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<title>Simple Segregated Storage</title>
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<h1 align="center">Simple Segregated Storage</h1>
<h2>Introduction</h2>
<p>simple_segregated_storage.hpp provides a template class <span class=
"code">simple_segregated_storage</span> that controls access to a <em>free
list</em> of memory chunks. Please note that this is a
<strong>very</strong> simple class, with preconditions on almost all its
functions. It is intended to be the fastest and smallest possible quick
memory allocator — e.g., something to use in embedded systems. This
class delegates many difficult preconditions to the user (i.e., alignment
issues). For more general usage, see <a href="../interfaces.html">the other
pool interfaces</a>.</p>
<h2>Synopsis</h2>
<pre class="code">
template <typename SizeType = std::size_t>
class simple_segregated_storage
{
private:
simple_segregated_storage(const simple_segregated_storage &);
void operator=(const simple_segregated_storage &);
public:
typedef SizeType size_type;
simple_segregated_storage();
~simple_segregated_storage();
static void * segregate(void * block,
size_type nsz, size_type npartition_sz,
void * end = 0);
void add_block(void * block,
size_type nsz, size_type npartition_sz);
void add_ordered_block(void * block,
size_type nsz, size_type npartition_sz);
bool empty() const;
void * malloc();
void free(void * chunk);
void ordered_free(void * chunk);
void * malloc_n(size_type n, size_type partition_sz);
void free_n(void * chunks, size_type n,
size_type partition_sz);
void ordered_free_n(void * chunks, size_type n,
size_type partition_sz);
};
</pre>
<h2>Semantics</h2>
<p>An object of type <span class=
"code">simple_segregated_storage<SizeType></span> is <em>empty</em>
if its free list is empty. If it is not empty, then it is <em>ordered</em>
if its free list is ordered. A free list is ordered if repeated calls to
<span class="code">malloc()</span> will result in a constantly-increasing
sequence of values, as determined by <span class="code">std::less<void
*></span>. A member function is <em>order-preserving</em> if the free
list maintains its order orientation (that is, an ordered free list is
still ordered after the member function call).</p>
<table border align="center" summary="">
<caption>
<em>Symbol Table</em>
</caption>
<tr>
<th>Symbol</th>
<th>Meaning</th>
</tr>
<tr>
<td class="code">Store</td>
<td class="code">simple_segregated_storage<SizeType></td>
</tr>
<tr>
<td class="code">t</td>
<td>value of type <span class="code">Store</span></td>
</tr>
<tr>
<td class="code">u</td>
<td>value of type <span class="code">const Store</span></td>
</tr>
<tr>
<td class="code">block, chunk, end</td>
<td>values of type <span class="code">void *</span></td>
</tr>
<tr>
<td class="code">partition_sz, sz, n</td>
<td>values of type <span class="code">Store::size_type</span></td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Template Parameters</em>
</caption>
<tr>
<th>Parameter</th>
<th>Default</th>
<th>Requirements</th>
</tr>
<tr>
<td class="code">SizeType</td>
<td class="code">std::size_t</td>
<td>An unsigned integral type</td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Typedefs</em>
</caption>
<tr>
<th>Symbol</th>
<th>Type</th>
</tr>
<tr>
<td class="code">size_type</td>
<td class="code">SizeType</td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Constructors, Destructors, and State</em>
</caption>
<tr>
<th>Expression</th>
<th>Return Type</th>
<th>Post-Condition</th>
<th>Notes</th>
</tr>
<tr>
<td class="code">Store()</td>
<td>not used</td>
<td class="code">empty()</td>
<td>Constructs a new <span class="code">Store</span></td>
</tr>
<tr>
<td class="code">(&t)->~Store()</td>
<td>not used</td>
<td></td>
<td>Destructs the <span class="code">Store</span></td>
</tr>
<tr>
<td class="code">u.empty()</td>
<td class="code">bool</td>
<td></td>
<td>Returns <span class="code">true</span> if <span class=
"code">u</span> is empty. Order-preserving.</td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Segregation</em>
</caption>
<tr>
<th>Expression</th>
<th>Return Type</th>
<th>Pre-Condition</th>
<th>Post-Condition</th>
<th>Semantic Equivalence</th>
<th>Notes</th>
</tr>
<tr>
<td class="code">Store::segregate(block, sz, partition_sz, end)</td>
<td class="code">void *</td>
<td><span class="code">partition_sz >= sizeof(void *)</span><br>
<span class="code">partition_sz = sizeof(void *) * i</span>, for some
integer <span class="code">i</span><br>
<span class="code">sz >= partition_sz</span><br>
<span class="code">block</span> is properly aligned for an array of
objects of size <span class="code">partition_sz</span><br>
<span class="code">block</span> is properly aligned for an array of
<span class="code">void *</span></td>
<td></td>
<td></td>
<td>Interleaves a free list through the memory block specified by
<span class="code">block</span> of size <span class="code">sz</span>
bytes, partitioning it into as many <span class=
"code">partition_sz</span>-sized chunks as possible. The last chunk is
set to point to <span class="code">end</span>, and a pointer to the
first chunck is returned (this is always equal to <span class=
"code">block</span>). This interleaved free list is ordered.
O(sz).</td>
</tr>
<tr>
<td class="code">Store::segregate(block, sz, partition_sz)</td>
<td class="code">void *</td>
<td>Same as above</td>
<td></td>
<td class="code">Store::segregate(block, sz, partition_sz, 0)</td>
<td></td>
</tr>
<tr>
<td class="code">t.add_block(block, sz, partition_sz)</td>
<td class="code">void</td>
<td>Same as above</td>
<td class="code">!t.empty()</td>
<td></td>
<td>Segregates the memory block specified by <span class=
"code">block</span> of size <span class="code">sz</span> bytes into
<span class="code">partition_sz</span>-sized chunks, and adds that free
list to its own. If <span class="code">t</span> was empty before this
call, then it is ordered after this call. O(sz).</td>
</tr>
<tr>
<td class="code">t.add_ordered_block(block, sz, partition_sz)</td>
<td class="code">void</td>
<td>Same as above</td>
<td class="code">!t.empty()</td>
<td></td>
<td>Segregates the memory block specified by <span class=
"code">block</span> of size <span class="code">sz</span> bytes into
<span class="code">partition_sz</span>-sized chunks, and merges that
free list into its own. Order-preserving. O(sz).</td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Allocation and Deallocation</em>
</caption>
<tr>
<th>Expression</th>
<th>Return Type</th>
<th>Pre-Condition</th>
<th>Post-Condition</th>
<th>Semantic Equivalence</th>
<th>Notes</th>
</tr>
<tr>
<td class="code">t.malloc()</td>
<td class="code">void *</td>
<td class="code">!t.empty()</td>
<td></td>
<td></td>
<td>Takes the first available chunk from the free list and returns it.
Order-preserving. O(1).</td>
</tr>
<tr>
<td class="code">t.free(chunk)</td>
<td class="code">void</td>
<td><span class="code">chunk</span> was previously returned from a call
to <span class="code">t.malloc()</span></td>
<td class="code">!t.empty()</td>
<td></td>
<td>Places <span class="code">chunk</span> back on the free list. Note
that <span class="code">chunk</span> may not be <span class=
"code">0</span>. O(1).</td>
</tr>
<tr>
<td class="code">t.ordered_free(chunk)</td>
<td class="code">void</td>
<td>Same as above</td>
<td class="code">!t.empty()</td>
<td></td>
<td>Places <span class="code">chunk</span> back on the free list. Note
that <span class="code">chunk</span> may not be <span class=
"code">0</span>. Order-preserving. O(N) with respect to the size of the
free list.</td>
</tr>
<tr>
<td class="code">t.malloc_n(n, partition_sz)</td>
<td class="code">void *</td>
<td></td>
<td></td>
<td></td>
<td>Attempts to find a contiguous sequence of <span class=
"code">n</span> <span class="code">partition_sz</span>-sized chunks. If
found, removes them all from the free list and returns a pointer to the
first. If not found, returns <span class="code">0</span>. It is
strongly recommended (but not required) that the free list be ordered,
as this algorithm will fail to find a contiguous sequence unless it is
contiguous in the free list as well. Order-preserving. O(N) with
respect to the size of the free list.</td>
</tr>
<tr>
<td class="code">t.free_n(chunk, n, partition_sz)</td>
<td class="code">void</td>
<td><span class="code">chunk</span> was previously returned from a call
to <span class="code">t.malloc_n(n, partition_sz)</span></td>
<td class="code">!t.empty()</td>
<td class="code">t.add_block(chunk, n * partition_sz,
partition_sz)</td>
<td>Assumes that <span class="code">chunk</span> actually refers to a
block of chunks spanning <span class="code">n * partition_sz</span>
bytes; segregates and adds in that block. Note that <span class=
"code">chunk</span> may not be <span class="code">0</span>. O(n).</td>
</tr>
<tr>
<td class="code">t.ordered_free_n(chunk, n, partition_sz)</td>
<td class="code">void</td>
<td>same as above</td>
<td>same as above</td>
<td class="code">t.add_ordered_block(chunk, n * partition_sz,
partition_sz)</td>
<td>Same as above, except it merges in the free list. Order-preserving.
O(N + n) where N is the size of the free list.</td>
</tr>
</table>
<h2>Symbols</h2>
<ul>
<li>boost::simple_segregated_storage</li>
</ul>
<h2><a href=
"../implementation/simple_segregated_storage.html">Implementation
Details</a></h2>
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<p>Revised
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
<p><i>Copyright © 2000, 2001 Stephen Cleary (scleary AT jerviswebb DOT
com)</i></p>
<p><i>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
or copy at <a href=
"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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