mini-gmp mpz_{get,set}_d not fully compatible with GMP

[Torbjörn Granlund]

Vincent Lefevre <vincent at vinc17.net> writes:

  On 2018-03-12 18:53:37 +0100, Marco Bodrato wrote:
  > double
  > mpz_get_d (const mpz_t u)
  > {
  >   static int c = 0;
  >   static int __initialized = 0;
  > 
  >   if (__initialized != 1) {
  >     c = gmp_tests_dbl_mant_bits ();
  >     *((volatile int *) &__initialized) = 1;
  >   }

  FYI, this is not thread-safe.

I suppose the externally visible store order is not guaranteed to be the
same as the program store order, not even with "volatile".

One variable, declared as volatile, should work fine though.  Of course,
that assumes some value for the variable can be used to represent a
non-initialised state.  For c above, 0 seems to be a useable value as no
floating-point format with zero mantissa bits has yet been invented.

-- 
Torbjörn
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