Pack Multiple Fields into a 16-bit Control Register

Code

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

typedef struct {
    union {
        uint16_t value;
        struct {   
            unsigned mode  : 3;
            unsigned speed : 5;
            unsigned reserved : 2;
            unsigned status : 6;
        } bits_struct;
    };
} Register;

uint16_t pack_register(uint8_t mode, uint8_t speed, uint8_t status) {
    Register reg;
    reg.bits_struct.mode = mode;
    reg.bits_struct.speed = speed;
    reg.bits_struct.reserved = 0;
    reg.bits_struct.status = status;
    return reg.value;
}

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;
}