Construct UART Data Frame with Parity Bit

Code

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

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

uint8_t create_uart_frame(uint8_t data, UART_Control *ctrl) {
    
    if (ctrl -> parity_enable == 1) {
        // Count ones
        uint8_t num_ones = 0;
        for (uint8_t i = 0; i < 8; i++) {
            num_ones += ((data >> i) & 1);
        }
        
        // Clear 8th bit
        data &= ~(1 << 7);
        // Trick: truth table for the parity_type and num_ones equals to an xor
        data |= (ctrl -> parity_type ^ num_ones) << 7;
    } 
    
    return data;
}

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