| <?xml version="1.0" encoding="ISO-8859-1"?> |
| <!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" xml:lang="en" lang="en"> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> |
| <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" /> |
| <meta name="KEYWORDS" content="HOWTO, libstdc++, GCC, g++, libg++, STL" /> |
| <meta name="DESCRIPTION" content="HOWTO for the libstdc++ chapter 26." /> |
| <meta name="GENERATOR" content="vi and eight fingers" /> |
| <title>libstdc++-v3 HOWTO: Chapter 26: Numerics</title> |
| <link rel="StyleSheet" href="../lib3styles.css" type="text/css" /> |
| <link rel="Start" href="../documentation.html" type="text/html" |
| title="GNU C++ Standard Library" /> |
| <link rel="Prev" href="../25_algorithms/howto.html" type="text/html" |
| title="Algorithms" /> |
| <link rel="Next" href="../27_io/howto.html" type="text/html" |
| title="Input/Output" /> |
| <link rel="Copyright" href="../17_intro/license.html" type="text/html" /> |
| <link rel="Help" href="../faq/index.html" type="text/html" title="F.A.Q." /> |
| </head> |
| <body> |
| |
| <h1 class="centered"><a name="top">Chapter 26: Numerics</a></h1> |
| |
| <p>Chapter 26 deals with building block abstractions to aid in |
| numerical computing: |
| </p> |
| <ul> |
| <li>Template data structures such as <code>valarray<></code> |
| and <code>complex<></code>. |
| </li> |
| <li>Template numerical functions such as <code>accumulate</code>, |
| <code>inner_product</code>, <code>partial_sum</code>, and |
| <code>adjacent_difference</code>. |
| </li> |
| </ul> |
| <p>All of the Standard C math functions are of course included in C++, |
| and overloaded versions for <code>long</code>, <code>float</code>, and |
| <code>long double</code> have been added for all of them. |
| </p> |
| |
| <!-- ####################################################### --> |
| <hr /> |
| <h1>Contents</h1> |
| <ul> |
| <li><a href="#1">Complex Number Processing</a></li> |
| <li><a href="#2">Array Processing</a></li> |
| <li><a href="#3">Numerical Functions</a></li> |
| <li><a href="#4">C99</a></li> |
| </ul> |
| |
| <hr /> |
| |
| <!-- ####################################################### --> |
| |
| <h2><a name="1">Complex Number Processing</a></h2> |
| <p>Using <code>complex<></code> becomes even more comple- er, sorry, |
| <em>complicated</em>, with the not-quite-gratuitously-incompatible |
| addition of complex types to the C language. David Tribble has |
| compiled a list of C++98 and C99 conflict points; his description of |
| C's new type versus those of C++ and how to get them playing together |
| nicely is |
| <a href="http://david.tribble.com/text/cdiffs.htm#C99-complex">here</a>. |
| </p> |
| <p><code>complex<></code> is intended to be instantiated with a |
| floating-point type. As long as you meet that and some other basic |
| requirements, then the resulting instantiation has all of the usual |
| math operators defined, as well as definitions of <code>op<<</code> |
| and <code>op>></code> that work with iostreams: <code>op<<</code> |
| prints <code>(u,v)</code> and <code>op>></code> can read <code>u</code>, |
| <code>(u)</code>, and <code>(u,v)</code>. |
| </p> |
| <p>Return <a href="#top">to top of page</a> or |
| <a href="../faq/index.html">to the FAQ</a>. |
| </p> |
| |
| <hr /> |
| <h2><a name="2">Array Processing</a></h2> |
| <p>One of the major reasons why FORTRAN can chew through numbers so well |
| is that it is defined to be free of pointer aliasing, an assumption |
| that C89 is not allowed to make, and neither is C++98. C99 adds a new |
| keyword, <code>restrict</code>, to apply to individual pointers. The |
| C++ solution is contained in the library rather than the language |
| (although many vendors can be expected to add this to their compilers |
| as an extension). |
| </p> |
| <p>That library solution is a set of two classes, five template classes, |
| and "a whole bunch" of functions. The classes are required |
| to be free of pointer aliasing, so compilers can optimize the |
| daylights out of them the same way that they have been for FORTRAN. |
| They are collectively called <code>valarray</code>, although strictly |
| speaking this is only one of the five template classes, and they are |
| designed to be familiar to people who have worked with the BLAS |
| libraries before. |
| </p> |
| <p>Some more stuff should go here once somebody has time to write it. |
| </p> |
| <p>Return <a href="#top">to top of page</a> or |
| <a href="../faq/index.html">to the FAQ</a>. |
| </p> |
| |
| <hr /> |
| <h2><a name="3">Numerical Functions</a></h2> |
| <p>There are four generalized functions in the <numeric> header |
| that follow the same conventions as those in <algorithm>. Each |
| of them is overloaded: one signature for common default operations, |
| and a second for fully general operations. Their names are |
| self-explanatory to anyone who works with numerics on a regular basis: |
| </p> |
| <ul> |
| <li><code>accumulate</code></li> |
| <li><code>inner_product</code></li> |
| <li><code>partial_sum</code></li> |
| <li><code>adjacent_difference</code></li> |
| </ul> |
| <p>Here is a simple example of the two forms of <code>accumulate</code>. |
| </p> |
| <pre> |
| int ar[50]; |
| int someval = somefunction(); |
| |
| // ...initialize members of ar to something... |
| |
| int sum = std::accumulate(ar,ar+50,0); |
| int sum_stuff = std::accumulate(ar,ar+50,someval); |
| int product = std::accumulate(ar,ar+50,1,std::multiplies<int>()); |
| </pre> |
| <p>The first call adds all the members of the array, using zero as an |
| initial value for <code>sum</code>. The second does the same, but uses |
| <code>someval</code> as the starting value (thus, <code>sum_stuff == sum + |
| someval</code>). The final call uses the second of the two signatures, |
| and multiplies all the members of the array; here we must obviously |
| use 1 as a starting value instead of 0. |
| </p> |
| <p>The other three functions have similar dual-signature forms. |
| </p> |
| <p>Return <a href="#top">to top of page</a> or |
| <a href="../faq/index.html">to the FAQ</a>. |
| </p> |
| |
| <hr /> |
| <h2><a name="4">C99</a></h2> |
| <p>In addition to the other topics on this page, we'll note here some |
| of the C99 features that appear in libstdc++-v3. |
| </p> |
| <p>The C99 features depend on the <code>--enable-c99</code> configure flag. |
| This flag is already on by default, but it can be disabled by the |
| user. Also, the configuration machinery will disable it if the |
| necessary support for C99 (e.g., header files) cannot be found. |
| </p> |
| <p>As of GCC 3.0, C99 support includes classification functions |
| such as <code>isnormal</code>, <code>isgreater</code>, |
| <code>isnan</code>, etc. |
| The functions used for 'long long' support such as <code>strtoll</code> |
| are supported, as is the <code>lldiv_t</code> typedef. Also supported |
| are the wide character functions using 'long long', like |
| <code>wcstoll</code>. |
| </p> |
| <p>Return <a href="#top">to top of page</a> or |
| <a href="../faq/index.html">to the FAQ</a>. |
| </p> |
| |
| |
| |
| <!-- ####################################################### --> |
| |
| <hr /> |
| <p class="fineprint"><em> |
| See <a href="../17_intro/license.html">license.html</a> for copying conditions. |
| Comments and suggestions are welcome, and may be sent to |
| <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>. |
| </em></p> |
| |
| |
| </body> |
| </html> |
