Replacing gcd_1 with gcd_11

[Niels Möller]

"Marco Bodrato" <bodrato at mail.dm.unipi.it> writes:

> The current code uses mpn_gcd_1 (up, 2, vp[1]) for the 2:1 case. That
> function perform an initial modular reduction.
>
> Is mpn_gcd_22 (up[1], up[0], 0, v1) as fast as that code?

mpn_gcd_22 will be slower for that case. But I'm not sure if it that is
important. 

We will never reach the 2:1 case with user inputs, since mpn_gcd does an
initial division if u and v are of different limb size. And if we reach
it after one or more iterations of the hgcd/hgcd2 steps, or directly
after the initial division, then I think it's unlikely to have u and v
with bit sizes differing by many bits.

Regards, 
/Niels

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