Messages in this thread | | | Subject | Re: [PATCH v2 3/9] bitops: Introduce a more generic BITMASK macro | From | Joe Perches <> | Date | Wed, 16 Oct 2013 23:58:56 -0700 |
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On Thu, 2013-10-17 at 02:30 -0400, Chen Gong wrote: > On Wed, Oct 16, 2013 at 07:59:09PM -0700, Joe Perches wrote: [] > > Maybe add a > > > > BUILD_BUG_ON(__builtin_constant_p(l) && __builtin_constant_p(h) && \ > > (h) < (l)) > > > No, if so, users can't use variables for this macro.
__builtin_constant_p checks for constants
Built-in Function: int __builtin_constant_p (exp) You can use the built-in function __builtin_constant_p to determine if a value is known to be constant at compile-time and hence that GCC can perform constant-folding on expressions involving that value. The argument of the function is the value to test. The function returns the integer 1 if the argument is known to be a compile-time constant and 0 if it is not known to be a compile-time constant. A return of 0 does not indicate that the value is not a constant, but merely that GCC cannot prove it is a constant with the specified value of the -O option.
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