22. Extract Even Bits Only from 32-bit Register

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

uint32_t extract_even_bits(uint32_t reg) 
{
    // Your code here
    unsigned short i;
    uint32_t mask, unit, extractor;
    uint16_t ans;
    mask = unit = 0b1;
    for (i = 0; i < 16; ++i)
    {
        mask = (mask << 2) | unit;
    }
    extractor = reg & mask;
    for (i = 0; i <= 15; ++i)
    {
        if ((extractor >> 2*i) & 1) ans |= 1 << i;
    }
    return ans;
}

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