@serhiy.storchaka
> 1580301619906185300/10**9 is more accurate than 1580301619906185300/1e9.

I don't know exactly what `F` represents in your example but here is what I get:

>>> r = 1580301619906185300                                                              
>>> int(r / 10**9 * 10**9) - r                                                           
172
>>> int(r / 1e9 * 10**9) - r                                                             
-84

@vstinner
> I suggest to only document in time.time() is less accurate than time.time_ns().

Sounds good!