Ad 1. Those types are designed to work with numbers with huge dynamic range. The long double is implemented in a native way in the x87 FPU. The 128b double I suspect would be implemented in software mode on modern x86s, as there’s no hardware to do the computations in hardware. The funny thing is … Read more
You can find out with std::numeric_limits: #include <iostream> // std::cout #include <limits> // std::numeric_limits int main(){ std::cout << std::numeric_limits<long double>::digits10 << std::endl; }
I’m not sure why you think that long double was “abandoned”, as it is part of the C++ Standard and therefore a compliant implementation must, well, implement it. What they did “abandon” is long double overloads of mathematical functions, and they did this because: In Win32 programming, however, the long double data type maps to … Read more
There’s a similar problem with MinGW under Windows. If that’s not what you’re using, this answer probably doesn’t apply. The problem is that the compiler (GCC) and the runtime library (Microsoft’s) are implemented by different groups that happen to have different ideas about how the type long double should be represented. (gcc uses 128 bits … Read more
Quoting from Wikipedia: On the x86 architecture, most compilers implement long double as the 80-bit extended precision type supported by that hardware (sometimes stored as 12 or 16 bytes to maintain data structure . and Compilers may also use long double for a 128-bit quadruple precision format, which is currently implemented in software. In other … Read more
Yes — for long double, you need to use %Lf (i.e., upper-case ‘L’).