ISO/IEC TS 18661-3:2015 defines C support for additional floating
_Floatnx, and GCC supports
these type names; the set of types supported depends on the target
architecture. These types are not supported when compiling C++.
Constants with these types use suffixes
Fnx. These type
names can be used together with
_Complex to declare complex
As an extension, GNU C and GNU C++ support additional floating types, which are not supported by all targets.
__float128is 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.
__float128supports the 128-bit floating type. On i386, x86_64, PowerPC, and IA-64 other than HP-UX,
__float128is an alias for
_Float128. On hppa and IA-64 HP-UX,
__float128is an alias for
__float80is available on the i386, x86_64, and IA-64 targets, and supports the 80-bit (
XFmode) floating type. It is an alias for the type name
_Float64xon these targets.
__ibm128is available on PowerPC targets, and provides access to the IBM extended double format which is the current format used for
long double. When
long doubletransitions to
__float128on PowerPC in the future,
__ibm128will remain for use in conversions between the two types.
Support for these 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
In order to use
on PowerPC Linux systems, you must use the -mfloat128 option. It is
expected in future versions of GCC that
will be enabled automatically.
_Float128 type is supported on all systems where
__float128 is supported or where
long double has the
IEEE binary128 format. The
_Float64x type is supported on all
__float128 is supported. The
type is supported on all systems supporting IEEE binary32; the
_Float32x types are supported on all systems
supporting IEEE binary64. The
_Float16 type is supported on AArch64
systems by default, on ARM systems when the IEEE format for 16-bit
floating-point types is selected with -mfp16-format=ieee and,
for both C and C++, on x86 systems with SSE2 enabled. GCC does not currently
_Float128x on any systems.
On the i386, x86_64, IA-64, and HP-UX targets, you can declare complex
types using the corresponding internal complex type,
__float80 type and
typedef _Complex float __attribute__((mode(TC))) _Complex128; typedef _Complex float __attribute__((mode(XC))) _Complex80;
On the PowerPC Linux VSX targets, you can declare complex types using
the corresponding internal complex type,
__float128 type and
typedef _Complex float __attribute__((mode(KC))) _Complex_float128; typedef _Complex float __attribute__((mode(IC))) _Complex_ibm128;