Get the compilation time in unix time

cx_compile_time_unix.hpp

namespace cx
{
	constexpr bool cx_strcmp_part(const char* const a, const char* const b)
	{
		return *b ? (*a == *b && cx_strcmp_part(a + 1, b + 1)) : true;
	}

	constexpr unsigned month_str_to_int(const char* const str)
	{
		return
			cx_strcmp_part(str, "Jan") ? 1 :
			cx_strcmp_part(str, "Feb") ? 2 :
			cx_strcmp_part(str, "Mar") ? 3 :
			cx_strcmp_part(str, "Apr") ? 4 :
			cx_strcmp_part(str, "May") ? 5 :
			cx_strcmp_part(str, "Jun") ? 6 :
			cx_strcmp_part(str, "Jul") ? 7 :
			cx_strcmp_part(str, "Aug") ? 8 :
			cx_strcmp_part(str, "Sep") ? 9 :
			cx_strcmp_part(str, "Oct") ? 10 :
			cx_strcmp_part(str, "Nov") ? 11 : 12;
	}

	constexpr unsigned char_to_int(const unsigned char c)
	{
		return (c == ' ' ? '0' : c) - '0';
	}

	constexpr unsigned twochar_to_int(const char* const str)
	{
		return (char_to_int(str[0])) * 10 + char_to_int(str[1]);
	}

	constexpr unsigned year_str_to_int(const char* const str)
	{
		return (char_to_int(str[0])) * 1000 + (char_to_int(str[1])) * 100 + (char_to_int(str[2])) * 10 + char_to_int(str[3]);
	}

	constexpr unsigned days_from_civil(int y, int m, int d)
	{
		const int yc = y - (m <= 2 ? 1 : 0);
		const int era = (yc >= 0 ? yc : yc - 399) / 400;
		const unsigned yoe = static_cast<unsigned>(yc - era * 400);				// [0, 399]
		const unsigned doy = (153 * (m + (m > 2 ? -3 : 9)) + 2) / 5 + d - 1;	// [0, 365]
		const unsigned doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;				// [0, 146096]
		return era * 146097 + int(doe) - 719468;
	}

	constexpr unsigned date_str_to_days(const char* const str)
	{
		return days_from_civil(year_str_to_int(str + 7), month_str_to_int(str), twochar_to_int(str + 4));
	}

	constexpr unsigned time_str_to_second(const char* const str)
	{
		return (twochar_to_int(str) * 60 + twochar_to_int(str + 3)) * 60 + twochar_to_int(str + 6);
	}

	constexpr uint64_t unix_time()
	{
		return uint64_t(date_str_to_days(__DATE__)) * 24 * 60 * 60 + time_str_to_second(__TIME__);
	}
}