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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - confusing return from _mm_extract_epi8() in smmintrin.h"
href="http://llvm.org/bugs/show_bug.cgi?id=17300">17300</a>
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<th>Summary</th>
<td>confusing return from _mm_extract_epi8() in smmintrin.h
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.3
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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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>P
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>vvsed@hotmail.com
</td>
</tr>
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<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>_mm_extract_epi8() function in smmintrin.h returns unsigned char instead of
int.
It is confusing because the corresponding PEXTRB instruction returns ***zero
extended*** int/__int64 value.
In smmintrin.h of GNU C "(unsigned char)" is redundant:
extern __inline int __attribute__((__gnu_inline__, __always_inline__,
__artificial__))
_mm_extract_epi8 (__m128i __X, const int __N)
{
return (unsigned char) __builtin_ia32_vec_ext_v16qi ((__v16qi)__X, __N);
}
While smmintrin.h of Intel C contains:
extern int __ICL_INTRINCC _mm_extract_epi8 (__m128i, const int);
The corresponding instruction is:
PEXTRB reg/m8, xmm2, imm8
It's Intel description:
Extract a byte integer value from xmm2 at the
source byte offset specified by imm8 into reg
or m8. ***The upper bits of r32 or r64 are zeroed***.</pre>
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