If you compile modules that perform floating-point operations and plan to include these modules in a libraryThe calls to emulator option (/FPc) generates floating-point calls to the emulator library and places the names of an emulator library (mLIBCE.LIB) in the object file. At link time, you can specify a math coprocessor library (mLIBC7.LIB) or an alternate math library (mLIBCA.LIB) instead. Thus, /FPc gives you more flexibility in the libraries you can use for linking than the inline emulator option.
Using the calls to emulator option is also recommended in the following cases:
If you compile modules that perform floating-point operations and plan to include these modules in a library
If you compile modules that you want to link with libraries other than the libraries provided with Microsoft C/C++
You cannot link with an alternate math library if your program uses the intrinsic forms of floating-point library routines (that is, if you have compiled the program with the /Oi or /Ox option, selected the Generate Intrinsic Functions option from the Optimizations dialog box in the Programmer's WorkBench, or specified math functions in an intrinsic pragma).