Tools for dealing with limited precision

[aarchiba]

As we see in #1389, users can miss or ignore the "limited precision" warning when trying to run PINT with 64-bit longdouble values. This PR tries to make PINT run less badly and signal more loudly in this setting.

• The test suite will not run and will emit an error message about precision.
• pint.simulation will make fake TOAs but only good to a few microseconds.
• Functions that require full precision to run can call require_longdouble_precision() to do the test and get an informative exception. I haven't identified any such functions yet (do Fitters work okay, for some values of "okay"?)

I would appreciate additional testing in a 64-bit-only environment (M1 macs, Windows MSVC).

[aarchiba]

In particular, the test suite should refuse to run at all, with a message about precision. I'd appreciate if someone could comment out the line in conftest.py and see what happens when it tries to run the test suite - are there functions where catastrophe occurs and we need to use require_longdouble_precision()?

[aarchiba]

Longer-term, we could go through and flag which tests require full precision and disable running of those tests on low-precision machines.

[paulray]

I tried this on my M1 Mac and it works as advertised. make test fails with a useful error message and the Simulate_and_make_MassMass.py script now runs fine. It warns of limited precision in the first cell, but otherwise seems to work great. This seems good. We definitely do want to make sure that there are plenty of warnings when running dangerous things without extended precision, but much stuff will work just fine.

[paulray]

Typo

[codecov]

Codecov Report

Merging #1392 (6fbc3e6) into master (0d6aeaf) will decrease coverage by 0.00%.
The diff coverage is 58.33%.

@@            Coverage Diff             @@
##           master    #1392      +/-   ##
==========================================
- Coverage   62.25%   62.24%   -0.01%     
==========================================
  Files          89       89              
  Lines       20267    20278      +11     
  Branches     3653     3657       +4     
==========================================
+ Hits        12617    12623       +6     
- Misses       6860     6862       +2     
- Partials      790      793       +3     

Impacted Files	Coverage Δ
src/pint/pulsar_mjd.py	77.31% <ø> (ø)
src/pint/simulation.py	78.14% <40.00%> (-1.45%)	⬇️
src/pint/utils.py	57.24% <71.42%> (+0.17%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.