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__builtin_constant_p(3) [netbsd man page]

__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

Check Out this Related Man Page

__BUILTIN_RETURN_ADDRESS(3)				   BSD Library Functions Manual 			       __BUILTIN_RETURN_ADDRESS(3)

NAME
__builtin_return_address -- the return address of a function SYNOPSIS
void * __builtin_return_address(unsigned int level); void * __builtin_frame_address(unsigned int level); DESCRIPTION
The __builtin_return_address() is a GNU extension for obtaining the return address of the current function or one of the callers of the cur- rent function. The parameter level specifies the number of frames that should be scanned up in the call stack. A value 0 returns the address of the current function, a value 1 requests the address of the caller of the current function, a value 2 asks for the address of the caller's caller, and so forth. If the top of the call stack has been reached, the function will return 0. Note also that on some architectures it is only possible to determine the address of the current function. In such cases a value 0 is returned. Thus, it is usually safe to only use the value 0 for level. The __builtin_frame_address() behaves similarly, but returns the address of the function frame rather than the return address of the func- tion. SEE ALSO
gcc(1), __builtin_object_size(3) CAVEATS
These are non-standard, compiler-specific extensions. BSD
December 19, 2010 BSD
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