Add mpz_inp_str to mini-gmp

[Torbjörn Granlund]

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

  That's no big deal for mini-gmp, it's not intended to be used for huge
  numbers, or make a lot of effort to be as efficient. Which of course is
  a judgement call.
  
Reading to a buffer rather than convert on-the-fly makes sense iff
mpz_set_str somehow makes tricks for better performance (such as
clumping characters into limbs to avoid most bignum operations, or using
some o(n^2) algorithm).


-- 
Torbjörn
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