roundtrip for proleptic_gregorian calendar wrong for reference dates before Julian/Gregorian transition #189
Description
import cftime as cf
from cftime import DatetimeProlepticGregorian as datetime
dt1 = datetime(2020, 4, 24, 16, 15, 10)
print(dt1)
units='days since -4713-01-01 12:00'
cal='proleptic_gregorian'
print(cf.num2date(cf.date2num(dt1, units, cal), units, cal))
2020-04-24 16:15:10
2020-03-19 16:15:10For this example, it's off by 38 days.
Correct result is obtained if reference date year changed to 1583.