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diff --git a/gcc-4.8.1/libstdc++-v3/doc/html/manual/unordered_associative.html b/gcc-4.8.1/libstdc++-v3/doc/html/manual/unordered_associative.html deleted file mode 100644 index 578108901..000000000 --- a/gcc-4.8.1/libstdc++-v3/doc/html/manual/unordered_associative.html +++ /dev/null @@ -1,64 +0,0 @@ -<?xml version="1.0" encoding="UTF-8" standalone="no"?> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Unordered Associative</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.77.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="containers.html" title="Chapter 9. Containers" /><link rel="prev" href="associative.html" title="Associative" /><link rel="next" href="containers_and_c.html" title="Interacting with C" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Unordered Associative</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="associative.html">Prev</a> </td><th width="60%" align="center">Chapter 9. - Containers - -</th><td width="20%" align="right"> <a accesskey="n" href="containers_and_c.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.containers.unordered"></a>Unordered Associative</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="containers.unordered.hash"></a>Hash Code</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="containers.unordered.cache"></a>Hash Code Caching Policy</h4></div></div></div><p> - The unordered containers in libstdc++ may cache the hash code for each - element alongside the element itself. In some cases not recalculating - the hash code every time it's needed can improve performance, but the - additional memory overhead can also reduce performance, so whether an - unordered associative container caches the hash code or not depends on - a number of factors. The caching policy for GCC 4.8 is described below. - </p><p> - The C++ standard requires that <code class="code">erase</code> and <code class="code">swap</code> - operations must not throw exceptions. Those operations might need an - element's hash code, but cannot use the hash function if it could - throw. - This means the hash codes will be cached unless the hash function - has a non-throwing exception specification such as <code class="code">noexcept</code> - or <code class="code">throw()</code>. - </p><p> - Secondly, libstdc++ also needs the hash code in the implementation of - <code class="code">local_iterator</code> and <code class="code">const_local_iterator</code> in - order to know when the iterator has reached the end of the bucket. - This means that the local iterator types will embed a copy of the hash - function when possible. - Because the local iterator types must be DefaultConstructible and - CopyAssignable, if the hash function type does not model those concepts - then it cannot be embedded and so the hash code must be cached. - Note that a hash function might not be safe to use when - default-constructed (e.g if it a function pointer) so a hash - function that is contained in a local iterator won't be used until - the iterator is valid, so the hash function has been copied from a - correctly-initialized object. - </p><p> - If the hash function is non-throwing, DefaultConstructible and - CopyAssignable then libstdc++ doesn't need to cache the hash code for - correctness, but might still do so for performance if computing a - hash code is an expensive operation, as it may be for arbitrarily - long strings. - As an extension libstdc++ provides a trait type to describe whether - a hash function is fast. By default hash functions are assumed to be - fast unless the trait is specialized for the hash function and the - trait's value is false, in which case the hash code will always be - cached. - The trait can be specialized for user-defined hash functions like so: - </p><pre class="programlisting"> - #include <unordered_set> - - struct hasher - { - std::size_t operator()(int val) const noexcept - { - // Some very slow computation of a hash code from an int ! - ... - } - } - - namespace std - { - template<> - struct __is_fast_hash<hasher> : std::false_type - { }; - } - </pre></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="associative.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="containers.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="containers_and_c.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Associative </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Interacting with C</td></tr></table></div></body></html>
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