sec_invert performance

[Torbjorn Granlund]

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

  So if you know that the modulo is prime (or has some other type of known
  factorization), using powm actually beats sec_invert for sizes up to 6
  limbs.
  
Assuming CRT application is for free, at least.

  I still puzzled why the ratio between sec_invert and gcdext doesn't
  approach some constant (I'd expect the ratio to start growing again for
  sizes above the threshold for subquadratic gcdext).
  
I don't find the ratio strange, it seems constant within reasonable
fluctuations.

All linear-time functions really take Bn+C time, and quadratic-time
functions take An²+Bn+C, of course.  If the sec_invert function has
small B and/or C while gcdext has larger B and/or C, then the observed
pattern seem even more reasonable.  Do you agree?

Torbjörn
Please encrypt, key id 0xC8601622