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4.2.6 Modification time of source code files<br />
4.2 Ranking<br />
In general, newer source code is more interesting than old source code. Either the code was<br />
modified to fix a bug, in which case the user is interested in obtaining the latest version of<br />
the code with as many bugfixes as possible. Or the code was written more recently, meaning<br />
that it is more relevant to the user because it solves a current problem.<br />
In <strong>Debian</strong> and Linux in general, there are three different timestamps for each file: The access<br />
time (atime), the change time (ctime) and the modification time (mtime). The difference<br />
between change time and modification time is that changes to the inode (permissions or<br />
owner for example) are recorded in the former, while the latter only gets set when the actual<br />
file contents are modified.<br />
One concern with using the mtimes of individual files within a source package is that —<br />
due to packaging mechanisms — the mtimes might be set to the time at which the package<br />
was created, rendering them useless for our purpose. To determine whether this effect has a<br />
measurable impact, for each source package the following analysis was run: Find each file<br />
within the source package which ends in .c or .h (a quick heuristic for recognizing a portion<br />
of our source code), then calculate the difference between each file’s mtime and the package’s<br />
mtime. For each source package, the average difference was stored.<br />
This analysis can be expressed with the following formula (with f being the list of files for<br />
each source package s):<br />
Amount of source packages<br />
0 10 20 30 40 50 60<br />
ds =<br />
�<br />
f |mtime(f) − mtime(s)|<br />
|f|<br />
mtime difference<br />
0 20000 40000 60000 80000<br />
Average mtime difference [s]<br />
Figure 4.1: Average mtime difference between the source package and its .c or .h files<br />
A little over 60 packages (0.6 % of all analyzed source packages) have an average mtime<br />
difference near zero. In these cases, mtime is not a good ranking factor, but 60 packages is a<br />
negligible number.<br />
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