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

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

#define MODE_MASK       ((1u << 3) - 1) //BIT 0-2  
#define SPEED_MASK      ((1u << 7) -1)//BIT 3-7
#define STATUS_MASK     ((1u << 6) -1) // BIT 10-15

#define SPEED_POS       3
#define STATUS_POS      10


uint16_t pack_register(uint8_t mode, uint8_t speed, uint8_t status) {
    return( (mode & MODE_MASK) | ((speed & SPEED_MASK) << SPEED_POS) | 
            ((status & STATUS_MASK) << STATUS_POS) );
}

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;
}