__builtin_object_size(3) [netbsd man page]

__BUILTIN_OBJECT_SIZE(3)				   BSD Library Functions Manual 				  __BUILTIN_OBJECT_SIZE(3)

NAME

     __builtin_object_size -- return the size of the given object

SYNOPSIS

     size_t
     __builtin_object_size(void *ptr, int type);

DESCRIPTION

     The __builtin_object_size() function is a gcc(1) built-in function that returns the size of the ptr object if known at compile time and the
     object does not have any side effects.

RETURN VALUES

     If the size of the object is not known or it has side effects the __builtin_object_size() function returns:

	   (size_t)-1  for type 0 and 1.

	   (size_t)0   for type 2 and 3.

     If the size of the object is known, then the __builtin_object_size() function returns the maximum size of all the objects that the compiler
     knows that they can be pointed to by ptr when type & 2 == 0, and the minimum size when type & 2 != 0.

SEE ALSO

     gcc(1), __builtin_return_address(3), attribute(3), ssp(3)

HISTORY

     The __builtin_object_size() appeared in GCC 4.1.

CAVEATS

     This is a non-standard, compiler-specific extension.

BSD
								 December 19, 2010							       BSD

__BUILTIN_CONSTANT_P(3) 				   BSD Library Functions Manual 				   __BUILTIN_CONSTANT_P(3)

NAME

     __builtin_constant_p -- GNU extension to determine compile time constants

SYNOPSIS

     int
     __builtin_constant_p(value);

DESCRIPTION

     The __builtin_constant_p() is a GNU extension for determining whether a value is known to be constant at compile time.  The function is
     closely related to the concept of ``constant folding'' used by modern optimizing compilers.

     If the value is known to be a compile-time constant, a value 1 is returned.  If __builtin_constant_p() returns 0, the value is not a compile-
     time constant in the sense that gcc(1) was unable to determine whether the value is constant or not.

EXAMPLES

     A typical example of the use of __builtin_constant_p() involves a situation where it may be desirable to fold the computation if it involves
     a constant, but a function call is needed otherwise.  For instance, bswap16(3) is defined in NetBSD as:

	   #define bswap16(x) 
		   (__builtin_constant_p((x)) ? 
		    __byte_swap_u16_constant(x) : __BYTE_SWAP_U16_VARIABLE(x))

SEE ALSO

     gcc(1), __builtin_object_size(3), __builtin_return_address(3)

CAVEATS

     This is a non-standard, compiler-specific extension.

BSD
								 December 19, 2010							       BSD