mirror of git://gcc.gnu.org/git/gcc.git
147 lines
6.1 KiB
XML
147 lines
6.1 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook" version="5.0"
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xml:id="std.numerics" xreflabel="Numerics">
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<?dbhtml filename="numerics.html"?>
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<info><title>
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Numerics
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<indexterm><primary>Numerics</primary></indexterm>
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</title>
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<keywordset>
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<keyword>ISO C++</keyword>
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<keyword>library</keyword>
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</keywordset>
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</info>
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<!-- Sect1 01 : Complex -->
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<section xml:id="std.numerics.complex" xreflabel="complex"><info><title>Complex</title></info>
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<?dbhtml filename="complex.html"?>
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<para>
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</para>
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<section xml:id="numerics.complex.processing" xreflabel="complex Processing"><info><title>complex Processing</title></info>
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<para>
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</para>
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<para>Using <code>complex<></code> becomes even more comple- er, sorry,
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<emphasis>complicated</emphasis>, with the not-quite-gratuitously-incompatible
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addition of complex types to the C language. David Tribble has
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compiled a list of C++98 and C99 conflict points; his description of
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C's new type versus those of C++ and how to get them playing together
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nicely is
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<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://david.tribble.com/text/cdiffs.htm#C99-complex">here</link>.
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</para>
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<para><code>complex<></code> is intended to be instantiated with a
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floating-point type. As long as you meet that and some other basic
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requirements, then the resulting instantiation has all of the usual
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math operators defined, as well as definitions of <code>op<<</code>
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and <code>op>></code> that work with iostreams: <code>op<<</code>
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prints <code>(u,v)</code> and <code>op>></code> can read <code>u</code>,
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<code>(u)</code>, and <code>(u,v)</code>.
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</para>
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<para>As an extension to C++11 and for increased compatibility with C,
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<code><complex.h></code> includes both <code><complex></code>
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and the C99 <code><complex.h></code> (if the C library provides
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it).
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</para>
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</section>
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</section>
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<!-- Sect1 02 : Generalized Operations -->
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<section xml:id="std.numerics.generalized_ops" xreflabel="Generalized Ops"><info><title>Generalized Operations</title></info>
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<?dbhtml filename="generalized_numeric_operations.html"?>
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<para>
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</para>
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<para>There are four generalized functions in the <numeric> header
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that follow the same conventions as those in <algorithm>. Each
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of them is overloaded: one signature for common default operations,
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and a second for fully general operations. Their names are
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self-explanatory to anyone who works with numerics on a regular basis:
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</para>
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<itemizedlist>
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<listitem><para><code>accumulate</code></para></listitem>
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<listitem><para><code>inner_product</code></para></listitem>
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<listitem><para><code>partial_sum</code></para></listitem>
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<listitem><para><code>adjacent_difference</code></para></listitem>
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</itemizedlist>
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<para>Here is a simple example of the two forms of <code>accumulate</code>.
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</para>
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<programlisting>
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int ar[50];
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int someval = somefunction();
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// ...initialize members of ar to something...
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int sum = std::accumulate(ar,ar+50,0);
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int sum_stuff = std::accumulate(ar,ar+50,someval);
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int product = std::accumulate(ar,ar+50,1,std::multiplies<int>());
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</programlisting>
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<para>The first call adds all the members of the array, using zero as an
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initial value for <code>sum</code>. The second does the same, but uses
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<code>someval</code> as the starting value (thus, <code>sum_stuff == sum +
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someval</code>). The final call uses the second of the two signatures,
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and multiplies all the members of the array; here we must obviously
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use 1 as a starting value instead of 0.
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</para>
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<para>The other three functions have similar dual-signature forms.
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</para>
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</section>
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<!-- Sect1 03 : Interacting with C -->
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<section xml:id="std.numerics.c" xreflabel="Interacting with C"><info><title>Interacting with C</title></info>
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<?dbhtml filename="numerics_and_c.html"?>
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<section xml:id="numerics.c.array" xreflabel="Numerics vs. Arrays"><info><title>Numerics vs. Arrays</title></info>
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<para>One of the major reasons why FORTRAN can chew through numbers so well
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is that it is defined to be free of pointer aliasing, an assumption
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that C89 is not allowed to make, and neither is C++98. C99 adds a new
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keyword, <code>restrict</code>, to apply to individual pointers. The
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C++ solution is contained in the library rather than the language
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(although many vendors can be expected to add this to their compilers
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as an extension).
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</para>
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<para>That library solution is a set of two classes, five template classes,
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and "a whole bunch" of functions. The classes are required
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to be free of pointer aliasing, so compilers can optimize the
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daylights out of them the same way that they have been for FORTRAN.
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They are collectively called <code>valarray</code>, although strictly
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speaking this is only one of the five template classes, and they are
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designed to be familiar to people who have worked with the BLAS
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libraries before.
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</para>
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</section>
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<section xml:id="numerics.c.c99" xreflabel="C99"><info><title>C99</title></info>
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<para>In addition to the other topics on this page, we'll note here some
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of the C99 features that appear in libstdc++.
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</para>
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<para>The C99 features depend on the <code>--enable-c99</code> configure flag.
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This flag is already on by default, but it can be disabled by the
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user. Also, the configuration machinery will disable it if the
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necessary support for C99 (e.g., header files) cannot be found.
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</para>
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<para>As of GCC 3.0, C99 support includes classification functions
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such as <code>isnormal</code>, <code>isgreater</code>,
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<code>isnan</code>, etc.
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The functions used for 'long long' support such as <code>strtoll</code>
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are supported, as is the <code>lldiv_t</code> typedef. Also supported
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are the wide character functions using 'long long', like
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<code>wcstoll</code>.
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</para>
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</section>
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</section>
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</chapter>
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