<li><a href="#crc_optimal">Optimized CRC Computer</a></li>
<li><a href="#usage">Computer Usage</a></li>
<li><a href="#crc_func">CRC Function</a></li>
- <li><a href="#a_crc_func">Augmented-CRC Functions</a></li>
+ <li><a href="#a_crc_func">Augmented-CRC Function</a></li>
<li><a href="#crc_ex">Pre-Defined CRC Samples</a></li>
<li><a href="#references">References</a></li>
<li><a href="#credits">Credits</a>
template < std::size_t Bits, <em>impl_def</em> TruncPoly >
typename uint_t<Bits>::fast augmented_crc( void const *buffer,
std::size_t byte_count,
- typename uint_t<Bits>::fast initial_remainder );
-
-template < std::size_t Bits, <em>impl_def</em> TruncPoly >
- typename uint_t<Bits>::fast augmented_crc( void const *buffer,
- std::size_t byte_count );
+ typename uint_t<Bits>::fast initial_remainder = 0u );
typedef crc_optimal<16, 0x8005, 0, 0, true, true> crc_16_type;
typedef crc_optimal<16, 0x1021, 0xFFFF, 0, false, false> crc_ccitt_type;
<p>See <cite><a href="http://www.ross.net/crc/crcpaper.html">A
Painless Guide to CRC Error Detection Algorithms</a></cite> for complete
information. A clearer guide is at the <a
-href="http://www.netrino.com/Connecting/2000-01/">Easier Said Than
-Done</a> web page.</p>
+href="http://www.netrino.com/Embedded-Systems/How-To/CRC-Calculation-C-Code">CRC
+Implementation Code in C</a> web page.</p>
<h3><a name="parameters">CRC Parameters</a></h3>
optimized CRC computer (<a href="#crc_optimal">see above</a>). In fact,
such a computer is used to implement this function.</p>
-<h2><a name="a_crc_func">Augmented-CRC Functions</a></h2>
+<h2><a name="a_crc_func">Augmented-CRC Function</a></h2>
<blockquote><pre>template < std::size_t Bits, <em>impl_def</em> TruncPoly >
typename boost::uint_t<Bits>::fast
boost::augmented_crc( void const *buffer, std::size_t byte_count,
- typename boost::uint_t<Bits>::fast initial_remainder );
-
-template < std::size_t Bits, <em>impl_def</em> TruncPoly >
-typename boost::uint_t<Bits>::fast
-boost::augmented_crc( void const *buffer, std::size_t byte_count );
+ typename boost::uint_t<Bits>::fast initial_remainder = 0u );
</pre></blockquote>
<p>All the other CRC-computing function or class templates work assuming
that the division steps start immediately on the first message bits.
-The two <code>boost::augmented_crc</code> function templates have a
+The <code>boost::augmented_crc</code> function template has a
different division order. Instead of combining (<i>via</i> bitwise
exclusive-or) the current message bit with the highest bit of a separate
remainder, these templates shift a new message bit into the low bit of a
CRC can only be extracted after feeding enough zero bits (the same count
as the register size) after the message bits.</p>
-<p>The template parameters of both versions of the function template are
+<p>The template parameters of the function template are
the CRC's bit size (<code>Bits</code>) and the truncated polynominal
-(<code>TruncPoly</code>). The version of the function template that
-takes two arguments calls the three-argument version with the
-<var>initial_remainder</var> parameter filled as zero. Both versions
-work on the data block starting at the address <var>buffer</var> for
-<var>byte_count</var> bytes.</p>
+(<code>TruncPoly</code>). The function parameters are the starting address of
+the data block to be worked on (<var>buffer</var>), the number of bytes in that
+data block (<var>byte_count</var>), and the incoming value of the remainder
+(<var>initial_remainder</var>). That last parameter defaults to zero if it is
+ommitted.</p>
-<p>These function templates are useful if the bytes of the CRC directly
+<p>This function template is useful if the bytes of the CRC directly
follow the message's bytes. First, set the bytes of where the CRC will
go to zero. Then use <code>augmented_crc</code> over the augmented
message, <i>i.e.</i> the message bytes and the appended CRC bytes. Then
<dt>Michael Barr (<a
href="mailto:mbarr@netrino.com">mbarr@netrino.com</a>)
<dd>Wrote <a
- href="http://www.netrino.com/Connecting/2000-01/">Easier Said
- Than Done</a>, a less-confusing guide to implementing CRC
+ href="http://www.netrino.com/Embedded-Systems/How-To/CRC-Calculation-C-Code">CRC
+ Implementation Code in C</a>, a less-confusing guide to implementing CRC
algorithms. (Originally published as "Slow and Steady
Never Lost the Race" in the January 2000 issue of <cite><a
href="http://www.embedded.com/">Embedded Systems
- Programming</a></cite>, pages 37–46.)
+ Programming</a></cite>, pages 37–46. The web version used to be
+ known as <cite><a href="http://www.netrino.com/Connecting/2000-01/">Easier
+ Said Than Done</a></cite>.)
<dt>Daryle Walker
<dd>Started the library and contributed the theoretical and optimal
<h3><a name="history">History</a></h3>
<dl>
+ <dt>18 Dec 2011, Daryle Walker
+ <dd>Folded the two versions of <code>boost::augmented_crc</code> together.
+
<dt>15 Jun 2003, Daryle Walker
<dd>Added example program.
<hr>
-<p>Revised: 15 June 2003</p>
+<p>Revised: 18 December 2011</p>
-<p>Copyright 2001, 2003 Daryle Walker. Use, modification, and distribution
+<p>Copyright 2001, 2003, 2011 Daryle Walker. Use, modification, and distribution
are subject to the Boost Software License, Version 1.0. (See accompanying
file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or a copy at
<<a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>>.)</p>
projects / ceph.git / blobdiff