Additional Floating Types#
ISO/IEC TS 18661-3:2015 defines C support for additional floating
types _Floatn
and _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 fn
or
Fn
and fnx
or Fnx
. These type
names can be used together with _Complex
to declare complex
types.
As an extension, GNU C and GNU C++ support additional floating types, which are not supported by all targets.
__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 forlong double
.__float80
is 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_Float64x
on these targets.__ibm128
is available on PowerPC targets, and provides access to the IBM extended double format which is the current format used forlong double
. Whenlong double
transitions to__float128
on PowerPC in the future,__ibm128
will 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 __float128
.
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.
The _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
systems where __float128
is supported. The _Float32
type is supported on all systems supporting IEEE binary32; the
_Float64
and _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
support _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, XCmode
for
__float80
type and TCmode
for __float128
type:
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, 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;