Crc.cxx File Reference

#include <stdint.h>
#include "utils/Crc.hxx"
#include "utils/macros.h"

Go to the source code of this file.

Functions
uint8_t	reverse (uint8_t data)
	Reverses the bits of a byte.
void	crc_16_ibm_add (uint16_t &state, uint8_t data)
	Appends a byte to a CRC16 state machine.
void	crc_16_ibm_add_basic (uint16_t &state, uint8_t data)
	Bitwise implementation of the crc16 ibm add.
uint16_t	crc_16_ibm_finish (uint16_t state)
	Finalizes the state machine of a CRC16-IBM calculator.
uint16_t	crc_16_ibm (const void *data, size_t length)
	Computes the 16-bit CRC value over data using the CRC16-ANSI (aka CRC16-IBM) settings.
void	crc3_crc16_ibm (const void *data, size_t length_bytes, uint16_t *checksum)
	Computes the triple-CRC value over a chunk of data.

Variables
static const uint16_t	crc_16_ibm_init_value = 0x0000
	Initialization value for the CRC-16-IBM calculator.
static const uint16_t	crc_16_ibm_poly = 0xA001
	Polynomial for the CRC-16-IBM calculator.
static const uint16_t	CRC16_IBM_HI [16]
	Translation table for crc16-ibm, high nibble.
static const uint16_t	CRC16_IBM_LO [16]
	Translation table for crc16-ibm, low nibble.

Detailed Description

Copyright

Copyright (c) 2014, Balazs Racz All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Helper functions for computing checksums.

Author

Balazs Racz

Date

16 Dec 2014

Definition in file Crc.cxx.

Function Documentation

crc3_crc16_ibm()

void crc3_crc16_ibm	(	const void *	data,
		size_t	length_bytes,
		uint16_t *	checksum
	)

Computes the triple-CRC value over a chunk of data.

checksum is an array of 3 halfwords. The first halfword will get the CRC of the data array, the second halfword the CRC of all odd bytes (starting with the first byte), the third halfword will get the CRC of all even bytes.

This routine is helpful, because a similar routine is part of the TIVA microcontroller ROM, thus needs no implementation on an actual part. It is important to note that the TIVA version takes the length in 4-byte words and allows only using data length divisible by 4.

Parameters

data	what to compute the checksum over
length_bytes	how long data is
checksum	is the output buffer where to store the 48-bit checksum.

Definition at line 167 of file Crc.cxx.

crc_16_ibm()

uint16_t crc_16_ibm	(	const void *	data,
		size_t	length_bytes
	)

Computes the 16-bit CRC value over data using the CRC16-ANSI (aka CRC16-IBM) settings.

This involves zero init value, zero terminating value, reversed polynomial 0xA001, reversing input bits and reversing output bits. The example CRC value of "123456789" is 0xbb3d.

Parameters

data	what to compute the checksum over
length_bytes	how long data is

Returns

the CRC-16-IBM value of the checksummed data.

Definition at line 156 of file Crc.cxx.

crc_16_ibm_add()

void crc_16_ibm_add ( uint16_t &  state, uint8_t  data  )

inline

Appends a byte to a CRC16 state machine.

Parameters

state	the state machine of the CRC computer.
data	next byte to add.

Definition at line 116 of file Crc.cxx.

crc_16_ibm_add_basic()

void crc_16_ibm_add_basic	(	uint16_t &	state,
		uint8_t	data
	)

Bitwise implementation of the crc16 ibm add.

Definition at line 124 of file Crc.cxx.

crc_16_ibm_finish()

uint16_t crc_16_ibm_finish ( uint16_t  state )

inline

Finalizes the state machine of a CRC16-IBM calculator.

Parameters

state

internal state of the machine.

Returns

the CRC-16-IBM value of the byte sequence added to the state machine during its lifetime.

Definition at line 147 of file Crc.cxx.

reverse()

uint8_t reverse

(

uint8_t

data

)

Reverses the bits of a byte.

Parameters

data	input byte

Returns

the input bits reversed (bit 0 exchanged with bit 7 et al.)

Definition at line 51 of file Crc.cxx.

Variable Documentation

CRC16_IBM_HI

const uint16_t CRC16_IBM_HI[16]

static

Initial value:

=
{
    0x0000, 0xcc01, 0xd801, 0x1400, 0xf001, 0x3c00, 0x2800, 0xe401,
    0xa001, 0x6c00, 0x7800, 0xb401, 0x5000, 0x9c01, 0x8801, 0x4400,
}

Translation table for crc16-ibm, high nibble.

Definition at line 98 of file Crc.cxx.

CRC16_IBM_LO

const uint16_t CRC16_IBM_LO[16]

static

Initial value:

=
{
    0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0, 0x0280, 0xc241,
    0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,
}

Translation table for crc16-ibm, low nibble.

Definition at line 104 of file Crc.cxx.

crc_16_ibm_init_value

const uint16_t crc_16_ibm_init_value = 0x0000

static

Initialization value for the CRC-16-IBM calculator.

Definition at line 41 of file Crc.cxx.

crc_16_ibm_poly

const uint16_t crc_16_ibm_poly = 0xA001

static

Polynomial for the CRC-16-IBM calculator.

Definition at line 43 of file Crc.cxx.