bit

Code

#include <stdio.h>
#include <stdint.h>

typedef struct {
    uint8_t parity_enable : 1;   // 0 = Disabled, 1 = Enabled
    uint8_t parity_type   : 1;   // 0 = Even parity, 1 = Odd parity
    uint8_t reserved      : 6;
} UART_Control;


typedef struct {
    uint8_t data   : 7;  // lower 7 bits
    uint8_t parity : 1;  // MSB
} FrameData_t;

uint8_t create_uart_frame(uint8_t data, UART_Control *ctrl) {
    FrameData_t frame;

    // mask to 7 bits
    frame.data = data & 0x7F;

    if (ctrl->parity_enable == 0) {
        frame.parity = 0;  // no parity, MSB=0
    } else {
        int ones = 0;
        uint8_t temp = frame.data;
        while (temp) {
            ones += temp & 1;
            temp >>= 1;
        }

        if (ctrl->parity_type == 0) {      // Even parity
            frame.parity = (ones % 2 != 0);
        } else {                           // Odd parity
            frame.parity = (ones % 2 == 0);
        }
    }

    return *((uint8_t *)&frame);  // pack into byte
}

int main() {
    uint8_t data;
    scanf("%hhu", &data);  // 7-bit input

    uint8_t parity_enable, parity_type;
    scanf("%hhu %hhu", &parity_enable, &parity_type);

    UART_Control ctrl;
    ctrl.parity_enable = parity_enable;
    ctrl.parity_type   = parity_type;

    uint8_t frame = create_uart_frame(data, &ctrl);
    printf("frame = 0x%02X\n", frame);

    return 0;
}

Solving Approach