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

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

union Register{
    struct{
        uint16_t mode:3;
        uint16_t speed:5;
        uint16_t reserved:2;
        uint16_t status:6;
    }bits;
    uint16_t final_val;
};

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

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;
}