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

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

typedef union {
    struct {
        uint16_t mode : 3;
        uint16_t speed : 5;
        uint16_t reserved : 2;
        uint16_t status : 6;
    } fields;
    uint16_t reg;
} Register;

uint16_t pack_register(uint8_t mode, uint8_t speed, uint8_t status) {
    
    Register r;
    r.fields.mode = mode;
    r.fields.speed = speed;
    r.fields.reserved = 0;
    r.fields.status = status;

    return r.reg;
}

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;
}