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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - std::complex seems to use unsafe floating point math by default"
href="http://llvm.org/bugs/show_bug.cgi?id=22241">22241</a>
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</tr>
<tr>
<th>Summary</th>
<td>std::complex seems to use unsafe floating point math by default
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.4
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++11
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>alex.hultman@strusoft.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Hi.
Consider the following code:
#include <complex>
#include <iostream>
#include <iomanip>
int main()
{
std::complex<double> c(-61.887073591767951,-60.052083270252012);
double a = (1.0 / c).real();
std::cout << std::setprecision(17) << " " << a << std::endl;
}
With g++ and gfortran (with corresponding Fortran code) and Octave (ditto),
this outputs:
-8.3223357032193145 (ends with 45)
However, clang++ outputs:
-0.0083223357032193128 (ends with 28)
The thing is, when compiling with g++ -ffast-math, I get the same as I get in
clang++ (without any optimization or -ffast-math).
So: "g++ -ffast-math complex.cpp" gives the same output as "clang++
complex.cpp"
I'm on Fedora 21 with clang++ --version:
clang version 3.4.2 (tags/RELEASE_34/dot2-final)
Target: x86_64-redhat-linux-gnu
Thread model: posix</pre>
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