22. Extract Even Bits Only from 32-bit Register

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

uint32_t extract_even_bits(uint32_t reg) {
    reg &= 0x55555555U;

    reg = (reg | (reg >> 1)) & 0x33333333U;
    reg = (reg | (reg >> 2)) &  0x0F0F0F0FU;
    reg = (reg | (reg >> 4)) & 0x00FF00FFU;
    reg = (reg | (reg >> 8)) & 0x0000FFFFU;

    return reg;
}

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