Precision issue when adding 0 seconds to a Time

I’m running into a weird issue on 32-bit systems

>>> from astropy.time import Time
>>> from astropy import units as u
>>> t = Time('2016-03-22T12:30:31.000')
>>> t == t
True
>>> t + 0 * u.s == t
False

It looks like jd2 is being modified even though the offset is 0:

>>> t.jd1
2457470.0
>>> t.jd2
0.021192129629629575
>>> (t + 0 * u.s).jd1
2457470.0
>>> (t + 0 * u.s).jd2
0.02119212962962962

To reproduce, do this in the astropy repo:

docker run -v $PWD:/repo -it quay.io/pypa/manylinux1_i686 /bin/bash

then this in the docker image shell:

/opt/python/cp36-cp36m/bin/pip install numpy scipy "pytest<3.7" pytest-astropy pytest-xdist Cython jinja2
/opt/python/cp36-cp36m/bin/python setup.py develop
/opt/python/cp36-cp36m/bin/python

then run the code above.

[lrm25]

Hi. Hacktoberfest brought me here. I just reproduced this. I’ll take a look at it.

[mhvk]

Looking back through the text here, the bug was for a specific 32-bit version, but more generally represented UTC and TAI not perfectly round-tripping. I’ll close this in favour of #6970, which deals with that as well (and a bit more generally).