25. Pack Multiple Fields into a 16-bit Control Register

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

typedef union {
    uint16_t field;
    struct {
        uint16_t Mode     : 3;
        uint16_t Speed    : 5;
        uint16_t Reserved : 2;
        uint16_t Status   : 6;
    };
} ctrl;


uint16_t pack_register(uint8_t mode, uint8_t speed, uint8_t status) {
    ctrl word;
     word.Mode = mode;
     word.Speed = speed;  
     word.Status = status;

    return word.field;
}

int main() {
    uint8_t mode, speed, status;
    scanf("%hhu %hhu %hhu", &mode, &speed, &status);

    uint16_t reg = pack_register(mode, speed, status);
    printf("%u", reg);
    return 0;
}