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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Probable pessimization in steady_clock"
href="http://llvm.org/bugs/show_bug.cgi?id=16754">16754</a>
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<th>Summary</th>
<td>Probable pessimization in steady_clock
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>MacOS X
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
</td>
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<th>Assignee</th>
<td>hhinnant@apple.com
</td>
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<th>Reporter</th>
<td>mike.marcin@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>There is a comment in chrono.cpp
// MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.
Specialize
// for that case as an optimization.
This comment points to:
steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
static FP fp = init_steady_clock();
return time_point(duration(fp()));
}
Which replaces a double precision multiply with a call through a function
pointer as an optimization.
static
steady_clock::rep
steady_full()
{
static const double factor = compute_steady_factor();
return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
}
vs
static
steady_clock::rep
steady_simplified()
{
return static_cast<steady_clock::rep>(mach_absolute_time());
}</pre>
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</p>
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