BCD转int

//template params：N number digits. S start position
//sample data  {0x12, 0x34, 0x56, 0x78, 0x9F}   if (N=4,S=1) then result = 2345
template <int N,int S=0>
class bcd_to_int
{
public:
	static int parse(char* src)
	{
		static_assert(sizeof(int)==4, "int must be 4 byte");
		static_assert(N <= 10,"int not exceed 10 digits");
		static_assert(S==1 || S==0, "S int [0,1]");

		char buff[N + 1] = { 0 };

		typedef std::conditional<S%2 == 0, std::true_type, std::false_type>::type is_even_type;

		parse_helper<N>(src, buff, is_even_type());
		
		return boost::lexical_cast<int>(buff); ;
	}
	
	template<int N>
	static void parse_helper(char* src, char* buff, std::true_type)
	{	
		buff[0] = ((*src & 0xF0) >> 4) + 0x30;
		parse_helper<N-1>(src, buff + 1, std::false_type());
	}

	template<>
	static void parse_helper<0>(char* src, char* buff, std::true_type)
	{}

	template<int N>
	static void parse_helper(char* src, char* buff,std::false_type)
	{
		buff[0] = (*src & 0x0F) + 0x30;
		parse_helper<N-1>(src + 1, buff + 1, std::true_type());
	}

	template<>
	static void parse_helper<0>(char* src, char* buff,std::false_type)
	{}
};


int main()
{
	char src[] = { 0x89,0x89,0x89,0x89,0x89 };

	int ret = bcd_to_int<9>::parse(src);  //999999999

	//bcd_to_int<10>::parse(src);  will throw error

	ret = bcd_to_int<3,1>::parse(src);   //989

	return 0;
}