pabigot::crc::Tabler< CRC > Class Template Reference

Class encapsulating everything necessary for table-driven CRC calculations. More...

#include </mnt/devel/pabigot-cxx/include/pabigot/crc.hpp>

Inheritance diagram for pabigot::crc::Tabler< CRC >:

Data Structures
struct	params
	Rocksoft^TM model parameters for the checksum algorithm supported by this type. More...

Public Types
using	crc_type = CRC
	The underlying crc type.
using	table_type = std::array< least_type, 256 >
	How the CRC table elements are stored.

Public Member Functions
uint8_t *	store (least_type crc, uint8_t *bp) const
	Store a finalized CRC into a buffer in a way that enables crc::residue(). More...
constexpr fast_type	append (uint8_t octet, fast_type crc=init) const
	Table-driven update of a CRC given a data octet. More...
template<typename InputIterator >
constexpr fast_type	append (InputIterator first, InputIterator last, fast_type crc=init) const
	Table-driven calculation of a CRC from a sequence of octet values. More...
constexpr least_type	finalize (fast_type crc) const
	Perform necessary post-processing to get the final checksum. More...

Data Fields
const table_type	table
	The CRC table, indexed by unreflected input octet.

Static Public Attributes
static constexpr size_t	size = CRC::size
	The number of bytes required to store a CRC value of #width bits.
static constexpr fast_type	init = make_init()
	The CRC initial value in the form required for table calculations.
static constexpr least_type	residue = CRC::residue()
	The value expected when calculating the finalized CRC over an aggregate of a message and its store()d checksum.

Detailed Description

template<typename CRC>
class pabigot::crc::Tabler< CRC >

Class encapsulating everything necessary for table-driven CRC calculations.

The table is an instance member; everything else is a constexpr class static member. Construct these as global objects at compile-time with definitions like:

constexpr auto crc = pabigot::crc::crc<32, 0x04c11db7, true, true, -1, -1>::instantiate_tabler();

Use them like:

uint8_t* cp = prepare_message(buf);
auto pre = crc.append(buf, cp);
const uint8_t* ep = crc.store(crc.finalize(pre), cp);
transmit(buf, ep);

On reception:

auto len = receive(buf);
if (crc.residue != crc.finalize(crc.append(buf, buf + len))) {
  // error in aggregate message
}

Member Function Documentation

append() [1/2]

template<typename CRC >

template<typename InputIterator >

constexpr fast_type pabigot::crc::Tabler< CRC >::append ( InputIterator  first, InputIterator  last, fast_type  crc = init  ) const

inlineconstexpr

Table-driven calculation of a CRC from a sequence of octet values.

Template Parameters

InputIterator

iterator over inputs. InputIterator::value_type must be convertible to an unsigned 8-bit value without changing the value content.

Parameters

first	beginning of the range over which CRCs will be calculated.
last	beginning of the range over which CRCs will be calculated.
crc	the CRC value calculated over all previous message bits. Start with init, which is the defaulted value.

Returns

the unreflected CRC value over all message bits through this invocation.

See also

finalize()

append() [2/2]

template<typename CRC >

constexpr fast_type pabigot::crc::Tabler< CRC >::append ( uint8_t  octet, fast_type  crc = init  ) const

inlineconstexpr

Table-driven update of a CRC given a data octet.

Parameters

octet	the next octet of message bits.
crc	the CRC value calculated over all previous message bits. Start with init, which is the defaulted value.

Returns

the unreflected CRC value over all message bits through this invocation.

See also

finalize()

finalize()

template<typename CRC >

constexpr least_type pabigot::crc::Tabler< CRC >::finalize ( fast_type  crc ) const

inlineconstexpr

Perform necessary post-processing to get the final checksum.

Parameters

crc	an unreflected unmodified CRC over input bits.

Returns

the reflected modified CRC.

store()

template<typename CRC >

uint8_t* pabigot::crc::Tabler< CRC >::store ( least_type  crc, uint8_t *  bp  ) const

inline

Store a finalized CRC into a buffer in a way that enables crc::residue().

Parameters

crc	the finalized CRC of a message.
bp	pointer to space of size bytes immediately following the message, into which the CRC can be stored.

Returns

pointer into the region identified by bp immediately following the stored CRC.

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The documentation for this class was generated from the following file:

• /mnt/devel/pabigot-cxx/include/pabigot/crc.hpp