Macro-Based Register Config Helper

Code

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

// position macro
#define ENABLE_POS  0U
#define MODE_POS    1u
#define SPEED_POS   3u

#define ENABLE_MASK (1u << ENABLE_POS)
#define MODE_MASK   (0x3u << MODE_POS)
#define SPEED_MASK  (0X7u << SPEED_POS)
#define RESERVED_MASK (0x3u << 6)

/* Marcos: clear the field first (so we don't disturb other bits),
   then OR in the masked/shifted value. */

#define SET_ENABLE(reg, en) \
    do { (reg) = (uint16_t)((reg & ~ENABLE_MASK) | (((uint16_t)((en) & 0x1u)) << ENABLE_POS)); } while(0)

#define SET_MODE(reg, mode) \
    do { (reg) = (uint16_t)((reg & ~MODE_MASK) | (((uint16_t)((mode) & 0x3u)) << MODE_POS)); } while(0)

#define SET_SPEED(reg, speed) \
    do { (reg) = (uint16_t)((reg & ~SPEED_MASK) | (((uint16_t)((speed) & 0x7u)) << SPEED_POS)); } while(0)

// used for debuging
void print_binary(uint16_t n) {
    int bits = sizeof(n) * 8;   // number of bits in the type
    for (int i = bits - 1; i >= 0; i--) {
        putchar((n & (1u << i)) ? '1' : '0');
    }
    putchar('\n');
}

uint16_t build_register(uint8_t enable, uint8_t mode, uint8_t speed) {
    // Use macros to set fields
    uint16_t reg = 0;
    SET_MODE(reg, mode);
    SET_ENABLE(reg, enable);
    SET_SPEED(reg, speed);

    // Optionally enforce: zero out RESERVED defensively (should already be 0)
    reg &= (uint16_t)~RESERVED_MASK;
    return reg;
}

int main() {
    uint8_t enable, mode, speed;
    scanf("%hhu %hhu %hhu", &enable, &mode, &speed);

    uint16_t reg = build_register(enable, mode, speed);
    printf("%u", reg);
    return 0;
}

Solving Approach