CRC calculation using Rocksoft^tm Model characteristics. More...

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

Inheritance diagram for pabigot::crc::crc< W, Poly, Rin, Rout, Init, XorOut >:

Public Types
using	tabler_type = Tabler< this_type >
	The Tabler associated with this CRC type.

using	fast_type = typename support_traits::fast_type
	A fast native unsigned integral type capable of holding width-bit CRC values. More...

using	least_type = typename support_traits::least_type
	A small native unsigned integral type capable of holding width-bit CRC values. More...

Public Types inherited from pabigot::crc::details::base_crc< W, Rin >
using	uint_traits = typename support_traits::uint_traits

using	fast_type = typename support_traits::fast_type
	A fast native unsigned integral type capable of holding width-bit CRC values. More...

using	least_type = typename support_traits::least_type
	A small native unsigned integral type capable of holding width-bit CRC values. More...

Static Public Member Functions
static constexpr least_type	residue ()
	Value expected for `CRC(x \|\| XE(CRC(x)))`. More...

template<typename InputIterator >
static constexpr fast_type	append (InputIterator first, InputIterator last, const fast_type &crc=init)
	Augment a checksum with additional data. More...

static constexpr least_type	lookup_for_byte (std::uint_fast8_t byte)
	Delegate to super_::lookup_for_byte.

static constexpr least_type	finalize (fast_type crc)
	Calculate the final CRC value for a sequence. More...

static constexpr tabler_type	instantiate_tabler ()
	Construct an object that does table-driven CRC calculations for this algorithm.

static constexpr uint8_t *	store (fast_type crc, uint8_t *bp)
	Store a finalized CRC into a buffer in a way that enables crc::residue(). More...

Static Public Member Functions inherited from pabigot::crc::details::base_crc< W, Rin >
static constexpr fast_type	reflect (const fast_type &v)
	Delegate to support_traits::reflect.

static constexpr uint8_t *	store (fast_type crc, uint8_t *bp)
	Store a finalized CRC into a buffer in a way that enables crc::residue(). More...

Static Public Attributes
static constexpr bool	refout = Rout
	`true` iff the output CRC is to be reflected.

static constexpr fast_type	poly = super_::mask & Poly
	The CRC polynomial in normal form (all bits except bit width which is known to be 1 are provided).

static constexpr least_type	init = super_::mask & Init
	The initial value of the CRC register before any message bits have been processed.

static constexpr least_type	xorout = super_::mask & XorOut
	A value subtracted (xor'd) from the calculated result prior to returning it.

Static Public Attributes inherited from pabigot::crc::details::base_crc< W, Rin >
static constexpr unsigned int	width = W
	The width of the CRC in bits.

static constexpr unsigned int	size = (7 + width) / 8
	The width of the CRC in bytes.

static constexpr fast_type	mask = support_traits::mask
	The mask that discards bits of a fast_type that would be outside the width limit.

static constexpr bool	refin = Rin
	`true` iff the input message bit stream is reflected. More...

Protected Types
using	support_traits = details::uint_support< width >
	Traits class providing native integral types and parameter-independent values supporting width-bit operations.

Protected Types inherited from pabigot::crc::details::base_crc< W, Rin >
using	support_traits = details::uint_support< width >
	Traits class providing native integral types and parameter-independent values supporting width-bit operations.

Additional Inherited Members
Static Protected Member Functions inherited from pabigot::crc::details::base_crc< W, Rin >
static constexpr least_type	lookup_for_byte (const fast_type &poly, std::uint_fast8_t byte)
	Calculate a single lookup table entry using the given polynomial. More...

static constexpr fast_type	crc_apply (const fast_type &poly, const fast_type &crc, fast_type msg, unsigned int n)
	Apply message bits into a CRC. More...

Detailed Description

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>
class pabigot::crc::crc< W, Poly, Rin, Rout, Init, XorOut >

CRC calculation using Rocksoft^tm Model characteristics.

Template Parameters

W	the width of the CRC in bits.
Poly	the CRC polynomial in normal form.
Rin	whether the input bit stream is reflected.
Rout	whether the output bit stream is reflected.
Init	the initial value of the CRC register before any bits have been processed. A value of `-1` may be used to start with all bits set. XorOut the value xorout subtracted from the calculated result prior to returning it. A value of `-1` may be used to bitwise invert the value.

See also: http://www.ross.net/crc/download/crc_v3.txt; http://reveng.sourceforge.net/crc-catalogue/; http://users.ece.cmu.edu/~koopman/crc/index.html; https://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks especially the Koopman references

Member Typedef Documentation

◆ fast_type

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>

using pabigot::crc::details::base_crc< W, Rin >::fast_type = typename support_traits::fast_type

A fast native unsigned integral type capable of holding width-bit CRC values.

Warning: This value may have more octets or bits than are required to store the CRC.

◆ least_type

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>

using pabigot::crc::details::base_crc< W, Rin >::least_type = typename support_traits::least_type

A small native unsigned integral type capable of holding width-bit CRC values.

Warning: This value may have more octets or bits than are required to store the CRC.

Member Function Documentation

◆ append()

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>

template<typename InputIterator >

static constexpr fast_type pabigot::crc::crc< W, Poly, Rin, Rout, Init, XorOut >::append	(	InputIterator	first,
		InputIterator	last,
		const fast_type &	crc = `init`
	)

inlinestaticconstexpr

Augment a checksum with additional data.

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. This may be passed as crc to process more message content.

See also: finalize()

◆ finalize()

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>

static constexpr least_type pabigot::crc::crc< W, Poly, Rin, Rout, Init, XorOut >::finalize ( fast_type crc )

inlinestaticconstexpr

Calculate the final CRC value for a sequence.

refout and xorout are applied to the final register value and the result returned.

Note: A common operation on CRCs is to store them into a buffer for transfer to another system, particularly to enable use of residue(). Be aware that if width is not a power of 2 then least_type is likely to have padding bits in it, for which a basic byte-swap for endianness will produce anomalous results. See store() for a partial solution.

Parameters

crc	the CRC resulting after all message bits have been calculated.

Returns: the CRC of the message in smallest type capable of holding it.

◆ residue()

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>

static constexpr least_type pabigot::crc::crc< W, Poly, Rin, Rout, Init, XorOut >::residue ( )

inlinestaticconstexpr

Value expected for CRC(x || XE(CRC(x))).

When the checksum of the message is stored at the end of the message a receiver can calculate the finalized checksum of the message plus the stored checksum. This value will be equal to the residue() if no errors are discovered.

Note: The residues produced by this function may not match those specified by the reveng catalog because the classic check algorithm used for residues does not apply crc::xorout to the final value. See, for example, this code for the classic CRC-32 algorithm. The value here is correct when compared with a finalized checksum.

Warning: This library does not properly handle residue calculation for messages that are not an integral number of bytes, or CRCs with a width that is not a multiple of 8 bits.

◆ store()

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>

static constexpr uint8_t* pabigot::crc::details::base_crc< W, Rin >::store

inlinestaticconstexpr

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

Warning: If the CRC width is not a multiple of 8 the stored value will not be correct, as this namespace provides no API to operate on messages that are not an integral number of octets.

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.

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

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

Public Types

Static Public Member Functions

Static Public Attributes

Protected Types

Additional Inherited Members

Detailed Description

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0> class pabigot::crc::crc< W, Poly, Rin, Rout, Init, XorOut >

Member Typedef Documentation

◆ fast_type

◆ least_type

Member Function Documentation

◆ append()

◆ finalize()

◆ residue()

◆ store()

template<unsigned int W, uintmax_t Poly, bool Rin = false, bool Rout = false, uintmax_t Init = 0, uintmax_t XorOut = 0>
class pabigot::crc::crc< W, Poly, Rin, Rout, Init, XorOut >