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_ones(uint8_t data){
    int count;
    for(int i=0;i<7;i++){
        if(data & (1<<i)){
            count++;
        }
    }
    return count;
}

uint8_t create_uart_frame(uint8_t data, UART_Control *ctrl) {
    //1. Ensure data only has 7 bits (0111 1111)
    data = data & 0x7F;    
    
    //2. Check for parity disabled
    if(ctrl->parity_enable == 0){
        //Ensure MSB of data is a 0 (clear MSB) & return
        data &= ~(1 << 7);
        return data; 
    }

    //3. Check for parity enabled
    //Count the number of 1st in the 7bit data
    int count = count_ones(data); 
    int parity_bit;   
    
    //If EVEN parity bit setting
    if(ctrl->parity_type == 0){
        //If ones are even, set parity to 0 else set parity to 1
        parity_bit = (count % 2 == 0) ? 0:1;
        }
    //If ODD parity bit setting
    else { 
        //If ones are even, set parity to 1 else set parity to 0
        parity_bit = (count % 2 == 0) ? 1:0;
        }

    //4. Return data with correct parity bit
    return data |= (parity_bit << 7);
}

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;
}