[Python-Dev] PEP 410 (Decimal timestamp): the implementation is ready for a review

[Antoine Pitrou]

Le jeudi 16 février 2012 à 14:20 +0100, Victor Stinner a écrit :
> > If I run your snippet and inspect modification times using `stat`, the
> > difference is much smaller (around 10 ns, not 1 ms):
> >
> > $ stat test | \grep Modify
> > Modify: 2012-02-16 13:51:25.643597139 +0100
> > $ stat test2 | \grep Modify
> > Modify: 2012-02-16 13:51:25.643597126 +0100
> 
> The loss of precision is not constant: it depends on the timestamp value.

Well, I've tried several times and I can't reproduce a 1 ms difference.

> The loss of precision is between 1 ms and 4 us.

It still looks fishy to me. IEEE doubles have a 52-bit mantissa. Since
the integral part of a timestamp takes 32 bits or less, there are still
20 bits left for the fractional part: which allows for at least a 1 µs
precision (2**20 ~= 10**6). A 1 ms precision loss looks like a bug.

Regards

Antoine.