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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [PATCH] Recording surface ink extents: difference between two fixed point numbers may overflow before conversion to double"
href="https://bugs.freedesktop.org/show_bug.cgi?id=84952">84952</a>
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<th>Summary</th>
<td>[PATCH] Recording surface ink extents: difference between two fixed point numbers may overflow before conversion to double
</td>
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<th>Product</th>
<td>cairo
</td>
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<th>Version</th>
<td>1.12.16
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
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<th>Component</th>
<td>general
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<th>Assignee</th>
<td>chris@chris-wilson.co.uk
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<th>Reporter</th>
<td>cmantunes@gmail.com
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<th>QA Contact</th>
<td>cairo-bugs@cairographics.org
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<pre>Created <span class=""><a href="attachment.cgi?id=107759" name="attach_107759" title="Patch fixes fixed-point overflow bug on recording-surface">attachment 107759</a> <a href="attachment.cgi?id=107759&action=edit" title="Patch fixes fixed-point overflow bug on recording-surface">[details]</a></span>
Patch fixes fixed-point overflow bug on recording-surface
Recording surface may return incorrect result for ink extents when, for
example, it is created unbounded. This is due to a bug in the conversion of a
difference from fixed to floating point. The code for
cairo_recording_surface_ink_extents reads at some point:
*width = _cairo_fixed_to_double (bbox.p2.x - bbox.p1.x);
*height = _cairo_fixed_to_double (bbox.p2.y - bbox.p1.y);
The "solution" (short of getting rid of fixed point altogether) is to change
this to:
*width = _cairo_fixed_to_double (bbox.p2.x) - _cairo_fixed_to_double
(bbox.p1.x);
*height = _cairo_fixed_to_double (bbox.p2.y) - _cairo_fixed_to_double
(bbox.p1.y);
This was tested on MSYS2/MinGW64 and indeed it works as expected.
Attached, you'll find the simple patch. It works against 1.12.16 but the bug is
still present on HEAD.
Thanks!</pre>
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