Pack Multiple Fields into a 16-bit Control Register

Code

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

#define ONES_MASK(pos, len) ((1u << (len)) - 1) << pos
#define CLEARED_MASK(pos, len) (~(ONES_MASK(pos, len)))

#define SET_FIELD(reg, pos, len, val) \
    ((reg) = (((reg) & CLEARED_MASK(pos, len)) | ( (((val) & ((1u << (len)) - 1u)) << (pos)) )))

uint16_t pack_register(uint8_t mode, uint8_t speed, uint8_t status) {
    // Your logic here

    uint16_t reg = 0;
    
    // Set Mode:
    SET_FIELD(reg, 0, 3, mode);
    
    // Set Speed:
    SET_FIELD(reg, 3, 5, speed);

    // Ensure Reserved field is cleared always: 
    SET_FIELD(reg, 8, 2, 0);

    // Set Status:
    SET_FIELD(reg, 10, 6, status);

    return 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;
}

Solving Approach