mpz reuse test takes too much time

[Torbjörn Granlund]

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

  Actually, in the case of gcdext, there are three result arguments, which
  mustn't overlap with each other.
  
  So there are only 16 cases of valid overlap when all operands are
  provided, and 9 cases of valid overlap when the t argument is NULL.
  
Please check that reuse.c whacks gcdext appropriately.

-- 
Torbjörn
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