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| <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 23. Interacting with C</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="numerics.html" title="Part X. Numerics" /><link rel="prev" href="generalized_numeric_operations.html" title="Chapter 22. Generalized Operations" /><link rel="next" href="bk01pt10ch23s02.html" title="C99" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 23. Interacting with C</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="generalized_numeric_operations.html">Prev</a> </td><th width="60%" align="center">Part X. |
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| </th><td width="20%" align="right"> <a accesskey="n" href="bk01pt10ch23s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="manual.numerics.c"></a>Chapter 23. Interacting with C</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="numerics_and_c.html#numerics.c.array">Numerics vs. Arrays</a></span></dt><dt><span class="sect1"><a href="bk01pt10ch23s02.html">C99</a></span></dt></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="numerics.c.array"></a>Numerics vs. Arrays</h2></div></div></div><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 class="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 class="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. |
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