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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Long double folding for powerpc target shows apparent underflow despite representable result"
href="http://llvm.org/bugs/show_bug.cgi?id=20682">20682</a>
</td>
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<th>Summary</th>
<td>Long double folding for powerpc target shows apparent underflow despite representable result
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Frontend
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hstong@ca.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>PPC double-double has variable precision and it is generally possible to add
extremely small numbers (e.g., double denorm_min()) to a value which is exactly
representable in a single double without underflow.
### SOURCE:
$ cat ppcLdbl.cc
// fails if A and B differ by at least LDBL_MANT_DIG (106),
// a fixed value not representative of the format
#define A 968
#define B 1074
#define LDBL_VAL2( X ) 0x1p- ## X ## L;
#define LDBL_VAL( X ) LDBL_VAL2( X )
constexpr long double ld0 = LDBL_VAL( A );
constexpr long double ld = ld0 + LDBL_VAL( B );
typedef char chk[ld == ld0 ? -1 : 1];
### COMPILER INVOCATION AND OUTPUT:
$ clang -cc1 -triple powerpc64-unknown-linux-gnu -std=c++11 -x c++ ppcLdbl.cc
ppcLdbl.cc:11:18: error: 'chk' declared as an array with a negative size
typedef char chk[ld == ld0 ? -1 : 1];
^~~~~~~~~~~~~~~~~~
1 error generated.
### EXPECTED OUTPUT:
No errors.
### COMPILER VERSION INFO:
$ clang -target powerpc64-unknown-linux-gnu -v
clang version 3.5.0 (trunk 214060)
Target: powerpc64-unknown-linux-gnu
Thread model: posix</pre>
</div>
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