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636 lines
25 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Boost CRC Library Documentation</title>
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</head>
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<body text="black" bgcolor="white" link="blue" vlink="purple" alink="red">
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<h1><img src="../../boost.png" alt="boost.png (6897 bytes)"
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align="middle" width="277" height="86">Header <cite><<a
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href="../../boost/crc.hpp">boost/crc.hpp</a>></cite></h1>
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<p>The header <cite><<a
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href="../../boost/crc.hpp">boost/crc.hpp</a>></cite> supplies two
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class templates in namespace <code>boost</code>. These templates define
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objects that can compute the <dfn>CRC</dfn>, or cyclic redundancy code
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(or check), of a given stream of data. The header also supplies
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function templates to compute a CRC in one step.</p>
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<h2><a name="contents">Contents</a></h2>
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<ol>
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<li><a href="#contents">Contents</a></li>
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<li><a href="#header">Header Synopsis</a></li>
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<li><a href="#rationale">Rationale</a></li>
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<li><a href="#background">Background</a>
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<ul>
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<li><a href="#parameters">CRC Parameters</a></li>
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</ul></li>
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<li><a href="#crc_basic">Theoretical CRC Computer</a></li>
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<li><a href="#crc_optimal">Optimized CRC Computer</a></li>
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<li><a href="#usage">Computer Usage</a></li>
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<li><a href="#crc_func">CRC Function</a></li>
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<li><a href="#a_crc_func">Augmented-CRC Functions</a></li>
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<li><a href="#crc_ex">Pre-Defined CRC Samples</a></li>
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<li><a href="#references">References</a></li>
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<li><a href="#credits">Credits</a>
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<ul>
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<li><a href="#contributors">Contributors</a></li>
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<li><a href="#acknowledgements">Acknowledgements</a></li>
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<li><a href="#history">History</a></li>
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</ul></li>
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</ol>
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<h2><a name="header">Header Synopsis</a></h2>
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<blockquote><pre>#include <boost/integer.hpp> <i>// for boost::uint_t</i>
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#include <cstddef> <i>// for std::size_t</i>
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namespace boost
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{
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template < std::size_t Bits >
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class crc_basic;
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template < std::size_t Bits, <em>impl_def</em> TruncPoly = 0u,
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<em>impl_def</em> InitRem = 0u,
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<em>impl_def</em> FinalXor = 0u, bool ReflectIn = false,
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bool ReflectRem = false >
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class crc_optimal;
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template < std::size_t Bits, <em>impl_def</em> TruncPoly,
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<em>impl_def</em> InitRem, <em>impl_def</em> FinalXor,
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bool ReflectIn, bool ReflectRem >
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typename uint_t<Bits>::fast crc( void const *buffer,
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std::size_t byte_count );
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template < std::size_t Bits, <em>impl_def</em> TruncPoly >
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typename uint_t<Bits>::fast augmented_crc( void const *buffer,
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std::size_t byte_count,
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typename uint_t<Bits>::fast initial_remainder );
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template < std::size_t Bits, <em>impl_def</em> TruncPoly >
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typename uint_t<Bits>::fast augmented_crc( void const *buffer,
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std::size_t byte_count );
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typedef crc_optimal<16, 0x8005, 0, 0, true, true> crc_16_type;
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typedef crc_optimal<16, 0x1021, 0xFFFF, 0, false, false> crc_ccitt_type;
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typedef crc_optimal<16, 0x8408, 0, 0, true, true> crc_xmodem_type;
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typedef crc_optimal<32, 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true, true>
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crc_32_type;
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}
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</pre></blockquote>
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<p>The implementation-defined type <var>impl_def</var> stands for the
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quickest-to-manipulate built-in unsigned integral type that can
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represent at least <var>Bits</var> bits.</p>
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<h2><a name="rationale">Rationale</a></h2>
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<p>A common error detection technique, especially with electronic
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communications, is an appended checksum. The transmitter sends its data
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bits, followed by the bits of the checksum. The checksum is based on
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operations done on the data bit stream. The receiver applies the same
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operations on the bits it gets, and then gets the checksum. If the
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computed checksum doesn't match the received checksum, then an error
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ocurred in the transmission. There is the slight chance that the error
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is only in the checksum, and an actually-correct data stream is
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rejected. There is also the chance of an error occurring that does not
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change the checksum, making that error invisible. CRC is a common
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checksum type, used for error detection for hardware interfaces and
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encoding formats.</p>
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<h2><a name="background">Background</a></h2>
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<p>CRCs work by computing the remainder of a modulo-2 polynominal
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division. The message is treated as the (binary) coefficents of a long
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polynominal for the dividend, with the earlier bits of the message fed
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first as the polynominal's highest coefficents. A particular CRC
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algorithm has another polynominal associated with it to be used as the
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divisor. The quotient is ignored. The remainder of the division
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considered the checksum. However, the division uses modulo-2 rules (no
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carries) for the coefficents.</p>
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<p>See <cite><a href="http://www.ross.net/crc/crcpaper.html">A
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Painless Guide to CRC Error Detection Algorithms</a></cite> for complete
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information. A clearer guide is at the <a
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href="http://www.netrino.com/Connecting/2000-01/">Easier Said Than
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Done</a> web page.</p>
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<h3><a name="parameters">CRC Parameters</a></h3>
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<dl>
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<dt>Truncated polynominal
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<dd>The divisor polynominal has a degree one bit larger than the
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checksum (remainder) size. That highest bit is always one, so
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it is ignored when describing a particular CRC type. Excluding
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this bit makes the divisor fit in the same data type as the
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checksum.
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<dt>Initial remainder
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<dd>The interim CRC remainder changes as each bit is processed.
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Usually, the interim remainder starts at zero, but some CRCs use
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a different initial value to avoid "blind spots." A
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blind spot is when a common sequence of message bits does not
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change certain interim remainder values.
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<dt>Final XOR value
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<dd>A CRC remainder can be combined with a defined value, <i>via</i>
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a bitwise exclusive-or operation, before being returned to the
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user. The value is usually zero, meaning the interim remainder
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is returned unchanged. The other common value is an all-ones
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value, meaning that the bitwise complement of the interim
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remainder is returned.
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<dt>Reflected input
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<dd>A message's bits are usually fed a byte at a time, with the
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highest bits of the byte treated as the higher bits of the
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dividend polynominal. Some CRCs reflect the bits (about the
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byte's center, so the first and last bits are switched,
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<i>etc.</i>) before feeding.
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<dt>Reflected (remainder) output
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<dd>Some CRCs return the reflection of the interim remainder (taking
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place <em>before</em> the final XOR value stage).
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</dl>
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<h2><a name="crc_basic">Theoretical CRC Computer</a></h2>
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<blockquote><pre>template < std::size_t Bits >
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class boost::crc_basic
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{
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public:
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// Type
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typedef <em>implementation_defined</em> value_type;
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// Constant reflecting template parameter
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static std::size_t const bit_count = Bits;
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// Constructor
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explicit crc_basic( value_type truncated_polynominal,
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value_type initial_remainder = 0, value_type final_xor_value = 0,
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bool reflect_input = false, bool reflect_remainder = false );
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// Internal Operations
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value_type get_truncated_polynominal() const;
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value_type get_initial_remainder() const;
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value_type get_final_xor_value() const;
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bool get_reflect_input() const;
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bool get_reflect_remainder() const;
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value_type get_interim_remainder() const;
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void reset( value_type new_rem );
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void reset();
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// External Operations
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void process_bit( bool bit );
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void process_bits( unsigned char bits, std::size_t bit_count );
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void process_byte( unsigned char byte );
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void process_block( void const *bytes_begin, void const *bytes_end );
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void process_bytes( void const *buffer, std::size_t byte_count );
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value_type checksum() const;
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};
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</pre></blockquote>
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<p>The <code>value_type</code> is the smallest built-in type that can
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hold the specified (by <code>Bits</code>) number of bits. This should
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be <code>boost::uint_t<Bits>::least</code>, see the <a
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href="../integer/doc/html/boost_integer/integer.html">documentation for integer type
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selection</a> for details.</p>
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<p>This implementation is slow since it computes its CRC the same way as
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in theory, bit by bit. No optimizations are performed. It wastes space
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since most of the CRC parameters are specified at run-time as
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constructor parameters.</p>
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<h2><a name="crc_optimal">Optimized CRC Computer</a></h2>
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<blockquote><pre>template < std::size_t Bits, <em>impl_def</em> TruncPoly,
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<em>impl_def</em> InitRem, <em>impl_def</em> FinalXor,
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bool ReflectIn, bool ReflectRem >
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class boost::crc_optimal
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{
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public:
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// Type
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typedef <em>implementation_defined</em> value_type;
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// Constants reflecting template parameters
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static std::size_t const bit_count = Bits;
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static value_type const truncated_polynominal = TruncPoly;
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static value_type const initial_remainder = InitRem;
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static value_type const final_xor_value = FinalXor;
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static bool const reflect_input = ReflectIn;
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static bool const reflect_remainder = ReflectRem;
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// Constructor
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explicit crc_optimal( value_type init_rem = InitRem );
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// Internal Operations
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value_type get_truncated_polynominal() const;
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value_type get_initial_remainder() const;
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value_type get_final_xor_value() const;
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bool get_reflect_input() const;
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bool get_reflect_remainder() const;
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value_type get_interim_remainder() const;
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void reset( value_type new_rem = InitRem );
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// External Operations
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void process_byte( unsigned char byte );
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void process_block( void const *bytes_begin, void const *bytes_end );
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void process_bytes( void const *buffer, std::size_t byte_count );
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value_type checksum() const;
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// Operators
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void operator ()( unsigned char byte );
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value_type operator ()() const;
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};
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</pre></blockquote>
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<p>The <code>value_type</code> is the quickest-to-manipulate built-in
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type that can hold at least the specified (by <code>Bits</code>) number
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of bits. This should be <code>boost::uint_t<Bits>::fast</code>.
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See the <a href="../integer/doc/html/boost_integer/integer.html">integer type selection
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documentation</a> for details. The <code>TruncPoly</code>,
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<code>InitRem</code>, and <code>FinalXor</code> template parameters also
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are of this type.</p>
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<p>This implementation is fast since it uses as many optimizations as
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practical. All of the CRC parameters are specified at compile-time as
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template parameters. No individual bits are considered; only whole
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bytes are passed. A table of interim CRC values versus byte values is
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pre-computed when the first object using a particular bit size,
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truncated polynominal, and input reflection state is processed.</p>
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<h2><a name="usage">Computer Usage</a></h2>
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<p>The two class templates have different policies on where the CRC's
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parameters go. Both class templates use the number of bits in the CRC
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as the first template parameter. The theoretical computer class
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template has the bit count as its only template parameter, all the other
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CRC parameters are entered through the constructor. The optimized
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computer class template obtains all its CRC parameters as template
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parameters, and instantiated objects are usually
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default-constructed.</p>
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<p>The CRC parameters can be inspected at run-time with the following
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member functions: <code>get_truncated_polynominal</code>,
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<code>get_initial_remainder</code>, <code>get_final_xor_value</code>,
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<code>get_reflect_input</code>, and <code>get_reflect_remainder</code>.
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The fast computer also provides compile-time constants for its CRC
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parameters.</p>
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<p>The <code>get_interim_remainder</code> member function returns the
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internal state of the CRC remainder. It represents the unreflected
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remainder of the last division. Saving an interim remainder allows the
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freezing of CRC processing, as long as the other CRC parameters and the
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current position of the bit stream are saved. Restarting a frozen
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stream involves constructing a new computer with the most of the old
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computer's parameters. The only change is to use the frozen remainder
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as the new computer's initial remainder. Then the interrupted bit
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stream can be fed as if nothing happened. The fast CRC computer has a
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special constructor that takes one argument, an interim remainder, for
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this purpose (overriding the initial remainder CRC parameter).</p>
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<p>The <code>reset</code> member functions reset the internal state of
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the CRC remainder to the given value. If no value is given, then the
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internal remainder is set to the initial remainder value when the object
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was created. The remainder must be unreflected. When a CRC calculation
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is finished, calling <code>reset</code> lets the object be reused for a
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new session.</p>
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<p>After any construction, both CRC computers work the same way.
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Feeding new data to a computer is in a seperate operation(s) from
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extracting the current CRC value from the computer. The following table
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lists the feeding and extracting operations.</p>
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<table cellpadding="5" border="1">
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<caption>Regular CRC Operations</caption>
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<tr>
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<th>Operation</th>
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<th>Description</th>
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</tr>
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<tr>
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<td><code>void process_bit( bool bit );</code></td>
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<td>Feeds the single <var>bit</var> to the computer, updating
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the interim CRC. It is only defined for the slow CRC
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computer.</td>
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</tr>
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<tr>
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<td><code>void process_bits( unsigned char bits, std::size_t
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bit_count );</code></td>
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<td>Acts as applying <code>process_bit</code> to the lowest
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<var>bit_count</var> bits given in <var>bits</var>, most
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significant relevant bit first. The results are undefined
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|
if <var>bit_count</var> exceeds the number of bits per byte.
|
||
|
|
It is only defined for the slow CRC computer.</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>void process_byte( unsigned char byte );</code></td>
|
||
|
|
<td>Acts as applying <code>process_bit</code> to the all the
|
||
|
|
bits in <var>byte</var>. If reflection is not desired, the
|
||
|
|
bits are fed from the most to least significant. The bits
|
||
|
|
are fed in the opposite order if reflection is desired.</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>void process_block( void const *bytes_begin, void
|
||
|
|
const *bytes_end );</code></td>
|
||
|
|
<td>Acts as applying <code>process_byte</code> to each byte in
|
||
|
|
the given memory block. This memory block starts at
|
||
|
|
<var>bytes_begin</var> and finishes before
|
||
|
|
<var>bytes_end</var>. The bytes are processed in that
|
||
|
|
order.</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>void process_bytes( void const *buffer, std::size_t
|
||
|
|
byte_count );</code></td>
|
||
|
|
<td>Acts as applying <code>process_byte</code> to each byte in
|
||
|
|
the given memory block. This memory block starts at
|
||
|
|
<var>buffer</var> and lasts for <var>byte_count</var> bytes.
|
||
|
|
The bytes are processed in ascending order.</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>value_type checksum() const;</code></td>
|
||
|
|
<td>Returns the CRC checksum of the data passed in so far,
|
||
|
|
possibly after applying the remainder-reflection and
|
||
|
|
exclusive-or operations.</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>void operator ()( unsigned char byte );</code></td>
|
||
|
|
<td>Calls <code>process_byte</code>. This member function lets
|
||
|
|
its object act as a (stateful) function object. It is only
|
||
|
|
defined for the fast CRC computer.</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>value_type operator ()() const;</code></td>
|
||
|
|
<td>Calls <code>checksum</code>. This member function lets
|
||
|
|
its object act as a generator function object. It is only
|
||
|
|
defined for the fast CRC computer.</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<p>You can use them like this:</p>
|
||
|
|
|
||
|
|
<blockquote><pre>#include <boost/crc.hpp> <i>// for boost::crc_basic, boost::crc_optimal</i>
|
||
|
|
#include <boost/cstdint.hpp> <i>// for boost::uint16_t</i>
|
||
|
|
|
||
|
|
#include <algorithm> <i>// for std::for_each</i>
|
||
|
|
#include <cassert> <i>// for assert</i>
|
||
|
|
#include <cstddef> <i>// for std::size_t</i>
|
||
|
|
#include <iostream> <i>// for std::cout</i>
|
||
|
|
#include <ostream> <i>// for std::endl</i>
|
||
|
|
|
||
|
|
|
||
|
|
// Main function
|
||
|
|
int
|
||
|
|
main ()
|
||
|
|
{
|
||
|
|
// This is "123456789" in ASCII
|
||
|
|
unsigned char const data[] = { 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
|
||
|
|
0x38, 0x39 };
|
||
|
|
std::size_t const data_len = sizeof( data ) / sizeof( data[0] );
|
||
|
|
|
||
|
|
// The expected CRC for the given data
|
||
|
|
boost::uint16_t const expected = 0x29B1;
|
||
|
|
|
||
|
|
// Simulate CRC-CCITT
|
||
|
|
boost::crc_basic<16> crc_ccitt1( 0x1021, 0xFFFF, 0, false, false );
|
||
|
|
crc_ccitt1.process_bytes( data, data_len );
|
||
|
|
assert( crc_ccitt1.checksum() == expected );
|
||
|
|
|
||
|
|
// Repeat with the optimal version (assuming a 16-bit type exists)
|
||
|
|
boost::crc_optimal<16, 0x1021, 0xFFFF, 0, false, false> crc_ccitt2;
|
||
|
|
crc_ccitt2 = std::for_each( data, data + data_len, crc_ccitt2 );
|
||
|
|
assert( crc_ccitt2() == expected );
|
||
|
|
|
||
|
|
std::cout << "All tests passed." << std::endl;
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
</pre></blockquote>
|
||
|
|
|
||
|
|
<h2><a name="crc_func">CRC Function</a></h2>
|
||
|
|
|
||
|
|
<blockquote><pre>template < std::size_t Bits, <em>impl_def</em> TruncPoly,
|
||
|
|
<em>impl_def</em> InitRem, <em>impl_def</em> FinalXor,
|
||
|
|
bool ReflectIn, bool ReflectRem >
|
||
|
|
typename boost::uint_t<Bits>::fast
|
||
|
|
boost::crc( void const *buffer, std::size_t byte_count );
|
||
|
|
</pre></blockquote>
|
||
|
|
|
||
|
|
<p>The <code>boost::crc</code> function template computes the CRC of a
|
||
|
|
given data block. The data block starts at the address given by
|
||
|
|
<var>buffer</var> and lasts for <var>byte_count</var> bytes. The CRC
|
||
|
|
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>
|
||
|
|
|
||
|
|
<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 );
|
||
|
|
</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
|
||
|
|
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
|
||
|
|
remainder register as the highest bit is shifted out. The new method
|
||
|
|
means that the bits in the inital remainder value are processed before
|
||
|
|
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
|
||
|
|
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>
|
||
|
|
|
||
|
|
<p>These function templates are 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
|
||
|
|
assign the result to the CRC. To later check a received message, either
|
||
|
|
use <code>augmented_crc</code> (with the same parameters as
|
||
|
|
transmission, of course) on the received <em>unaugmented</em> message
|
||
|
|
and check if the result equals the CRC, or use
|
||
|
|
<code>augmented_crc</code> on the received <em>augmented</em> message
|
||
|
|
and check if the result equals zero. Note that the CRC has to be stored
|
||
|
|
with the more-significant bytes first (big-endian).</p>
|
||
|
|
|
||
|
|
<p>Interruptions in the CRC data can be handled by feeding the result of
|
||
|
|
<code>augmented_crc</code> of the previous data block as the
|
||
|
|
<var>initial_remainder</var> when calling <code>augmented_crc</code> on
|
||
|
|
the next data block. Remember that the actual CRC can only be
|
||
|
|
determined after feeding the augmented bytes. Since this method uses
|
||
|
|
modulo-2 polynominal division at its most raw, neither final XOR values
|
||
|
|
nor reflection can be used.</p>
|
||
|
|
|
||
|
|
<p>Note that for the same CRC system, the initial remainder for
|
||
|
|
augmented message method will be different than for the unaugmented
|
||
|
|
message method. The main exception is zero; if the augmented-CRC
|
||
|
|
algorithm uses a zero initial remainder, the equivalent unaugmented-CRC
|
||
|
|
algorithm will also use a zero initial remainder. Given an initial
|
||
|
|
remainder for a augmented-CRC algorithm, the result from processing just
|
||
|
|
zero-valued CRC bytes without any message bytes is the equivalent inital
|
||
|
|
remainder for the unaugmented-CRC algorithm. An example follows:</p>
|
||
|
|
|
||
|
|
<blockquote><pre>#include <boost/crc.hpp> <i>// for boost::crc_basic, boost::augmented_crc</i>
|
||
|
|
#include <boost/cstdint.hpp> <i>// for boost::uint16_t</i>
|
||
|
|
|
||
|
|
#include <cassert> <i>// for assert</i>
|
||
|
|
#include <iostream> <i>// for std::cout</i>
|
||
|
|
#include <ostream> <i>// for std::endl</i>
|
||
|
|
|
||
|
|
|
||
|
|
// Main function
|
||
|
|
int
|
||
|
|
main ()
|
||
|
|
{
|
||
|
|
using boost::uint16_t;
|
||
|
|
using boost::augmented_crc;
|
||
|
|
|
||
|
|
uint16_t data[6] = { 2, 4, 31, 67, 98, 0 };
|
||
|
|
uint16_t const init_rem = 0x123;
|
||
|
|
|
||
|
|
uint16_t crc1 = augmented_crc<16, 0x8005>( data, sizeof(data), init_rem );
|
||
|
|
|
||
|
|
uint16_t const zero = 0;
|
||
|
|
uint16_t const new_init_rem = augmented_crc<16, 0x8005>( &zero, sizeof(zero) );
|
||
|
|
|
||
|
|
boost::crc_basic<16> crc2( 0x8005, new_init_rem );
|
||
|
|
crc2.process_block( data, &data[5] ); // don't include CRC
|
||
|
|
assert( crc2.checksum() == crc1 );
|
||
|
|
|
||
|
|
std::cout << "All tests passed." << std::endl;
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
</pre></blockquote>
|
||
|
|
|
||
|
|
<h2><a name="crc_ex">Pre-Defined CRC Samples</a></h2>
|
||
|
|
|
||
|
|
<p>Four sample CRC types are given, representing several common CRC
|
||
|
|
algorithms. For example, computations from <code>boost::crc_32_type</code>
|
||
|
|
can be used for implementing the PKZip standard. Note that, in general, this
|
||
|
|
library is concerned with CRC implementation, and not with determining
|
||
|
|
"good" sets of CRC parameters.</p>
|
||
|
|
|
||
|
|
<table cellpadding="5" border="1">
|
||
|
|
<caption>Common CRCs</caption>
|
||
|
|
<tr>
|
||
|
|
<th>Algorithm</th>
|
||
|
|
<th>Example Protocols</th>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>crc_16_type</code></td>
|
||
|
|
<td>BISYNCH, ARC</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>crc_ccitt_type</code></td>
|
||
|
|
<td>designated by CCITT (Comité Consultatif International
|
||
|
|
Télégraphique et Téléphonique)</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>crc_xmodem_type</code></td>
|
||
|
|
<td>XMODEM</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td><code>crc_32_type</code></td>
|
||
|
|
<td>PKZip, AUTODIN II, Ethernet, FDDI</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
|
||
|
|
<h2><a name="references">References</a></h2>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>The CRC header itself: <cite><a href="../../boost/crc.hpp">crc.hpp</a></cite>
|
||
|
|
<li>Some test code: <cite><a href="test/crc_test.cpp">crc_test.cpp</a></cite>
|
||
|
|
<li>Some example code: <cite><a href="crc_example.cpp">crc_example.cpp</a></cite>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<h2><a name="credits">Credits</a></h2>
|
||
|
|
|
||
|
|
<h3><a name="contributors">Contributors</a></h3>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<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
|
||
|
|
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.)
|
||
|
|
|
||
|
|
<dt>Daryle Walker
|
||
|
|
<dd>Started the library and contributed the theoretical and optimal
|
||
|
|
CRC computation class templates and the CRC computing function
|
||
|
|
template. Contributed <cite><a
|
||
|
|
href="test/crc_test.cpp">crc_test.cpp</a></cite> and <cite><a
|
||
|
|
href="crc_example.cpp">crc_example.cpp</a></cite>.
|
||
|
|
|
||
|
|
<dt>Ross N. Williams
|
||
|
|
<dd>Wrote <cite><a href="http://www.ross.net/crc/crcpaper.html">A
|
||
|
|
Painless Guide to CRC Error Detection Algorithms</a></cite>, a
|
||
|
|
definitive source of CRC information.
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<h3><a name="acknowledgements">Acknowledgements</a></h3>
|
||
|
|
|
||
|
|
<p>For giving advice on compiler/C++ compliance, implementation,
|
||
|
|
interface, algorithms, and bug reports:</p>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>Darin Adler</li>
|
||
|
|
<li>Beman Dawes</li>
|
||
|
|
<li>Doug Gregor</li>
|
||
|
|
<li>John Maddock</li>
|
||
|
|
<li>Joe Mariadassou</li>
|
||
|
|
<li>Jens Maurer</li>
|
||
|
|
<li>Vladimir Prus</li>
|
||
|
|
<li>Joel Young</li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<h3><a name="history">History</a></h3>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt>15 Jun 2003, Daryle Walker
|
||
|
|
<dd>Added example program.
|
||
|
|
|
||
|
|
<dt>14 May 2001, Daryle Walker
|
||
|
|
<dd>Initial version.
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
|
||
|
|
<p>Revised: 15 June 2003</p>
|
||
|
|
|
||
|
|
<p>Copyright 2001, 2003 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>
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|