mpn_perfpow: do we need a special GCD for mp_bitcnt_t?

[Torbjörn Granlund]

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

  > Using mpn_remove does not solve a little issue, the mixed use of
  > mp_bitcnt_t and mp_limb_t. When a prime factor is removed from the
  > examined number, the exponent is returned as mp_bitcnt_t, the returned
  > value is then casted to mp_limb_t, because we need the GCD of the
  > exponents and mpn_gcd_1 wants limbs.
  
  And when can there be a problem? If the mp_limb_t type is smaller than
  mp_bitcnt_t? I guess that could happen if configuring with artificially
  small limbs, but not otherwise?
  
I am not aware of any configutations where mp_limb_t is the smaller of
the two.  But I feel bothered by type mixing such as this.

I mean to integrate Per Olofsson's mini-limb patches at some point in
the not very distant future.  They require separation in a few more
places where we (ab)use mp_limb_t for conceptually other data types.

  Vagely related: We chould have an mpn_gcd_11 function, accepting two
  limb-size arguments.
  
Which would then be in assembly.  This would obsolete the many mpn_gcd_1
implementations, I think.

Torbjörn
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