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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __gcc_qadd produces spurious infinity"
href="https://bugs.llvm.org/show_bug.cgi?id=49131">49131</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>__gcc_qadd produces spurious infinity
</td>
</tr>
<tr>
<th>Product</th>
<td>compiler-rt
</td>
</tr>
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<th>Version</th>
<td>11.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>compiler-rt
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>bbaren@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=24511" name="attach_24511" title="minimal example">attachment 24511</a> <a href="attachment.cgi?id=24511&action=edit" title="minimal example">[details]</a></span>
minimal example
__gcc_qadd, which adds two double-double long doubles on POWER, can incorrectly
return infinity instead of a finite result:
$ cat ldbl.c
extern int printf(const char* restrict, ...);
int main() {
long double a = -0x1.1e282e024debdb875f47f6c85p+1021L;
printf("%Le\n", a + 0x1.fffffffffffff7ffffffffffff8p+1023L);
}
$ clang -Wall -Wextra -O0 -rtlib=compiler-rt -o ldbl ldbl.c
$ ./ldbl
inf
The two operands in this case are approximately -2.5e+307 and 1.8e+308; each
has a valid and finite double-double representation, and adding them should
produce another finite one. (In this case, the correct answer is about
1.5+308.)
I originally discovered this using Debian’s clang 11.0.1-2, but it’s also
present in non-Debian builds.
GCC produces the correct answer for this computation, though only when
optimizations are enabled (see
<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99048">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99048</a>).</pre>
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