Re: .LOW_RESOLUTION_TIME

[Eli Zaretskii]

> Date: Tue, 9 Nov 2010 14:26:40 +0330
> From: ali hagigat <address@hidden>
> 
> cp -p src dst
> 
> Since ‘cp -p’ discards the subsecond part of ‘src’’s time stamp, ‘dst’
> is typically slightly older than ‘src’ even when it is up to date.
> The .LOW_RESOLUTION_TIME line causes make to consider ‘dst’ to be up
> to date if its time stamp is at
> the start of the same second that ‘src’’s time stamp is in.
> ----------------------------------------------------------------
> When we used -p , it means preserve time-stamp, so how ‘dst’ is
> typically slightly older than ‘src’ ?

It's a misfeature of (some versions of) `cp': it preserves the time
stamp only to the seconds resolution, and discards the milliseconds
part.  So if the original file was time-stamped 10:25:32.890, the
copied file will have the time-stamp of 10:25:32, which is 890
milliseconds older.

> And concerning the last statement:
> if the time stamp of 'dst' is at the start of the same second that
> ‘src’’s time stamp is in, so the both time-stamps are the same and
> 'dst' is up-to-date, why we need  .LOW_RESOLUTION_TIME to say that
> 'dst' is up-to-date?

Because Make compares time stamps as numbers, including the
milliseconds part.