Count the number of set bits in a byte/int32

int pop(unsigned x)
{
    x = x - ((x >> 1) & 0x55555555);
    x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
    x = (x + (x >> 4)) & 0x0F0F0F0F;
    x = x + (x >> 8);
    x = x + (x >> 16);
    return x & 0x0000003F;
}

=======================================================

long count_bits(long n) {     
  unsigned int c; // c accumulates the total bits set in v
  for (c = 0; n; c++) 
    n &= n - 1; // clear the least significant bit set
  return c;
}=======================================================
unsigned int bitCount (unsigned int value) {
    unsigned int count = 0;
    while (value > 0) {           // until all bits are zero
        if ((value & 1) == 1) {   // check lower bit
            count++;
        }
        value /= 2;               // shift bits, removing lower bit
    }
    return count;
}