Macro-Based Register Config Helper

Code

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

// Define macros here
#define set_enable(enable) ((enable&0x1)<<0);
#define set_mode(mode) ((mode&0x3)<<1);
#define set_speed(speed) ((speed&0x7)<<3);

uint16_t build_register(uint8_t enable, uint8_t mode, uint8_t speed) {
    // Use macros to set fields
    uint16_t reg = 0;
    reg |= set_enable(enable);
    reg |= set_mode(mode);
    reg |= set_speed(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

How each macro works:

#define set_enable(enable) ((enable&0x1)<<0);  enable can be either 1 or 0, so we take the value to be 1 and use and operator to find the value and left shift 0 times as its the first bit to be set.

#define set_mode(mode) ((mode&0x3)<<1); mode can either be 1 or 2. so that is either 01 or 10. So we use a bit mask of 3(11) and then find the required mode and shift by 1 to set the correct bits.

#define set_speed(speed) ((speed&0x7)<<3); speed can be any value from 0 to 7 so we make that bit mask to be 7(111). Then find the required speed and left shift by 3 bits to set the correct bits.