As an extension, GNU C supports additional floating
types, __float80 and __float128 to support 80-bit
(XFmode) and 128-bit (TFmode) floating types.
Support for additional types includes the arithmetic operators:
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types. Use a suffix ‘w’ or ‘W’
in a literal constant of type __float80 or type
__ibm128. Use a suffix ‘q’ or ‘Q’ for _float128.
On the i386, x86_64, IA-64, and HP-UX targets, you can declare complex
types using the corresponding internal complex type, XCmode for
__float80 type and TCmode for __float128 type:
typedef _Complex float __attribute__((mode(TC))) _Complex128; typedef _Complex float __attribute__((mode(XC))) _Complex80;
In order to use __float128 and __ibm128 on PowerPC Linux
systems, you must use the -mfloat128. It is expected in
future versions of GCC that __float128 will be enabled
automatically. In addition, there are currently problems in using the
complex __float128 type. When these problems are fixed, you
would use the following syntax to declare _Complex128 to be a
complex __float128 type:
On the PowerPC Linux VSX targets, you can declare complex types using
the corresponding internal complex type, KCmode for
__float128 type and ICmode for __ibm128 type:
typedef _Complex float __attribute__((mode(KC))) _Complex_float128; typedef _Complex float __attribute__((mode(IC))) _Complex_ibm128;
Not all targets support additional floating-point types.
__float80 and __float128 types are supported on x86 and
IA-64 targets. The __float128 type is supported on hppa HP-UX.
The __float128 type is supported on PowerPC 64-bit Linux
systems by default if the vector scalar instruction set (VSX) is
enabled.
On the PowerPC, __ibm128 provides access to the IBM extended
double format, and it is intended to be used by the library functions
that handle conversions if/when long double is changed to be IEEE
128-bit floating point.