fast determination of sign of sum

[keith.briggs at bt.com]

I would be grateful for suggestions on these questions:

1.  Given two large mpz_t (say, of order 2^1000000), what is the best
way to determine the sign of their sum?  Is it better just to add them,
or to do several comparisons and sign tests?

2.  If it is better not to add them, is it still better to use the
comparison and sign test method recursively to determine the sign of the
sum of more than two integers?   (In my actual application, there are
four.)

Thanks,
Keith


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