build: reduce build requirements on gmp and mpfr

[jengelh]

Systems like openSUSE Leap 15.6 have gmp-6.1.2 and mpfr-4.0.2, so I located the minimum viable versions for flint and adjusted configure.ac.

[albinahlback]

I'd rather not have conditional requirements when it comes to versioning.

But more importantly, I believe that if you want to build the development version of FLINT, I think it is reasonable to have recent versions of GMP and MPFR. Both GMP 6.2.1 and MPFR 4.1.0 were released more than four years ago.

[jengelh]

Where do I see that some specific version of flint is development or not?
(The patch was originally made for 3.2.0, just the PR for master out of common practice.)

[albinahlback]

You can see it in the VERSION file.

But, for package managers, I don't see where you would want to distribute a recent version of FLINT without a recent version of GMP and MPFR.

For people wanting to build a recent version of FLINT on an old system, you sort of have to expect that we want you to have a recent version of GMP and MPFR. These are not heavy dependencies, so I think it is reasonable.

[edgarcosta]

@albinahlback , to clarify the discussion:

Does Flint need the new versions?
If not, why should a user not try to build against old versions?

[albinahlback]

We need mpn_zero_p, so we require GMP 6.2.0. And MPFR 4.1.0 is about the same age.

We could switch to flint_mpn_zero_p, but I recall there was something that hindered us from going back to an earlier version of GMP.

[albinahlback]

This is the PR were we made the change: #1591

[edgarcosta]

It looks like you and @fredrik-johansson agreed that requirement of 6.2.0 made sense.
Unless you changed your mind, we can close down this PR.

BTW, looking at flint_mpn_zero_p vs mpn_zero_p the difference seems to be that they start looking at most significant word, while we look at least significant.

MPN_EXTRAS_INLINE
int flint_mpn_zero_p(mp_srcptr x, mp_size_t xsize)
{
    slong i;
    for (i = 0; i < xsize; i++)
    {
        if (x[i])
            return 0;
    }
    return 1;
}

https://github.com/flintlib/flint/blob/main/src/mpn_extras.h#L65-L75

vs

int
mpn_zero_p (mp_srcptr __gmp_p, mp_size_t __gmp_n) __GMP_NOTHROW
{
  /* if (__GMP_LIKELY (__gmp_n > 0)) */
    do {
      if (__gmp_p[--__gmp_n] != 0)
	return 0;
    } while (__gmp_n != 0);
  return 1;
}

https://github.com/gmp-mirror/gmp/blob/master/gmp-h.in#L2184-L2193