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14.6 Layout of Source Language Data Types

These macros define the sizes and other characteristics of the standard basic data types used in programs being compiled. Unlike the macros in the previous section, these apply to specific features of C and related languages, rather than to fundamental aspects of storage layout.

— Macro: INT_TYPE_SIZE

A C expression for the size in bits of the type int on the target machine. If you don't define this, the default is one word.

— Macro: SHORT_TYPE_SIZE

A C expression for the size in bits of the type short on the target machine. If you don't define this, the default is half a word. (If this would be less than one storage unit, it is rounded up to one unit.)

— Macro: LONG_TYPE_SIZE

A C expression for the size in bits of the type long on the target machine. If you don't define this, the default is one word.

— Macro: ADA_LONG_TYPE_SIZE

On some machines, the size used for the Ada equivalent of the type long by a native Ada compiler differs from that used by C. In that situation, define this macro to be a C expression to be used for the size of that type. If you don't define this, the default is the value of LONG_TYPE_SIZE.

— Macro: LONG_LONG_TYPE_SIZE

A C expression for the size in bits of the type long long on the target machine. If you don't define this, the default is two words. If you want to support GNU Ada on your machine, the value of this macro must be at least 64.

— Macro: CHAR_TYPE_SIZE

A C expression for the size in bits of the type char on the target machine. If you don't define this, the default is BITS_PER_UNIT.

— Macro: BOOL_TYPE_SIZE

A C expression for the size in bits of the C++ type bool and C99 type _Bool on the target machine. If you don't define this, and you probably shouldn't, the default is CHAR_TYPE_SIZE.

— Macro: FLOAT_TYPE_SIZE

A C expression for the size in bits of the type float on the target machine. If you don't define this, the default is one word.

— Macro: DOUBLE_TYPE_SIZE

A C expression for the size in bits of the type double on the target machine. If you don't define this, the default is two words.

— Macro: LONG_DOUBLE_TYPE_SIZE

A C expression for the size in bits of the type long double on the target machine. If you don't define this, the default is two words.

— Macro: LIBGCC2_LONG_DOUBLE_TYPE_SIZE

Define this macro if LONG_DOUBLE_TYPE_SIZE is not constant or if you want routines in libgcc2.a for a size other than LONG_DOUBLE_TYPE_SIZE. If you don't define this, the default is LONG_DOUBLE_TYPE_SIZE.

— Macro: LIBGCC2_HAS_DF_MODE

Define this macro if neither LIBGCC2_DOUBLE_TYPE_SIZE nor LIBGCC2_LONG_DOUBLE_TYPE_SIZE is DFmode but you want DFmode routines in libgcc2.a anyway. If you don't define this and either LIBGCC2_DOUBLE_TYPE_SIZE or LIBGCC2_LONG_DOUBLE_TYPE_SIZE is 64 then the default is 1, otherwise it is 0.

— Macro: LIBGCC2_HAS_XF_MODE

Define this macro if LIBGCC2_LONG_DOUBLE_TYPE_SIZE is not XFmode but you want XFmode routines in libgcc2.a anyway. If you don't define this and LIBGCC2_LONG_DOUBLE_TYPE_SIZE is 80 then the default is 1, otherwise it is 0.

— Macro: LIBGCC2_HAS_TF_MODE

Define this macro if LIBGCC2_LONG_DOUBLE_TYPE_SIZE is not TFmode but you want TFmode routines in libgcc2.a anyway. If you don't define this and LIBGCC2_LONG_DOUBLE_TYPE_SIZE is 128 then the default is 1, otherwise it is 0.

— Macro: TARGET_FLT_EVAL_METHOD

A C expression for the value for FLT_EVAL_METHOD in float.h, assuming, if applicable, that the floating-point control word is in its default state. If you do not define this macro the value of FLT_EVAL_METHOD will be zero.

— Macro: WIDEST_HARDWARE_FP_SIZE

A C expression for the size in bits of the widest floating-point format supported by the hardware. If you define this macro, you must specify a value less than or equal to the value of LONG_DOUBLE_TYPE_SIZE. If you do not define this macro, the value of LONG_DOUBLE_TYPE_SIZE is the default.

— Macro: DEFAULT_SIGNED_CHAR

An expression whose value is 1 or 0, according to whether the type char should be signed or unsigned by default. The user can always override this default with the options -fsigned-char and -funsigned-char.

— Target Hook: bool TARGET_DEFAULT_SHORT_ENUMS (void)

This target hook should return true if the compiler should give an enum type only as many bytes as it takes to represent the range of possible values of that type. It should return false if all enum types should be allocated like int.

The default is to return false.

— Macro: SIZE_TYPE

A C expression for a string describing the name of the data type to use for size values. The typedef name size_t is defined using the contents of the string.

The string can contain more than one keyword. If so, separate them with spaces, and write first any length keyword, then unsigned if appropriate, and finally int. The string must exactly match one of the data type names defined in the function init_decl_processing in the file c-decl.c. You may not omit int or change the order—that would cause the compiler to crash on startup.

If you don't define this macro, the default is "long unsigned int".

— Macro: PTRDIFF_TYPE

A C expression for a string describing the name of the data type to use for the result of subtracting two pointers. The typedef name ptrdiff_t is defined using the contents of the string. See SIZE_TYPE above for more information.

If you don't define this macro, the default is "long int".

— Macro: WCHAR_TYPE

A C expression for a string describing the name of the data type to use for wide characters. The typedef name wchar_t is defined using the contents of the string. See SIZE_TYPE above for more information.

If you don't define this macro, the default is "int".

— Macro: WCHAR_TYPE_SIZE

A C expression for the size in bits of the data type for wide characters. This is used in cpp, which cannot make use of WCHAR_TYPE.

— Macro: WINT_TYPE

A C expression for a string describing the name of the data type to use for wide characters passed to printf and returned from getwc. The typedef name wint_t is defined using the contents of the string. See SIZE_TYPE above for more information.

If you don't define this macro, the default is "unsigned int".

— Macro: INTMAX_TYPE

A C expression for a string describing the name of the data type that can represent any value of any standard or extended signed integer type. The typedef name intmax_t is defined using the contents of the string. See SIZE_TYPE above for more information.

If you don't define this macro, the default is the first of "int", "long int", or "long long int" that has as much precision as long long int.

— Macro: UINTMAX_TYPE

A C expression for a string describing the name of the data type that can represent any value of any standard or extended unsigned integer type. The typedef name uintmax_t is defined using the contents of the string. See SIZE_TYPE above for more information.

If you don't define this macro, the default is the first of "unsigned int", "long unsigned int", or "long long unsigned int" that has as much precision as long long unsigned int.

— Macro: TARGET_PTRMEMFUNC_VBIT_LOCATION

The C++ compiler represents a pointer-to-member-function with a struct that looks like:

            struct {
              union {
                void (*fn)();
                ptrdiff_t vtable_index;
              };
              ptrdiff_t delta;
            };
     

The C++ compiler must use one bit to indicate whether the function that will be called through a pointer-to-member-function is virtual. Normally, we assume that the low-order bit of a function pointer must always be zero. Then, by ensuring that the vtable_index is odd, we can distinguish which variant of the union is in use. But, on some platforms function pointers can be odd, and so this doesn't work. In that case, we use the low-order bit of the delta field, and shift the remainder of the delta field to the left.

GCC will automatically make the right selection about where to store this bit using the FUNCTION_BOUNDARY setting for your platform. However, some platforms such as ARM/Thumb have FUNCTION_BOUNDARY set such that functions always start at even addresses, but the lowest bit of pointers to functions indicate whether the function at that address is in ARM or Thumb mode. If this is the case of your architecture, you should define this macro to ptrmemfunc_vbit_in_delta.

In general, you should not have to define this macro. On architectures in which function addresses are always even, according to FUNCTION_BOUNDARY, GCC will automatically define this macro to ptrmemfunc_vbit_in_pfn.

— Macro: TARGET_VTABLE_USES_DESCRIPTORS

Normally, the C++ compiler uses function pointers in vtables. This macro allows the target to change to use “function descriptors” instead. Function descriptors are found on targets for whom a function pointer is actually a small data structure. Normally the data structure consists of the actual code address plus a data pointer to which the function's data is relative.

If vtables are used, the value of this macro should be the number of words that the function descriptor occupies.

— Macro: TARGET_VTABLE_ENTRY_ALIGN

By default, the vtable entries are void pointers, the so the alignment is the same as pointer alignment. The value of this macro specifies the alignment of the vtable entry in bits. It should be defined only when special alignment is necessary. */

— Macro: TARGET_VTABLE_DATA_ENTRY_DISTANCE

There are a few non-descriptor entries in the vtable at offsets below zero. If these entries must be padded (say, to preserve the alignment specified by TARGET_VTABLE_ENTRY_ALIGN), set this to the number of words in each data entry.