Construct UART Data Frame with Parity Bit

Code

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

#define MASK(width, pos) (((1u<<width)-1)<<pos)

typedef struct {
    uint8_t parity_enable : 1;
    uint8_t parity_type   : 1;
    uint8_t reserved      : 6;
} UART_Control;

uint8_t count_set_bits(uint8_t data){
    uint8_t size = sizeof(data) * 8 - 1; // exclude MSB
    uint8_t set_bits = 0;
    for (int i=0; i<size; i++){
        if (data & (1u<<i)){
            set_bits++;
        }
    }

    return set_bits;
}

uint8_t create_uart_frame(uint8_t data, UART_Control *ctrl) {
    uint8_t uart_frame = 0;
    if (ctrl->parity_enable == 0){
        // MSB:0, data is 7 other bits
        uart_frame |= (data & MASK(7,0));
        return uart_frame;
    }
    
    uint8_t set_bits = count_set_bits(data);
    if ((ctrl->parity_type == 0) && (set_bits % 2 != 0)){ //even parity
            uart_frame |= (1u<<7); // 1s are odd
        }

    else if ((ctrl->parity_type != 0) && (set_bits % 2 == 0)){ // odd parity
          uart_frame |= (1u<<7); // 1s are even
    }

    uart_frame |= (data & MASK(7,0));
    return uart_frame;
}

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", frame);

    return 0;
}

Solving Approach