rationale.html
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="align.rationale"></a><a class="link" href="rationale.html" title="Rationale">Rationale</a>
</h2></div></div></div>
<h4>
<a name="align.rationale.h0"></a>
<span class="phrase"><a name="align.rationale.dynamic_allocation"></a></span><a class="link" href="rationale.html#align.rationale.dynamic_allocation">Dynamic
allocation</a>
</h4>
<p>
C++11 added the ability to specify increased alignment (over-alignment) for
class types. Unfortunately, <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span> <span class="keyword">new</span></code>
allocation functions, <code class="computeroutput"><span class="keyword">new</span></code> expressions
and the Default Allocator, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code>,
do not support dynamic memory allocation of over-aligned data. This library
provides allocation functions and allocators that respect the alignment requirements
of a type and so are suitable for allocating memory for over-aligned types.
</p>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term"><code class="computeroutput"><span class="identifier">aligned_alloc</span><span class="special">(</span><span class="identifier">alignment</span><span class="special">,</span> <span class="identifier">size</span><span class="special">)</span></code></span></dt>
<dd><p>
Replaces <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span>
<span class="keyword">new</span><span class="special">(</span><span class="identifier">size</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">)</span></code>
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">aligned_free</span><span class="special">(</span><span class="identifier">pointer</span><span class="special">)</span></code></span></dt>
<dd><p>
Replaces <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span>
<span class="keyword">delete</span><span class="special">(</span><span class="identifier">pointer</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">)</span></code>
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">aligned_allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code></span></dt>
<dd><p>
Replaces <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">aligned_allocator_adaptor</span><span class="special"><</span><span class="identifier">Allocator</span><span class="special">></span></code></span></dt>
<dd><p>
Replaces use of Allocator
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">aligned_delete</span></code></span></dt>
<dd><p>
Replaces <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">default_delete</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
</p></dd>
</dl>
</div>
<h4>
<a name="align.rationale.h1"></a>
<span class="phrase"><a name="align.rationale.pointer_alignment"></a></span><a class="link" href="rationale.html#align.rationale.pointer_alignment">Pointer
alignment</a>
</h4>
<p>
C++11 provided <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">align</span></code> in the standard library to align a
pointer value. Unfortunately some C++ standard library implementations do not
support it yet (libstdc++ as far as gcc 4.8.0) and other standard library implementations
implement it incorrectly (dinkumware in msvc11.0). This library provides it
for those implementations and also for C++03 compilers where it is equally
useful.
</p>
<h4>
<a name="align.rationale.h2"></a>
<span class="phrase"><a name="align.rationale.querying_alignment"></a></span><a class="link" href="rationale.html#align.rationale.querying_alignment">Querying
alignment</a>
</h4>
<p>
C++11 provided the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">alignment_of</span></code> trait in the standard library
to query the alignment requirement of a type. Unfortunately some C++ standard
library vendors do not implement it in an entirely standard conforming manner,
such as for array types (libc++ as far as clang 3.4). Other vendor implementations
report incorrect values for certain types, such as pointer to members (msvc
14.0). This library provides it for those implementations and also for C++03
compilers where it is equally useful.
</p>
<h4>
<a name="align.rationale.h3"></a>
<span class="phrase"><a name="align.rationale.hinting_alignment"></a></span><a class="link" href="rationale.html#align.rationale.hinting_alignment">Hinting
alignment</a>
</h4>
<p>
Allocating aligned memory is sometimes not enough to ensure that optimal code
is generated. Developers use specific compiler intrinsics to notify the compiler
of a given alignment property of a memory block. This library provides a macro,
<code class="computeroutput"><span class="identifier">BOOST_ALIGN_ASSUME_ALIGNED</span></code>,
to abstract that functionality for compilers with the appropriate intrinsics.
</p>
<h4>
<a name="align.rationale.h4"></a>
<span class="phrase"><a name="align.rationale.checking_alignment"></a></span><a class="link" href="rationale.html#align.rationale.checking_alignment">Checking
alignment</a>
</h4>
<p>
This library provides a function, <code class="computeroutput"><span class="identifier">is_aligned</span></code>
to test the alignment of a pointer value. It is generally useful in assertions
to validate that memory is correctly aligned.
</p>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2014-2017 Glen
Joseph Fernandes<p>
Distributed under the Boost Software License, Version 1.0.
</p>
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