flipcode - Bits Needed To Store A Value At Compile-time

/// Implementation use by the Macro VALUE_TO_NB_BITS(x)
template<unsigned N struct NbBits
{
        enum
        {
                Val =  1 + NbBits< (N  1) ::Val 
        };
};

/// End of recursive calls
template< struct NbBits<0
{
        enum

        {
                Val =  0 
        };
};

/// Macro which compute number of bits to store value 'x'
#define VALUE_TO_NB_BITS(x)  ( NbBits<(x)::Val )

/// Sample
enum 
{
        VALUE0,
        VALUE1,
        VALUE2,
        VALUE3,
        VALUE4,
        VALUE5,
        NB_VALUES
};

#include <stdio.h 
#include <stdlib.h 


/// Main
int main()
{
    printf("%d-%d bits, %d-%d bits, %d-%d bits %d-%d bits\n",
              3, VALUE_TO_NB_BITS(3),
              4, VALUE_TO_NB_BITS(4),
              50, VALUE_TO_NB_BITS(50),
              NB_VALUES-1, VALUE_TO_NB_BITS(NB_VALUES-1)
           );
   
   // Output : 
   // 3-2 bits, 4-3 bits, 50-6 bits 5-3 bits

   return 0;
}