22. Extract Even Bits Only from 32-bit Register

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

#define GET_BIT32(r, n) (((r) >> (n)) & UINT32_C(1))

uint32_t extract_even_bits(uint32_t reg) {
    uint32_t res = reg & UINT32_C(0x55555555);

    res = ( res | (res >> 1) ) & UINT32_C(0x33333333);
    res = ( res | (res >> 2) ) & UINT32_C(0x0f0f0f0f);
    res = ( res | (res >> 4) ) & UINT32_C(0x00ff00ff);
    res = ( res | (res >> 8) ) & UINT32_C(0x0000ffff);

    return (uint16_t)res;
}

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