76. Construct UART Data Frame with Parity Bit

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

// UART Control Register Struct: 8-bit total
typedef struct {
    uint8_t parity_enable : 1;   // 0 = disabled, 1 = enabled
    uint8_t parity_type   : 1;   // 0 = even, 1 = odd
    uint8_t reserved      : 6;   // unused
} UART_Control;

int cnt(uint8_t data) {
    int c = 0;
    while (data > 0) {
        data &= (data - 1);
        c++;
    }
    return c;
}

uint8_t create_uart_frame(uint8_t data, UART_Control *ctrl) {
    data &= 0x7F;
    int p = (cnt(data) % 2 == 0) ? 0 : 1;

    if (ctrl -> parity_enable == 0) {
        return data;
    }

    p ^= ctrl -> parity_type;
    return (p << 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;
}