mpn_sqrtrem2

[paul zimmermann]

   Hi,

the attached file contains a new version (mpn_sqrtrem2_new) of mpn_sqrtrem2
for 64-bit computers. On my computer i5-4590 it runs in about 65 cycles
whereas the gmp-6.1.1 version runs in about 96 cycles.

It uses an auxiliary routine (mpn_rsqrtrem1) which computes a 41-bit
approximation of 1/sqrt(a).

Before I try to adapt those two routines to 32-bit limbs, I'd like someone
to review my code (comments are included).

Paul
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