- dnl function. With gcc >= 4.3 on glibc/x86_64, calls to the 'fabs' function
- dnl are inlined by the compiler, therefore linking of these calls does not
- dnl require -lm, but taking the function pointer of 'fabs' does.
+ dnl function.
+ dnl 1) With gcc >= 4.3 on glibc/x86_64, calls to the 'fabs' function
+ dnl are inlined by the compiler, therefore linking of these calls does
+ dnl not require -lm, but taking the function pointer of 'fabs' does.
+ dnl 2) On MSVC 9, many math functions exist only as macros with arguments,
+ dnl whereas the function pointer is undefined.
+ dnl On the other hand, taking just the function pointer is not enough.
+ dnl 1) On AIX 7.1, when 'long double' is 128 bit large ("xlc -qldbl128" or
+ dnl "xlc -qlongdouble" or "gcc -mlong-double-128") many math functions
+ dnl exist as macros with arguments, that may reference libm or even
+ dnl completely undefined functions such as __rint128.
+ dnl 2) In AIX 7.1 with gcc 4.2, when optimization is turned on, calls to
+ dnl rint() with simple arguments are turned into rintf() calls by the
+ dnl compiler. But while rint() is resides in libc, rintf() is in libm.