22. Extract Even Bits Only from 32-bit Register

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

#define set(reg,pos) (reg |= (1 << (pos)))

uint32_t extract_even_bits(uint32_t reg) {
    // Your code here
    // uint32_t result = 0;
    // for(int i = 0 ; i < 32 ; i += 2){
    //     if(reg & ( 1 << i)){
    //         set(result,i/2);
    //     }
    // }
    // return result;
    reg = reg & 0x55555555;
    reg = (reg | reg >> 1) & 0x33333333;
    reg = (reg | reg >> 2) & 0x0f0f0f0f;
    reg = (reg | reg >> 4) & 0x00ff00ff;
    reg = (reg | reg >> 8) & 0x0000ffff;
    return reg;
}

int main() {
    uint32_t reg;
    scanf("%u", &reg);
    printf("%u", extract_even_bits(reg));
    return 0;
}