Re: [coreutils] Re: [PATCH 2/2] stat: print timestamps to full resolution

[Jim Meyering]

Jim Meyering wrote:

> Jim Meyering wrote:
>
>> Eric Blake wrote:
>>
>>> On 10/21/2010 08:09 AM, Andreas Schwab wrote:
>>>> Eric Blake<address@hidden>  writes:
>>>>
>>>>> On 10/21/2010 03:22 AM, Andreas Schwab wrote:
>>>>>>
>>>>>>
>>>>>> Jim Meyering<address@hidden>   writes:
>>>>>>
>>>>>>> And besides, with coreutils-8.6 already released, reverting the
>>>>>>> change is no longer an option.
>>>>>>
>>>>>> Why?  I'm pretty sure more breakage will pop up over time.
>>>>>
>>>>> How would you propose 'fixing' it?
>>>>
>>>> Add a flag character, eg. %.X.
>>>
>>> %.X is no good, since we already support %.1X (that is, all printf()
>>> flags should keep their existing printf() meaning). But Jim's proposal
>>> of %:X for extended stat info, especially given how date already
>>> supports %:z for extended timezone formatting, makes sense to me.  In
>>> fact, %.3:X might be a nice way to request that the result be
>>> displayed in milliseconds, although Jim's proof of concept patch
>>> didn't cover that aspect.
>>
>> An alternative would be to leave %X, %Y, etc. as the only
>> operators that print seconds-since-epoch, and let the new %:X
>> print the nanoseconds part of the associated time.
>>
>> Then, to get full seconds.nanoseconds, you'd use a format like %X.%:X
>> and if you want only milliseconds, you'd use %X.%3.3:X
>
> Oops.
> I forgot to zero-pad.  Otherwise, with < 100,000,000ns in the first
> case or < 100 in the 2nd, and the above would print invalid numbers.
>
> This is the right way:
>
>   To get full seconds.nanoseconds, you'd use a format like %X.%0:X
>   and if you want only milliseconds, you'd use %X.%03.3:X

A possible disadvantage of using this approach is that the naive
implementation would perform truncation.  I.e., using a format of
"%X.%3.3:X", a time of N.100999999 would be truncated to N.100

I'm inclined to say:
If you care, don't truncate in the first place, or use
another tool, e.g., printf, to format the floating point number.