I'm going to use big numbers in C++ code on an embedded system. Luckily the compiler recognizes long doubles.
I can not use standard libraries, boost libraries, gnu math libraries, etc. And the system has not got built-in float math cpu.
Now how can I detect long double overflows?
As it's not standard C++, you will have to rely on methods provided by your specific environment. The manufacturer of the embedded system should have documented how it can be done. Ask him.