22. Extract Even Bits Only from 32-bit Register

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

uint32_t extract_even_bits(uint32_t reg) {
    if (reg == 0) return 0;
    reg = reg & 0x55555555;
    reg = ((reg>>1) & 0x22222222) | (reg & 0x11111111);
    reg = ((reg>>2) & 0x0C0C0C0C) | (reg & 0x03030303);
    reg = ((reg>>4) & 0x00F000F0) | (reg & 0x000F000F);
    reg = ((reg>>8) & 0x0000FF00) | (reg & 0x000000FF);
    return reg;
}

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