mpn_perfpow: do we need a special GCD for mp_bitcnt_t?

[Torbjörn Granlund]

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

  A compromise might be to add something like
  
    #if MP_BITCNT_T_MAX < MP_LIMB_T_MAX
    #error mp_limb_t too small !?
    #endif
  
  close to the code which assigns an mp_bitcnt_t to an mp_limb_t. At
  least, this documents the assumption made. (Except that I don't think
  MP_BITCNT_T_MAX exists, and the common way of writing it as
  ~(mp_bitcnt_t) 0 won't work in a preprocessor conditional).
  
In the Pers alimbs branch, I had to add lots of those macros.

  Another alternative might be to define a gcd_11 function taking
  uintmax_t arguments. However, I don't really trust uintmax_t; it's
  specified in essentially the same way as "unsigned long long" was
  originally specified, but long is often not the largest type in current
  C compilers.
  
Let's not involve uintmax_t.  A plain conditional, explicit casts in any
call, and a fall-back function such as gcd_bitcnt would be fine.

Or even cleaner, use gcd_bitcnt always and have the conditionals there.


Torbjörn
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