* Complex:: Data types for complex numbers.
* Floating Types:: Additional Floating Types.
* Half-Precision:: Half-Precision Floating Point.
-* Decimal Float:: Decimal Floating Types.
+* Decimal Float:: Decimal Floating Types.
* Hex Floats:: Hexadecimal floating-point constants.
* Fixed-Point:: Fixed-Point Types.
* Named Address Spaces::Named address spaces.
safe.
GCC implements taking the address of a nested function using a technique
-called @dfn{trampolines}. This technique was described in
+called @dfn{trampolines}. This technique was described in
@cite{Lexical Closures for C++} (Thomas M. Breuel, USENIX
C++ Conference Proceedings, October 17-21, 1988).
@}
return open (path, oflag, __builtin_va_arg_pack ());
@}
-
+
if (__builtin_va_arg_pack_len () < 1)
return __open_2 (path, oflag);
@cindex @code{__fp16} data type
On ARM targets, GCC supports half-precision (16-bit) floating point via
-the @code{__fp16} type. You must enable this type explicitly
+the @code{__fp16} type. You must enable this type explicitly
with the @option{-mfp16-format} command-line option in order to use it.
ARM supports two incompatible representations for half-precision
The @code{__fp16} type is a storage format only. For purposes
of arithmetic and other operations, @code{__fp16} values in C or C++
expressions are automatically promoted to @code{float}. In addition,
-you cannot declare a function with a return value or parameters
+you cannot declare a function with a return value or parameters
of type @code{__fp16}.
Note that conversions from @code{double} to @code{__fp16}
of rounding, this can sometimes produce a different result than a
direct conversion.
-ARM provides hardware support for conversions between
+ARM provides hardware support for conversions between
@code{__fp16} and @code{float} values
as an extension to VFP and NEON (Advanced SIMD). GCC generates
code using these hardware instructions if you compile with
-options to select an FPU that provides them;
+options to select an FPU that provides them;
for example, @option{-mfpu=neon-fp16 -mfloat-abi=softfp},
in addition to the @option{-mfp16-format} option to select
-a half-precision format.
+a half-precision format.
Language-level support for the @code{__fp16} data type is
independent of whether GCC generates code using hardware floating-point
char **foo = (char *[]) @{ "x", "y", "z" @};
@end smallexample
-Compound literals for scalar types and union types are is
+Compound literals for scalar types and union types are
also allowed, but then the compound literal is equivalent
to a cast.
@cindex @code{alloc_size} attribute
The @code{alloc_size} attribute is used to tell the compiler that the
function return value points to memory, where the size is given by
-one or two of the functions parameters. GCC uses this
+one or two of the functions parameters. GCC uses this
information to improve the correctness of @code{__builtin_object_size}.
The function parameter(s) denoting the allocated size are specified by
of the two function arguments specified. Argument numbering starts at
one.
-For instance,
+For instance,
@smallexample
void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)))
attribute also implies ``default'' visibility. It is an error to
explicitly specify any other visibility.
-In previous versions of GCC, the @code{dllexport} attribute was ignored
+In previous versions of GCC, the @code{dllexport} attribute was ignored
for inlined functions, unless the @option{-fkeep-inline-functions} flag
had been used. The default behaviour now is to emit all dllexported
inline functions; however, this can cause object file-size bloat, in
are @code{printf_unlocked} and @code{fprintf_unlocked}.
@xref{C Dialect Options,,Options Controlling C Dialect}.
-For Objective-C dialects, @code{NSString} (or @code{__NSString__}) is
+For Objective-C dialects, @code{NSString} (or @code{__NSString__}) is
recognized in the same context. Declarations including these format attributes
will be parsed for correct syntax, however the result of checking of such format
-strings is not yet defined, and will not be carried out by this version of the
+strings is not yet defined, and will not be carried out by this version of the
compiler.
The target may also provide additional types of format checks.
synonyms, and cause the compiler to always call
the function by first loading its address into a register, and then using
the contents of that register. The @code{near} attribute has the opposite
-effect; it specifies that non-PIC calls should be made using the more
+effect; it specifies that non-PIC calls should be made using the more
efficient @code{jal} instruction.
@item malloc
On MIPS targets, you can use the @code{mips16} and @code{nomips16}
function attributes to locally select or turn off MIPS16 code generation.
-A function with the @code{mips16} attribute is emitted as MIPS16 code,
-while MIPS16 code generation is disabled for functions with the
-@code{nomips16} attribute. These attributes override the
+A function with the @code{mips16} attribute is emitted as MIPS16 code,
+while MIPS16 code generation is disabled for functions with the
+@code{nomips16} attribute. These attributes override the
@option{-mips16} and @option{-mno-mips16} options on the command line
-(@pxref{MIPS Options}).
+(@pxref{MIPS Options}).
When compiling files containing mixed MIPS16 and non-MIPS16 code, the
preprocessor symbol @code{__mips16} reflects the setting on the command line,
@cindex function without a prologue/epilogue code
Use this attribute on the ARM, AVR, MCORE, RX and SPU ports to indicate that
the specified function does not need prologue/epilogue sequences generated by
-the compiler. It is up to the programmer to provide these sequences. The
-only statements that can be safely included in naked functions are
+the compiler. It is up to the programmer to provide these sequences. The
+only statements that can be safely included in naked functions are
@code{asm} statements that do not have operands. All other statements,
-including declarations of local variables, @code{if} statements, and so
-forth, should be avoided. Naked functions should be used to implement the
+including declarations of local variables, @code{if} statements, and so
+forth, should be avoided. Naked functions should be used to implement the
body of an assembly function, while allowing the compiler to construct
the requisite function declaration for the assembler.
@item save_volatiles
@cindex save volatile registers on the MicroBlaze
Use this attribute on the MicroBlaze to indicate that the function is
-an interrupt handler. All volatile registers (in addition to non-volatile
-registers) will be saved in the function prologue. If the function is a leaf
-function, only volatiles used by the function are saved. A normal function
-return is generated instead of a return from interrupt.
+an interrupt handler. All volatile registers (in addition to non-volatile
+registers) will be saved in the function prologue. If the function is a leaf
+function, only volatiles used by the function are saved. A normal function
+return is generated instead of a return from interrupt.
@item section ("@var{section-name}")
@cindex @code{section} function attribute
in an @code{__attribute__} will still only provide you with 8 byte
alignment. See your linker documentation for further information.
-The @code{aligned} attribute can also be used for functions
+The @code{aligned} attribute can also be used for functions
(@pxref{Function Attributes}.)
@item cleanup (@var{cleanup_function})
Three attributes currently are defined for PowerPC configurations:
@code{altivec}, @code{ms_struct} and @code{gcc_struct}.
-For full documentation of the @code{ms_struct} and @code{gcc_struct}
+For full documentation of the @code{ms_struct} and @code{gcc_struct}
attributes please see the documentation in @ref{i386 Type Attributes}.
The @code{altivec} attribute allows one to declare AltiVec vector data
In this (inefficient) example, the @code{frob} instruction sets the
carry bit to indicate an error. The @code{jc} instruction detects
-this and branches to the @code{error} label. Finally, the output
+this and branches to the @code{error} label. Finally, the output
of the @code{frob} instruction (@code{%r5}) is stored into the memory
for variable @code{y}, which is later read by the @code{return} statement.
The normal code path consists of a single @code{nop} instruction.
However, we record the address of this @code{nop} together with the
address of a label that calls the @code{trace} function. This allows
-the @code{nop} instruction to be patched at runtime to be an
+the @code{nop} instruction to be patched at runtime to be an
unconditional branch to the stored label. It is assumed that an
optimizing compiler will move the labeled block out of line, to
optimize the fall through path from the @code{asm}.
@end deftypefn
+@deftypefn {Built-in Function} void *__builtin_assume_aligned (const void *@var{exp}, size_t @var{align}, ...)
+This function returns its first argument, and allows the compiler
+to assume that the returned pointer is at least @var{align} bytes
+aligned. This built-in can have either two or three arguments,
+if it has three, the third argument should have integer type, and
+if it is non-zero means misalignment offset. For example:
+
+@smallexample
+void *x = __builtin_assume_aligned (arg, 16);
+@end smallexample
+
+means that the compiler can assume x, set to arg, is at least
+16 byte aligned, while:
+
+@smallexample
+void *x = __builtin_assume_aligned (arg, 32, 8);
+@end smallexample
+
+means that the compiler can assume for x, set to arg, that
+(char *) x - 8 is 32 byte aligned.
+@end deftypefn
+
@deftypefn {Built-in Function} void __builtin___clear_cache (char *@var{begin}, char *@var{end})
This function is used to flush the processor's instruction cache for
the region of memory between @var{begin} inclusive and @var{end}
significant bit position. If @var{x} is 0, the result is undefined.
@end deftypefn
+@deftypefn {Built-in Function} int __builtin_clrsb (int x)
+Returns the number of leading redundant sign bits in @var{x}, i.e. the
+number of bits following the most significant bit which are identical
+to it. There are no special cases for 0 or other values.
+@end deftypefn
+
@deftypefn {Built-in Function} int __builtin_popcount (unsigned int x)
Returns the number of 1-bits in @var{x}.
@end deftypefn
@code{unsigned long}.
@end deftypefn
+@deftypefn {Built-in Function} int __builtin_clrsbl (long)
+Similar to @code{__builtin_clrsb}, except the argument type is
+@code{long}.
+@end deftypefn
+
@deftypefn {Built-in Function} int __builtin_popcountl (unsigned long)
Similar to @code{__builtin_popcount}, except the argument type is
@code{unsigned long}.
@code{unsigned long long}.
@end deftypefn
+@deftypefn {Built-in Function} int __builtin_clrsbll (long long)
+Similar to @code{__builtin_clrsb}, except the argument type is
+@code{long long}.
+@end deftypefn
+
@deftypefn {Built-in Function} int __builtin_popcountll (unsigned long long)
Similar to @code{__builtin_popcount}, except the argument type is
@code{unsigned long long}.
The following built-in functions map to the respective machine
instruction, i.e. @code{nop}, @code{sei}, @code{cli}, @code{sleep},
@code{wdr}, @code{swap}, @code{fmul}, @code{fmuls}
-resp. @code{fmulsu}. The latter three are only available if the AVR
-device actually supports multiplication.
+resp. @code{fmulsu}. The three @code{fmul*} built-ins are implemented
+as library call if no hardware multiplier is available.
@smallexample
void __builtin_avr_nop (void)
__float128 __builtin_copysignq (__float128, __float128)
@end smallexample
+The following built-in function is always available.
+
+@table @code
+@item void __builtin_ia32_pause (void)
+Generates the @code{pause} machine instruction with a compiler memory
+barrier.
+@end table
+
The following floating point built-in functions are made available in the
64-bit mode.
@node Darwin Format Checks
@subsection Darwin Format Checks
-Darwin targets support the @code{CFString} (or @code{__CFString__}) in the format
+Darwin targets support the @code{CFString} (or @code{__CFString__}) in the format
attribute context. Declarations made with such attribution will be parsed for correct syntax
and format argument types. However, parsing of the format string itself is currently undefined
-and will not be carried out by this version of the compiler.
+and will not be carried out by this version of the compiler.
Additionally, @code{CFStringRefs} (defined by the @code{CoreFoundation} headers) may
also be used as format arguments. Note that the relevant headers are only likely to be
For compatibility with the Solaris and Tru64 UNIX system headers, GCC
supports two @code{#pragma} directives which change the name used in
-assembly for a given declaration. @code{#pragma extern_prefix} is only
-available on platforms whose system headers need it. To get this effect
+assembly for a given declaration. @code{#pragma extern_prefix} is only
+available on platforms whose system headers need it. To get this effect
on all platforms supported by GCC, use the asm labels extension (@pxref{Asm
Labels}).
#undef X
#define X -1
#pragma pop_macro("X")
-int x [X];
+int x [X];
@end smallexample
In this example, the definition of X as 1 is saved by @code{#pragma
false. Otherwise if @code{__has_trivial_assign (type)} is true then the trait
is true, else if @code{type} is a cv class or union type with copy assignment
operators that are known not to throw an exception then the trait is true,
-else it is false. Requires: @code{type} shall be a complete type,
+else it is false. Requires: @code{type} shall be a complete type,
(possibly cv-qualified) @code{void}, or an array of unknown bound.
@item __has_nothrow_copy (type)
If @code{__has_trivial_constructor (type)} is true then the trait is
true, else if @code{type} is a cv class or union type (or array
thereof) with a default constructor that is known not to throw an
-exception then the trait is true, else it is false. Requires:
-@code{type} shall be a complete type, (possibly cv-qualified)
+exception then the trait is true, else it is false. Requires:
+@code{type} shall be a complete type, (possibly cv-qualified)
@code{void}, or an array of unknown bound.
@item __has_trivial_assign (type)
false. Otherwise if @code{__is_pod (type)} is true then the trait is
true, else if @code{type} is a cv class or union type with a trivial
copy assignment ([class.copy]) then the trait is true, else it is
-false. Requires: @code{type} shall be a complete type, (possibly
+false. Requires: @code{type} shall be a complete type, (possibly
cv-qualified) @code{void}, or an array of unknown bound.
@item __has_trivial_copy (type)
-If @code{__is_pod (type)} is true or @code{type} is a reference type
+If @code{__is_pod (type)} is true or @code{type} is a reference type
then the trait is true, else if @code{type} is a cv class or union type
with a trivial copy constructor ([class.copy]) then the trait
is true, else it is false. Requires: @code{type} shall be a complete
has no non-static data members, or all non-static data members, if
any, are bit-fields of length 0, and @code{type} has no virtual
members, and @code{type} has no virtual base classes, and @code{type}
-has no base classes @code{base_type} for which
+has no base classes @code{base_type} for which
@code{__is_empty (base_type)} is false. Requires: @code{type} shall
be a complete type, (possibly cv-qualified) @code{void}, or an array
of unknown bound.
If @code{type} is a cv union type ([basic.compound]) the trait is
true, else it is false.
+@item __underlying_type (type)
+The underlying type of @code{type}. Requires: @code{type} shall be
+an enumeration type ([dcl.enum]).
+
@end table
@node Java Exceptions
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