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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - False positive division by zero"
href="https://bugs.llvm.org/show_bug.cgi?id=39239">39239</a>
</td>
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<tr>
<th>Summary</th>
<td>False positive division by zero
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>6.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Static Analyzer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dcoughlin@apple.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>benbuck@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>To reproduce:
$ cat false_div_zero.c
int false_div_zero(int size, int nitems) {
int len = nitems * size;
if (size && ((len / size) != nitems))
return 0;
return len ? (len / size) : 0;
}
$ clang --analyze false_div_zero.c
false_div_zero.c:5:23: warning: Division by zero
return len ? (len / size) : 0;
~~~~^~~~~~
1 warning generated.
The analyzer seems to assume on line 3 that size is zero, and on line 5 that
len is not zero. However, if size is zero on line 2, then len should also be
zero.
Please note that this reproduction case is a very simplified version of the
relevant part of the gzfwrite() implementation in gzwrite.c from zlib.</pre>
</div>
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