[PROJ] spilhaus regresssion test failures

[Greg Troxel]

Greg Troxel via PROJ <proj at lists.osgeo.org> writes:

> I looked at that code, and it jumped out at me that are abs() was used,
> which is a C function, not C++, and is integer only.
>
> With this patch (to 9.6.0), I get a pass:
>
> --- src/latitudes.cpp.~1~       2025-03-13 10:31:27.000000000 -0400
> +++ src/latitudes.cpp   2025-05-04 14:23:04.656697860 -0400
> @@ -58,7 +58,7 @@
>              2 * atan(taninit *
>                       std::pow(((1 + esinphi) / (1 - esinphi)), (e / 2))) -
>              0.5 * M_PI;
> -        if (abs(new_phi - phi) < threshold) {
> +        if (std::abs(new_phi - phi) < threshold) {
>              phi = new_phi;
>              break;
>          }
>
> Interesting that this only causes trouble with spilhaus, at least as far
> as tests catch it.

Which do we want to do:

  A) pullup the PR #4446 (@cffk aux latitude cleanup) to the 9.6 release
     branch

  B) Decide not to pullup, and change abs to std::abs?

If B, I can make a PR, but if we're going to do A, that isn't useful.

FWIW, I would tend to lean to A, as a grand simplification, but as I
read the discussion it's considered over the line to feature vs bugfix
and I can certainly see that point of view.