76. Construct UART Data Frame with Parity Bit

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

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

int count_1s_in_7bit_data(uint8_t input){
    int count = 0;
    for(int i = 0; i <7; i++)
    {
        if( ((input >>i) &1) == 1)
        {
            count++;
        }
    }
    return count;
}

uint8_t create_uart_frame(uint8_t data, UART_Control *ctrl) {
    
    // parity disable
    if(ctrl->parity_enable == 0)
    {
        data &= ~(1 << 7); // parity-enable bit -> 0
    }
    else
    {
        // check total number of 1s (including parity) 
        if(ctrl->parity_type == 0) // even
        {
            if(count_1s_in_7bit_data(data) %2 == 0)
            {
                data &= ~(1 << 7); // parity-enable bit -> 0
            }
            else
            {
                data |= (1 << 7); // parity-enable bit -> 1
            } 

        }
        else{ // odd parity
            if(count_1s_in_7bit_data(data) %2 == 0)
            {
                data |= (1 << 7); // parity-enable bit -> 1
            }
            else
            {
                data &= ~(1 << 7); // parity-enable bit -> 0
            } 
        }
    }
    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;
}