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Folded both versions of boost::augmented_crc into a single one with a defaulted trailing argument; updated a web link.

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[SVN r76059]
This commit is contained in:
Daryle Walker
2011-12-19 05:20:39 +00:00
parent 6da2cbe97b
commit d98c9fa072
2 changed files with 27 additions and 53 deletions
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crc.html
+24 -27
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@@ -32,7 +32,7 @@ function templates to compute a CRC in one step.</p>
<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>
@@ -69,11 +69,7 @@ template &lt; std::size_t Bits, <em>impl_def</em> TruncPoly,
template &lt; std::size_t Bits, <em>impl_def</em> TruncPoly &gt;
typename uint_t&lt;Bits&gt;::fast augmented_crc( void const *buffer,
std::size_t byte_count,
typename uint_t&lt;Bits&gt;::fast initial_remainder );
template &lt; std::size_t Bits, <em>impl_def</em> TruncPoly &gt;
typename uint_t&lt;Bits&gt;::fast augmented_crc( void const *buffer,
std::size_t byte_count );
typename uint_t&lt;Bits&gt;::fast initial_remainder = 0u );
typedef crc_optimal&lt;16, 0x8005, 0, 0, true, true&gt; crc_16_type;
typedef crc_optimal&lt;16, 0x1021, 0xFFFF, 0, false, false&gt; crc_ccitt_type;
@@ -118,8 +114,8 @@ carries) for the coefficents.</p>
<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>
@@ -432,21 +428,17 @@ parameters are passed through template arguments, identical to the
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 &lt; std::size_t Bits, <em>impl_def</em> TruncPoly &gt;
typename boost::uint_t&lt;Bits&gt;::fast
boost::augmented_crc( void const *buffer, std::size_t byte_count,
typename boost::uint_t&lt;Bits&gt;::fast initial_remainder );
template &lt; std::size_t Bits, <em>impl_def</em> TruncPoly &gt;
typename boost::uint_t&lt;Bits&gt;::fast
boost::augmented_crc( void const *buffer, std::size_t byte_count );
typename boost::uint_t&lt;Bits&gt;::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
@@ -456,15 +448,15 @@ any of the actual message bits are processed. To compensate, the real
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
@@ -576,12 +568,14 @@ library is concerned with CRC implementation, and not with determining
<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 &quot;Slow and Steady
Never Lost the Race&quot; in the January 2000 issue of <cite><a
href="http://www.embedded.com/">Embedded Systems
Programming</a></cite>, pages 37&ndash;46.)
Programming</a></cite>, pages 37&ndash;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
@@ -615,6 +609,9 @@ interface, algorithms, and bug reports:</p>
<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.
@@ -624,9 +621,9 @@ interface, algorithms, and bug reports:</p>
<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
&lt;<a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>&gt;.)</p>
include/boost/crc.hpp
+3 -26
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@@ -86,12 +86,7 @@ template < std::size_t Bits, BOOST_CRC_PARM_TYPE TruncPoly,
template < std::size_t Bits, BOOST_CRC_PARM_TYPE TruncPoly >
typename uint_t<Bits>::fast augmented_crc( void const *buffer,
std::size_t byte_count, typename uint_t<Bits>::fast initial_remainder
BOOST_ACRC_DUMMY_PARM_TYPE );
template < std::size_t Bits, BOOST_CRC_PARM_TYPE TruncPoly >
typename uint_t<Bits>::fast augmented_crc( void const *buffer,
std::size_t byte_count
std::size_t byte_count, typename uint_t<Bits>::fast initial_remainder = 0u
BOOST_ACRC_DUMMY_PARM_TYPE );
typedef crc_optimal<16, 0x8005, 0, 0, true, true> crc_16_type;
@@ -888,7 +883,7 @@ crc
}
// Augmented-message CRC computation function definitions ------------------//
// Augmented-message CRC computation function definition -------------------//
template < std::size_t Bits, BOOST_CRC_PARM_TYPE TruncPoly >
typename uint_t<Bits>::fast
@@ -896,7 +891,7 @@ augmented_crc
(
void const * buffer,
std::size_t byte_count,
typename uint_t<Bits>::fast initial_remainder
typename uint_t<Bits>::fast initial_remainder // = 0u
BOOST_ACRC_DUMMY_INIT
)
{
@@ -922,24 +917,6 @@ augmented_crc
return rem & detail::low_bits_mask_c<Bits>::value;
}
template < std::size_t Bits, BOOST_CRC_PARM_TYPE TruncPoly >
inline
typename uint_t<Bits>::fast
augmented_crc
(
void const * buffer,
std::size_t byte_count
BOOST_ACRC_DUMMY_INIT
)
{
// The last function argument has its type specified so the other version of
// augmented_crc will be called. If the cast wasn't in place, and the
// BOOST_ACRC_DUMMY_INIT added a third argument (for a workaround), the "0"
// would match as that third argument, leading to infinite recursion.
return augmented_crc<Bits, TruncPoly>( buffer, byte_count,
static_cast<typename uint_t<Bits>::fast>(0) );
}
} // namespace boost