#include <bit>
#include <cstdint>




static const unsigned char BitsSetTable256[256] =
{
#   define B2(n) n,     n+1,     n+1,     n+2
#   define B4(n) B2(n), B2(n+1), B2(n+1), B2(n+2)
#   define B6(n) B4(n), B4(n+1), B4(n+1), B4(n+2)
    B6(0), B6(1), B6(1), B6(2)
};

uint32_t main(uint32_t v)
{
  unsigned int c; // c is the total bits set in v

  // Option 1:
  c = BitsSetTable256[v & 0xff] +
    BitsSetTable256[(v >> 8) & 0xff] +
    BitsSetTable256[(v >> 16) & 0xff] +
    BitsSetTable256[v >> 24];

 return c;
}