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;

uint8_t create_uart_frame(uint8_t data, UART_Control *ctrl) {
    uint8_t parity = 0U;

    // ensure data does not overflow
    data = data & 0x7F;

    // configure bit 7
    if (ctrl->parity_enable) {
        // count number of 1's in the data
        int cnt = 0;
        for (int i = 0; i < 7; i++) {
            cnt += (data >> i) & 1U;
        }

        // set parity bit
        if (cnt % 2 == 0) {
            // even number of 1's
            parity = ctrl->parity_type; 
        } else {
            // odd number of 1's
            parity = !ctrl->parity_type;
        }
    }

    return (parity << 7) | 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;
}