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585 lines
26 KiB
HTML
<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns="http://www.w3.org/TR/REC-html40">
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<head>
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<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
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<meta name="ProgId" content="FrontPage.Editor.Document">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>Boost Endian Library</title>
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<style type="text/css">
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ins {background-color:#CCFFCC}
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del {background-color:#FFCACA}
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body { font-family: sans-serif; width:8.0in; }
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pre { background-color:#D7EEFF }
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<body>
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<table border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" width="100%">
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<tr>
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<td>
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<a href="../../../index.html">
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<img src="../../../boost.png" alt="boost.png (6897 bytes)" align="middle" border="0" width="277" height="86"></a></td>
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<td align="middle">
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<font size="7">Endian Library</font></td>
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</tr>
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</table>
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<table border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF" width="100%">
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<tr>
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<td><b><a href="../../../index.htm">Boost Home</a>
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<a href="index.html">Endian Home</a>
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<a href="conversion.html">Conversion Functions</a>
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<a href="types.html">Endian Types</a></b></td>
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</tr>
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</table>
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<p></p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" align="right">
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<tr>
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<td width="100%" bgcolor="#D7EEFF" align="center">
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<i><b>Contents</b></i></td>
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</tr>
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<tr>
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<td width="100%" bgcolor="#E8F5FF">
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<a href="#Abstract">Abstract</a><br>
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<a href="#Introduction-to-endianness">Introduction to endianness</a><br>
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<a href="#Introduction">Introduction to the Boost.Endian library</a><br>
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<a href="#Choosing">Choosing approaches</a><br>
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<a href="#Intrinsic">Intrinsic built-in support</a><br>
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<a href="#Performance">Performance</a><br>
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<a href="#Timings">Timings</a><br>
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<a href="#Conclusions">Conclusions</a><br>
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<a href="#FAQ">FAQ</a><br>
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<a href="#Release-history">Release history</a><br>
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<a href="#Acknowledgements">Acknowledgements</a></td>
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</tr>
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<tr>
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<td width="100%" bgcolor="#D7EEFF" align="center">
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<b><i>Headers</i></b></td>
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</tr>
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<tr>
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<td width="100%" bgcolor="#E8F5FF">
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<a href="../include/boost/endian/conversion.hpp"><boost/endian/conversion.hpp></a><br>
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<a href="../include/boost/endian/types.hpp"><boost/endian/types.hpp></a></td>
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</tr>
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</table>
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<table border="1" cellpadding="0" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111">
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<tr>
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<td>Heads up: As development has continues, there have been breaking
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changes. Most recently, the <a href="types.html">endian types</a> were
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renamed.</td>
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</tr>
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</table>
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<h2><a name="Abstract">Abstract</a></h2>
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<p>Boost.Endian provides facilities to manipulate the endianness of integers,
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floating point, and user defined data.</p>
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<ul>
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<li>The primary use case is binary I/O for portable data exchange with
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other systems, via either file or network transmission.<br>
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</li>
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<li>A secondary use case is minimizing storage size via sizes and/or
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alignments not supported by the built-in types.<br>
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</li>
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<li>Two distinct approaches to dealing with endianness are provided. Each approach has a
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long history of successful use, and each approach has use cases where it is
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superior to the other approach.</li>
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</ul>
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<h2><a name="Introduction-to-endianness">Introduction to endianness</a></h2>
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<p>Consider the following code:</p>
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<blockquote>
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<pre>int16_t i = 0x0102;
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FILE * file = fopen("test.bin", "wb"); // binary file!
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fwrite(&i, sizeof(int16_t), 1, file);
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fclose(file);</pre>
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</blockquote>
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<p>On OS X, Linux, or Windows systems with an Intel CPU, a hex dump
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of the "test.bin" output file produces:</p>
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<blockquote>
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<p><code>0201</code></p>
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</blockquote>
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<p>On OS X systems with a PowerPC CPU, or Solaris systems with a SPARC CPU, a hex dump of the "test.bin"
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output file produces:</p>
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<blockquote>
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<p><code>0102</code></p>
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</blockquote>
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<p>What's happening here is that Intel CPUs order the bytes of an integer with
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the least-significant byte first, while SPARC CPUs place the most-significant
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byte first. Some CPUs, such as the PowerPC, allow the operating system to
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choose which ordering applies.</p>
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<p><a name="definition"></a>Most-significant-byte-first ordering is traditionally called "big endian"
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ordering and the least-significant-byte-first is traditionally called
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"little-endian" ordering. The names are derived from
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<a href="http://en.wikipedia.org/wiki/Jonathan_Swift" title="Jonathan Swift">
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Jonathan Swift</a>'s satirical novel <i>
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<a href="http://en.wikipedia.org/wiki/Gulliver's_Travels" title="Gulliver's Travels">
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Gulliver’s Travels</a></i>, where rival kingdoms opened their soft-boiled eggs
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at different ends.</p>
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<p>See the Wikipedia's
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<a href="http://en.wikipedia.org/wiki/Endianness">Endianness</a> article for an
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extensive discussion of endianness.</p>
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<p>Most programmers can ignore endianness, except perhaps for reading a core
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dump on little-endian systems. Programmers have to deal with endianness in their
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code when exchanging binary integers and binary floating point
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values between computer systems with differing endianness, whether by physical file transfer or over a network,
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. </p>
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<h2><a name="Introduction">Introduction</a> to the Boost.Endian library</h2>
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<p>The Boost.Endian library provides two different approaches to dealing with
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integer endianness. Both approaches support integers, floating point types
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except <code>long double</code>, and user defined types (UDTs).</p>
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<p>Each approach has a long history of successful use, and each approach has use
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cases where it is superior to the other approach.</p>
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<blockquote>
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<p><b><a href="types.html">Endian types</a> -</b> The application uses the provided endian types
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which mimic the
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built-in integer types. For example, <code>big_int32_t</code> or <code>little_float64_t</code>.
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Integer types with lengths of 1 through 8 bytes are supported, rather than just
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2, 4, and 8 byte integers. The types may be aligned or unaligned.</p>
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<p><b><a href="conversion.html">Endian conversion functions</a> -</b> The
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application uses the built-in integer and floating point types, and calls the
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provided conversion functions to convert byte ordering as needed. Both mutating
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and non-mutating conversions are supplied, and each comes in unconditional and
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conditional variants.</p>
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</blockquote>
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<p>Boost Endian is a header-only library.</p>
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<h2><a name="Choosing">Choosing</a> between endian types and endian
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conversion functions</h2>
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<p>Which approach is better for dealing with endianness depends on
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application needs.</p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111">
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<tr>
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<th colspan="2">Needs that favor one approach over the other</th>
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</tr>
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<tr>
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<th width="50%"><b><a href="types.html">Endian types</a> are better with
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these needs</b></th>
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<th><b><a href="conversion.html">Endian conversion functions</a> are better
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with these needs</b></th>
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</tr>
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<tr>
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<td valign="top">
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<ul>
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<li>A need to simplify program logic and eliminate logic
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errors. Since the endian types mimic the built-in types, there is no need to reason about the current endianness of variables
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and that can simplify program logic and eliminate logic errors.<br>
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</li>
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<li>A need to use unusual integer sizes (i.e. 3, 5,
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6, or 7 bytes) to reduce internal and external space usage and
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save I/O time.<br>
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</li>
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<li>A need to use unaligned variables. Endian types can eliminate padding bytes in
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structures, reducing internal and external space usage and saving I/O
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time. They can deals with structures defined like this:</li>
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</ul>
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<blockquote>
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<p><code>struct S {<br>
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uint16_t a;<br>
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uint32_t b;<br>
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} __attribute__ ((packed));</code></p>
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</blockquote>
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</td>
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<td valign="top">
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<ul>
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<li>A need to leverage knowledge of developers who have been using C byte
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swapping
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functions for years.<br>
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</li>
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<li>A need to save CPU time when a variable is used many times
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relative to its I/O.<br>
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</li>
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<li>A need to pass structures to third-party libraries expecting a
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specific structure format.<br>
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</li>
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</ul>
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</td>
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</tr>
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</table>
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<h2><a name="Intrinsic">Intrinsic</a> built-in support</h2>
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<p>Recent compilers, including GCC, Clang, and Microsoft, supply intrinsic
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built-in support for byte swapping. Such support is automatically detected and
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used since it may in smaller and faster generated code, particularly for release
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builds.</p>
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<p dir="ltr">Defining <code>BOOST_ENDIAN_NO_INTRINSICS</code> will suppress use
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of the intrinsics. Please try defining it if you get compiler errors, such as
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header byteswap.h not being found.</p>
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<p dir="ltr">The macro <code>BOOST_ENDIAN_INTRINSIC_MSG</code> is defined as
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either <code>"no byte swap intrinsics"</code> or a string describing the
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particular set of intrinsics being used.</p>
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<h2><a name="Performance">Performance</a></h2>
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<p>Consider this problem:</p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111">
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<tr>
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<td colspan="2">
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<p align="center"><i><b><a name="Example-1">Example 1</a></b></i></td>
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</tr>
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<tr>
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<td colspan="2"><b><i>Add 100 to a big endian value in a file, then write the
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result to a file</i> </b> </td>
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</tr>
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<tr>
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<td><i><b>Endian type approach</b></i></td>
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<td><i><b>Endian conversion approach</b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>big_int32_t x;
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... read into x from a file ...
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x += 100;
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... write x to a file ...
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</pre>
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</td>
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<td>
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<pre>
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int32_t x;
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... read into x from a file ...
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big_endian(x);
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x += 100;
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big_endian(x);
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... write x to a file ...
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</pre>
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</td>
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</tr>
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</table>
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<p><b>There will be no performance difference between the two approaches,
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regardless of the native endianness of the machine.</b> Optimizing compilers will likely
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generate exactly the same code for both. That conclusion was confirmed by
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studying the generated assembly code for GCC and Visual C++.</p>
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<p>Now consider a slightly different problem: </p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111">
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<tr>
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<td colspan="2">
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<p align="center"><b><i><a name="Example-2">Example 2</a></i></b></td>
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</tr>
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<tr>
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<td colspan="2"><i><b>Add a million values to a big endian value in a file, then write the
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result to a file </b></i> </td>
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</tr>
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<tr>
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<td><i><b>Endian type approach</b></i></td>
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<td><i><b>Endian conversion approach</b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>big_int32_t x;
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... read into x from a file ...
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for (int32_t i = 0; i < 1000000; ++i)
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x += i;
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... write x to a file ...
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</pre>
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</td>
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<td>
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<pre>int32_t x;
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... read into x from a file ...
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big_endian(x);
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for (int32_t i = 0; i < 1000000; ++i)
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x += i;
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big_endian(x);
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... write x to a file ...
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</pre>
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</td>
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</tr>
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</table>
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<p>With the Endian type approach, an implicit conversion from and then back to
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big endian is done inside the loop. With the Endian conversion function
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approach, the conversions are explicit, so only need to be done once, before and
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after the loop.</p>
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<h3><a name="Timings">Timings</a> for Example 2 (conversion functions hoisted
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out of loop)</h3>
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<p>These tests were run against release builds on a circa 2012 4-core little endian X64 Intel Core i5-3570K
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CPU @ 3.40GHz under Windows 7.</p>
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<p><b>Caveat emptor: The Windows CPU timer has very high granularity. Repeated
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runs of the same tests often yield considerably different results.</b></p>
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<p>See <a href="../test/loop_time_test.cpp">loop_time_test.cpp</a> and
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<a href="../build/Jamfile.v2">Jamfile.v2</a> for the actual code and build
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setup.
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(For GCC 4.7, there are no 16-bit intrinsics, so they are emulated by using
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32-bit intrinsics.)</p>
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<table border="1" cellpadding="5" cellspacing="0"style="border-collapse: collapse" bordercolor="#111111">
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<tr><td colspan="6" align="center"><b>GNU C++ version 4.7.0</b></td></tr>
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<tr><td colspan="6" align="center"><b> Iterations: 1000000000, Intrinsics: __builtin_bswap16, etc.</b></td></tr>
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<tr><td><b>Test Case</b></td>
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<td align="center"><b>Endian<br>type</b></td>
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<td align="center"><b>Endian<br>conversion<br>function</b></td>
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</tr>
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<tr><td>16-bit aligned big endian</td><td align="right">1.37 s</td><td align="right">0.81 s</td></tr>
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<tr><td>16-bit aligned little endian</td><td align="right">0.83 s</td><td align="right">0.81 s</td></tr>
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<tr><td>16-bit unaligned big endian</td><td align="right">1.09 s</td><td align="right">0.83 s</td></tr>
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<tr><td>16-bit unaligned little endian</td><td align="right">1.09 s</td><td align="right">0.81 s</td></tr>
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<tr><td>32-bit aligned big endian</td><td align="right">0.98 s</td><td align="right">0.27 s</td></tr>
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<tr><td>32-bit aligned little endian</td><td align="right">0.28 s</td><td align="right">0.27 s</td></tr>
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<tr><td>32-bit unaligned big endian</td><td align="right">3.82 s</td><td align="right">0.27 s</td></tr>
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<tr><td>32-bit unaligned little endian</td><td align="right">3.82 s</td><td align="right">0.27 s</td></tr>
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<tr><td>64-bit aligned big endian</td><td align="right">1.65 s</td><td align="right">0.41 s</td></tr>
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<tr><td>64-bit aligned little endian</td><td align="right">0.41 s</td><td align="right">0.41 s</td></tr>
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<tr><td>64-bit unaligned big endian</td><td align="right">17.53 s</td><td align="right">0.41 s</td></tr>
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<tr><td>64-bit unaligned little endian</td><td align="right">17.52 s</td><td align="right">0.41 s</td></tr>
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<tr><td colspan="6" align="center"><b> Iterations: 1000000000, Intrinsics: no byte swap intrinsics</b></td></tr>
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<tr><td><b>Test Case</b></td>
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<td align="center"><b>Endian<br>type</b></td>
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<td align="center"><b>Endian<br>conversion<br>function</b></td>
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</tr>
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<tr><td>16-bit aligned big endian</td><td align="right">1.95 s</td><td align="right">0.81 s</td></tr>
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<tr><td>16-bit aligned little endian</td><td align="right">0.83 s</td><td align="right">0.81 s</td></tr>
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<tr><td>16-bit unaligned big endian</td><td align="right">1.19 s</td><td align="right">0.81 s</td></tr>
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<tr><td>16-bit unaligned little endian</td><td align="right">1.20 s</td><td align="right">0.81 s</td></tr>
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<tr><td>32-bit aligned big endian</td><td align="right">0.97 s</td><td align="right">0.28 s</td></tr>
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<tr><td>32-bit aligned little endian</td><td align="right">0.27 s</td><td align="right">0.28 s</td></tr>
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<tr><td>32-bit unaligned big endian</td><td align="right">4.10 s</td><td align="right">0.27 s</td></tr>
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<tr><td>32-bit unaligned little endian</td><td align="right">4.10 s</td><td align="right">0.27 s</td></tr>
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<tr><td>64-bit aligned big endian</td><td align="right">1.64 s</td><td align="right">0.42 s</td></tr>
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<tr><td>64-bit aligned little endian</td><td align="right">0.41 s</td><td align="right">0.41 s</td></tr>
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<tr><td>64-bit unaligned big endian</td><td align="right">17.52 s</td><td align="right">0.42 s</td></tr>
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<tr><td>64-bit unaligned little endian</td><td align="right">17.52 s</td><td align="right">0.41 s</td></tr>
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</table>
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<p></p>
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<table border="1" cellpadding="5" cellspacing="0"style="border-collapse: collapse" bordercolor="#111111">
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<tr><td colspan="6" align="center"><b>Microsoft Visual C++ version 11.0</b></td></tr>
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<tr><td colspan="6" align="center"><b> Iterations: 1000000000, Intrinsics: cstdlib _byteswap_ushort, etc.</b></td></tr>
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<tr><td><b>Test Case</b></td>
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<td align="center"><b>Endian<br>type</b></td>
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<td align="center"><b>Endian<br>conversion<br>function</b></td>
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</tr>
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<tr><td>16-bit aligned big endian</td><td align="right">0.83 s</td><td align="right">0.51 s</td></tr>
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<tr><td>16-bit aligned little endian</td><td align="right">0.51 s</td><td align="right">0.50 s</td></tr>
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<tr><td>16-bit unaligned big endian</td><td align="right">1.37 s</td><td align="right">0.51 s</td></tr>
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<tr><td>16-bit unaligned little endian</td><td align="right">1.37 s</td><td align="right">0.50 s</td></tr>
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<tr><td>32-bit aligned big endian</td><td align="right" bgcolor="#CCFFCC">0.81 s</td><td align="right">0.50 s</td></tr>
|
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<tr><td>32-bit aligned little endian</td><td align="right">0.51 s</td><td align="right">0.51 s</td></tr>
|
||
<tr><td>32-bit unaligned big endian</td><td align="right">2.98 s</td><td align="right">0.53 s</td></tr>
|
||
<tr><td>32-bit unaligned little endian</td><td align="right">3.00 s</td><td align="right">0.51 s</td></tr>
|
||
<tr><td>64-bit aligned big endian</td><td align="right" bgcolor="#CCFFCC">1.33 s</td><td align="right">0.33 s</td></tr>
|
||
<tr><td>64-bit aligned little endian</td><td align="right">0.34 s</td><td align="right">0.27 s</td></tr>
|
||
<tr><td>64-bit unaligned big endian</td><td align="right">7.05 s</td><td align="right">0.33 s</td></tr>
|
||
<tr><td>64-bit unaligned little endian</td><td align="right">7.11 s</td><td align="right">0.31 s</td></tr>
|
||
|
||
<tr><td colspan="6" align="center"><b> Iterations: 1000000000, Intrinsics: no byte swap intrinsics</b></td></tr>
|
||
<tr><td><b>Test Case</b></td>
|
||
<td align="center"><b>Endian<br>type</b></td>
|
||
<td align="center"><b>Endian<br>conversion<br>function</b></td>
|
||
</tr>
|
||
<tr><td>16-bit aligned big endian</td><td align="right">0.83 s</td><td align="right">0.51 s</td></tr>
|
||
<tr><td>16-bit aligned little endian</td><td align="right">0.51 s</td><td align="right">0.51 s</td></tr>
|
||
<tr><td>16-bit unaligned big endian</td><td align="right">1.36 s</td><td align="right">0.51 s</td></tr>
|
||
<tr><td>16-bit unaligned little endian</td><td align="right">1.37 s</td><td align="right">0.51 s</td></tr>
|
||
<tr><td>32-bit aligned big endian</td><td align="right" bgcolor="#FFCACA">3.42 s</td><td align="right">0.50 s</td></tr>
|
||
<tr><td>32-bit aligned little endian</td><td align="right">0.51 s</td><td align="right">0.51 s</td></tr>
|
||
<tr><td>32-bit unaligned big endian</td><td align="right">2.93 s</td><td align="right">0.50 s</td></tr>
|
||
<tr><td>32-bit unaligned little endian</td><td align="right">2.95 s</td><td align="right">0.50 s</td></tr>
|
||
<tr><td>64-bit aligned big endian</td><td align="right" bgcolor="#FFCACA">5.99 s</td><td align="right">0.33 s</td></tr>
|
||
<tr><td>64-bit aligned little endian</td><td align="right">0.33 s</td><td align="right">0.33 s</td></tr>
|
||
<tr><td>64-bit unaligned big endian</td><td align="right">7.02 s</td><td align="right">0.27 s</td></tr>
|
||
<tr><td>64-bit unaligned little endian</td><td align="right">7.02 s</td><td align="right">0.27 s</td></tr>
|
||
|
||
</table>
|
||
|
||
|
||
<h3><a name="Conclusions">Conclusions</a></h3>
|
||
|
||
<p>When program logic dictates many more conversions for the Endian integer
|
||
approach than the Endian conversion function approach (<a href="#Example-2">example
|
||
2</a>):</p>
|
||
|
||
<blockquote>
|
||
|
||
<p><b>There may be a considerable performance difference. </b>If machine endianness differs from the
|
||
desired endianness, the Endian type approach must do the byte reversal many
|
||
times while the Endian conversion approach only does the reversal once. But if
|
||
the endianness is the same, there is no conversion with either approach and no
|
||
conversion code is generated for typical release builds.</p>
|
||
|
||
<p><b>Whether or not compiler byte swap intrinsics are explicitly available has little
|
||
impact as tested.</b> Byte swap intrinsics are not available on some older
|
||
compilers and on some machine architectures, such as pre-486 X86 CPUs.</p>
|
||
|
||
<p><b>Unaligned types are much slower that aligned types, regardless of
|
||
endianness considerations.</b> Instead of single instruction register loads and
|
||
stores, multiple instructions are required.</p>
|
||
|
||
</blockquote>
|
||
|
||
|
||
<h2>Overall <a name="FAQ">FAQ</a></h2>
|
||
|
||
<p><b>Is the implementation header only?</b></p>
|
||
|
||
<blockquote>
|
||
|
||
<p>Yes.</p>
|
||
|
||
</blockquote>
|
||
|
||
<p><b>Does the implementation use compiler intrinsic built-in byte swapping?</b></p>
|
||
|
||
<blockquote>
|
||
|
||
<p>Yes, if available. See <a href="#Intrinsic">Intrinsic built-in support</a>.</p>
|
||
|
||
</blockquote>
|
||
|
||
<p><b>Why bother with endianness?</b></p>
|
||
<blockquote>
|
||
<p>Binary data portability is the primary use case.</p>
|
||
</blockquote>
|
||
<p><b>Does endianness have any uses outside of portable binary file or network
|
||
I/O formats?</b> </p>
|
||
<blockquote>
|
||
<p>Using the unaligned integer types to save internal or external
|
||
memory space is a minor secondary use case.</p>
|
||
</blockquote>
|
||
<p><b>Why bother with binary I/O? Why not just use C++ Standard Library stream
|
||
inserters and extractors?</b></p>
|
||
<blockquote>
|
||
<p>Binary arithmetic data is smaller and therefore I/O is faster and file sizes
|
||
are smaller. Transfer between systems is less expensive. Standard interchange
|
||
formats often specify binary arithmetic data.</p>
|
||
<p>Furthermore, binary arithmetic data is of fixed size, and so fixed-size disk
|
||
records are possible without padding, easing sorting and allowing direct access.
|
||
Disadvantages, such as the inability to use text utilities on the resulting
|
||
files, limit usefulness to applications where the binary I/O advantages are
|
||
paramount.</p>
|
||
</blockquote>
|
||
|
||
<p><b>Which is better, big-endian or little-endian?</b></p>
|
||
<blockquote>
|
||
<p>Big-endian tends to be a
|
||
bit more of an industry standard, but little-endian may be preferred for
|
||
applications that run primarily Intel/AMD on x86, x64, and other little-endian
|
||
CPU's. The <a href="http://en.wikipedia.org/wiki/Endian">Wikipedia</a> article
|
||
gives more pros and cons.</p>
|
||
</blockquote>
|
||
|
||
<p><b>Why is only big, little, and native endianness supported?</b></p>
|
||
<blockquote>
|
||
<p>These are the only endian schemes that have any practical value today. PDP-11
|
||
and the other middle endian approaches are interesting historical curiosities
|
||
but have no relevance to C++ developers.</p>
|
||
</blockquote>
|
||
|
||
<p><b>What are the limitations of floating point support?</b></p>
|
||
|
||
<blockquote>
|
||
|
||
<p>The only supported types are four byte <code>float</code> and eight byte
|
||
<code>double</code>. Even after endianness has been accounted for, floating
|
||
point values will not be portable between systems that use different floating
|
||
point formats. Systems where the integer endianness differs from floating point
|
||
endianness are not supported.</p>
|
||
|
||
</blockquote>
|
||
|
||
<p><b>What are the limitations of integer support?</b></p>
|
||
|
||
<blockquote>
|
||
|
||
<p>Tests have only been
|
||
performed on machines that use two's complement arithmetic. The Endian
|
||
conversion functions support 16, 32, and 64-bit aligned integers only. The
|
||
Endian types support 8, 16, 24, 32, 40, 48, 56, and 64-bit unaligned integers
|
||
and 16, 32, and 64-bit aligned integers.</p>
|
||
|
||
</blockquote>
|
||
|
||
<h2><a name="Release-history">Release history</a></h2>
|
||
<h3>Changes since formal review</h3>
|
||
<ul>
|
||
<li>Headers have been renamed to endian/types.hpp and endian/conversion.hpp.
|
||
Infrastructure file names were changed accordingly.</li>
|
||
<li>The endian types and endian conversion functions now support 32-bit (<code>float)</code> and
|
||
64-bit <code>(double)</code> floating point, as requested.</li>
|
||
<li>Both the endian types and endian conversion functions now support UDTs, as requested.</li>
|
||
<li>The endian type aliases have been renamed,
|
||
using a naming pattern that is consistent for both integer and floating point.</li>
|
||
<li>The conversion functions have been much revised,
|
||
refactored, and otherwise improved based on review comments.<ul>
|
||
<li>Functions have been renamed to clarify their functionality.</li>
|
||
<li>Both return-by-value and modify-in-place interfaces are provided, as
|
||
requested.</li>
|
||
<li>Synonyms for the BSD byte swapping function names popularized by OS X
|
||
and Linux are provided, so that that developers already used to these name
|
||
can continue to use them if they wish.</li>
|
||
<li>In addition to the named-endianness functions, functions that perform
|
||
compile-time (via template) and run-time (via function argument) dispatch
|
||
are now provided, as requested.</li>
|
||
</ul>
|
||
</li>
|
||
<li>Compiler (Clang, GCC, VisualC++, etc.) intrinsics and built-in functions
|
||
are used in the implementation where appropriate, as requested.</li>
|
||
<li>For the endian types, the implementation uses the endian conversion functions,
|
||
and thus the intrinsics,
|
||
as requested.</li>
|
||
<li>C++11 features such as <code>noexcept</code> are now used, while still
|
||
supporting C++03 compilers.</li>
|
||
<li>Acknowledgements have been updated.</li>
|
||
<li>Headers have been reorganized to make them easier to read,
|
||
with a synopsis at the front and implementation following, as requested.</li>
|
||
<li>Documentation has been revised to address most, but not all, concerns
|
||
raised during formal review.</li>
|
||
</ul>
|
||
|
||
<h2><a name="Acknowledgements">Acknowledgements</a></h2>
|
||
<p>Comments and suggestions were received from Adder, Benaka Moorthi,
|
||
Christopher Kohlhoff, Cliff Green, Daniel James, Gennaro Proto, Giovanni Piero
|
||
Deretta, Gordon Woodhull, dizzy, Hartmut Kaiser, Jeff Flinn, John Filo, John
|
||
Maddock, Kim Barrett, Marsh Ray, Martin Bonner, Mathias Gaunard, Matias
|
||
Capeletto, Neil Mayhew, Paul Bristow, Pierre Talbot, Phil Endecott, Pyry Jahkola,
|
||
Rene Rivera, Robert Stewart, Roland Schwarz, Scott McMurray, Sebastian Redl, Tim
|
||
Blechmann, Tim Moore, tymofey, Tomas Puverle, Vincente Botet, Yuval Ronen and
|
||
Vitaly Budovski,.</p>
|
||
<hr>
|
||
<p>Last revised:
|
||
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->16 April, 2014<!--webbot bot="Timestamp" endspan i-checksum="29929" --></p>
|
||
<p>© Copyright Beman Dawes, 2011, 2013</p>
|
||
<p>Distributed under the Boost Software License, Version 1.0. See
|
||
<a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/ LICENSE_1_0.txt</a></p>
|
||
|
||
<p> </p>
|
||
|
||
</body>
|
||
|
||
</html> |