What are the requirements to use __float128?

Question

I'm not really sure how I can find out of a system does or doesn't support the __float128 type. What system requirements have to be met for this to be available, and is there a way to check if those requirements are met in C code? (For reference, my system supports __int128 but not __float128 .)

Answer 1

Suppose you are asking about GCC, clause 6.12 of the documentation for GCC 10.2 says:

… __float128 is available on i386, x86_64, IA-64, and hppa HP-UX, as well as on PowerPC GNU/Linux targets that enable the vector scalar (VSX) instruction set. __float128 supports the 128-bit floating type. On i386, x86_64, PowerPC, and IA-64 other than HP-UX, __float128 is an alias for _Float128 . On hppa and IA-64 HP-UX, __float128 is an alias for long double …

and:

… In order to use _Float128 , __float128 , and __ibm128 on PowerPC Linux systems, you must use the -mfloat128 option. It is expected in future versions of GCC that _Float128 and __float128 will be enabled automatically…

I do not see an in-source test for the type, such as a preprocessor macro that would indicate it.