Neon support for mpz_powm/mpz_powm_sec

[Torbjörn Granlund]

Robert Foss <personal at robertfoss.se> writes:

  I was wondering if there are any neon optimizations that are coming
  down the pipeline that are relevant for mpz_powm mpz_powm_sec.
  
  I've done some benchmarking with the current trunk, but armcortexa7
  and armcortexa7neon seem to perform identically.
  
The current repo code uses Neon stuff for just a handful functions, but
the most criticasl functions are done with core register instructions.

We made some tweaks to multiplication quite recently which should help
a7 slightly.
  

-- 
Torbjörn
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