Sorry, I saw this discussion a little late...

The Internet checksum is defined as a 1's-complement sum, so if  the
alternate 0 does not have a special meaning in a protocol, then by
1's-complement arithmetic, 0 == ~0.
        So, it looks to me without the remapping that a valid checksum
may also fail, if it is simply computed in a different way (or on a 
different
architecture) such that one gets 0 and one gets ~0 as un-modified answers.
        Since we're checking for equality on 2's-complement machines,
I think the easiest thing is to still re-map it. Otherwise, instead of 
testing
for 0, we have to test for both 0 and ~0 in the validity checks, right?

        Disclaimer: I've just glanced through the discussion, so maybe
I've misunderstood the point or effect of the patch...

                                                +-DLS

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