mpn_gcd[ext] interface details (was: Re: Cofactor canonicalisation of mpn_gcdext)

[Niels Möller]

nisse at lysator.liu.se (Niels Möller) writes:

> I've tried to clarify the mpz_gcdext documentation now. Feel free to
> double check that the conditions on S and T make sense (including the
> borderline cases where one or both inputs are zero). I also edited the
> description of mpz_gcd, to document that we define gcd(0,0) = 0.

And what about normalization of the inputs? The mpn_gcdext documentation
says nothing about normalization. The documentation for mpn_gcd says
that both inputs must be normalized.

I think the actual requirements for both functions are something like

  * an < bn is not allowed

  * if an == bn, then at least one of a or b must be normalized.

  * if an > bn, then b must be normalized

In particular, a > b seems not to be necessary in all cases.

What should the documented requirements be?

Regards,
/Niels

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