Pack Multiple Fields into a 16-bit Control Register

#include <stdio.h>
#include <stdint.h>
#define MODE_POS 0
#define MODE_LEN 3

#define SPEED_POS 3
#define SPEED_LEN 5

#define RESERVED_POS 8
#define RESERVED_LEN 2

#define STATUS_POS 10
#define STATUS_LEN 6

#define FIELD_PREP(val, len, pos) \
   (((uint16_t)((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;
    
    reg |= FIELD_PREP(mode,   MODE_LEN,   MODE_POS);    // bits 0..2
    reg |= FIELD_PREP(speed,  SPEED_LEN,  SPEED_POS);   // bits 3..7
    reg |= FIELD_PREP(status, STATUS_LEN, STATUS_POS);  // bits 10..15
    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;
}