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

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

#define SET_MODE(reg, mode) ((reg) |= ((((1 << 3)-1) & (mode))));
#define SET_SPEED(reg, speed) ((reg) |= (((((1 << 5)-1)) & (speed)) << 3));
#define SET_STATUS(reg, status) ((reg) |= ((((1 << 6)-1) & (status)) << 10));

uint16_t pack_register(uint8_t mode, uint8_t speed, uint8_t status) {

    uint16_t reg = 0;
    SET_MODE(reg, mode);
    SET_SPEED(reg, speed);
    SET_STATUS(reg, 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;
}