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<th>Priority</th>
<td>medium
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</tr>
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - difference of non negative enums is never negative"
href="https://bugs.freedesktop.org/show_bug.cgi?id=83295">83295</a>
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<th>Assignee</th>
<td>chris@chris-wilson.co.uk
</td>
</tr>
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<th>Summary</th>
<td>difference of non negative enums is never negative
</td>
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<th>QA Contact</th>
<td>cairo-bugs@cairographics.org
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
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<th>Reporter</th>
<td>sixtysix@inwind.it
</td>
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<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Component</th>
<td>general
</td>
</tr>
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<th>Product</th>
<td>cairo
</td>
</tr></table>
<p>
<div>
<pre>Gcc treats enum with non negative values as unsigned,
so using the difference in a comparison function is
questionable:
<a href="http://cgit.freedesktop.org/cairo/tree/src/cairo-polygon-intersect.c#n794">http://cgit.freedesktop.org/cairo/tree/src/cairo-polygon-intersect.c#n794</a>
for example adding a
assert (a->type - b->type >= 0);
gcc prints
src/cairo-polygon-intersect.c|795 col 15| warning: comparison of unsigned
expression >= 0 is always true [-Wtype-limits]
assert (a->type - b->type >= 0);
this means that three events (START, STOP, INTERSECTION) in the same
place will be potentially each one after each other, making difficult
to understand whether equally located STOP/INTER/START events should be
really processed in that order or not.</pre>
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