C inline directive

inline.c

/*
Forcing inlining is useful if:
- inline is not respected by the compiler (ignored by compiler cost/benefit analyzer), and
- inlining results in a necessary performance boost

For code portability, the following preprocessor directives may be used:
*/

#ifdef _MSC_VER
    #define forceinline __forceinline
#elif defined(__GNUC__)
    #define forceinline inline __attribute__((__always_inline__))
#elif defined(__CLANG__)
    #if __has_attribute(__always_inline__)
        #define forceinline inline __attribute__((__always_inline__))
    #else
        #define forceinline inline
    #endif
#else
    #define forceinline inline
#endif

/*!
\warning gcc cannot inline functions if[3]
- they are variadic,
- use \c alloca
- use computed \c goto
- use nonlocal \c goto
- use nested functions
- use \c setjmp
- use \c __builtin_longjmp
- use \c __ builtin_return, or
- use \c __builtin_apply_args
*/