Macro-Based Register Config Helper

Code

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

// Define macros here
/*
    1. get the width_mask: ((1U << lsb) - 1)
    2. get the position mask: (width_mask << lsb)
    3. clear the destination bits: x & ~position_mask
    4. sanitize and shift the value: (v & width_mask) << lsb
    5. or them together: (x & ~position_mask) | ((v & width_mask) << lsb)

    (x & ~position_mask) | ((v & width_mask) << lsb)
    (x & ~(width_mask << lsb)) | ((v & width_mask) << lsb)
    (x & ~(((1U << lsb) - 1) << lsb)) | ((v & ((1U << lsb) - 1)) << lsb)

    Add extra parentheses
    ((x) & ~(((1U << lsb) - 1) << lsb)) | (((v) & ((1U << lsb) - 1)) << lsb))

*/

#define SET_ENABLE(reg, v) ((reg) = (((reg) & ~(1U)) | ((v) & 1U)))
#define SET_MODE(reg, v) ((reg) = (((reg) & ~(((1U << 2U) - 1U) << 1U)) | ((((v) & ((1U << 2U) - 1U)) << 1U))))
#define SET_SPEED(reg, v) ((reg) = (((reg) & ~(((1U << 3U) - 1U) << 3U)) | ((((v) & ((1U << 3U) - 1U)) << 3U))))

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

    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