Re: [PATCH] compat: helper for detecting unsigned overflow

On Feb 10, 2011, at 4:11 AM, Sverre Rabbelier wrote:

On Thu, Feb 10, 2011 at 10:35, Jonathan Nieder [off-list ref]  
wrote:

quoted

      unsigned_add_overflows(a, b)

quoted

Define such a macro, expanding roughly to ((a) < UINT_MAX - (b)).
Because the expansion uses each argument only once outside of  
sizeof()
expressions, it is safe to use with arguments that have side effects.

quoted

+#define unsigned_add_overflows(a, b) \
+    ((b) > maximum_unsigned_value_of_type(a) - (a))

I'm confused, you say you won't use it twice, and then you do use it  
twice?

The author is asserting that maximum_unsigned_value_of_type() is a  
function of sizeof a, which would have no runtime effect.

Josh