Template meta-program for bit counting of constants

popcount.h

#include <stdint.h>

template< uint32_t x >
struct PopCount
{
  static const uint32_t n = PopCount< x / 2 >::n + ( x % 2 );
};

template<>
struct PopCount< 0 >
{
  static const uint32_t n = 0;
};

const static uint32_t a = PopCount<2>::n;
const static uint32_t b = PopCount<4>::n;
const static uint32_t c = PopCount<3>::n;
const static uint32_t d = PopCount<5>::n;

static_assert( a == b, "bit count mismatch in compile constant" );
static_assert( c == d, "bit count mismatch in compile constant" );
static_assert( a != c, "bit count mismatch in compile constant" );
static_assert( b != d, "bit count mismatch in compile constant" );