34. Count Set Bits in an 8-bit Register

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

uint8_t count_set_bits(uint8_t reg) {
    // Your code here
    reg = reg - ((reg >> 1) & 0x55);
    reg = (reg & 0x33) + ((reg >> 2) & 0x33);
    reg = (reg + (reg >> 4)) & 0x0F;
    return reg & 0xFF;
}

int main() {
    uint8_t reg;
    scanf("%hhu", &reg);
    printf("%u", count_set_bits(reg));
    return 0;
}