# Chksum : Checksum calculation tools

This module provides common checksum calculation functions, including internet chksum, various CRC algorithms, etc.

User can use the following code to import the Chksum module.

var Chksum = require('chksum');

# Support

The following shows Chksum module APIs available for each permissions.

# Chksum Class

# new Chksum()

• Returns: {Object} Chksum object.

Create a chksum object for computing internet chksum and nmea chksum.

# Example

var chksum = new Chksum();

# new Chksum(crcType[, lsb])

• crcType {Integer} CRC algorithm type.
• lsb {Boolean} Whether store the result as LSB. default: MSB.
• Returns: {Object} Chksum object.

crcType can be the following value:

• Chksum.CRC8
• Chksum.CRC16
• Chksum.CRC16_CCITT_1DOF
• Chksum.CRC16_CCITT_FFFF
• Chksum.CRC16_DNP
• Chksum.CRC16_KERMIT
• Chksum.CRC16_MODBUS
• Chksum.CRC16_SICK
• Chksum.CRC16_XMODEM
• Chksum.CRC32
• Chksum.CRC64_ECMA
• Chksum.CRC64_WE

Create a chksum object for calculating CRC.

# Example

var chksum = new Chksum(Chksum.CRC16);

# Chksum Object

# chksum.crc(outBuf, outOffset, string)

• outBuf {Buffer} Output buffer.
• outOffset {Integer} Output buffer position.
• string {String} Input string.
• Returns: {Integer} Chksum bytes length.

Calculate the CRC chksum of a string and store the result in the specified location.

# Example

var chksum = new Chksum(Chksum.CRC16);
var buffer = new Buffer(2);

chksum.crc(buffer, 0, 'Test CRC');

# chksum.crc(outBuf, outOffset, buffer[, offset[, length]])

• outBuf {Buffer} Output buffer.
• outOffset {Integer} Output buffer position.
• buffer {Buffer} Input buffer.
• offset {Integer} Input buffer offset. default: 0.
• length {Integer} Input data length. default:buffer.length.
• Returns: {Integer} Chksum bytes length.

Calculate the CRC chksum of a buffer and store the result in the specified location.

# Example

var chksum = new Chksum(Chksum.CRC16);
var buffer = new Buffer(10);

buffer.fromString('abcdefgh');
chksum.crc(buffer, 8, buffer, 0, 8);

# chksum.nmea(outBuf, outOffset, string)

• outBuf {Buffer} Output buffer.
• outOffset {Integer} Output buffer position.
• string {String} Input string.
• Returns: {Integer} Chksum bytes length. If success returns 3.

Calculate the NMEA chksum of a string and store the result in the specified location.

var chksum = new Chksum();
var buffer = new Buffer(3);

chksum.nmea(buffer, 0, 'Test NMEA');

# chksum.inet(outBuf, outOffset, string)

• outBuf {Buffer} Output buffer.
• outOffset {Integer} Output buffer position.
• string {String} Input string.
• Returns: {Integer} Chksum bytes length. If success returns 2.

Calculate the internet chksum of a string and store the result in the specified location.

var chksum = new Chksum();
var buffer = new Buffer(2);

chksum.inet(buffer, 0, 'Test INET');

# chksum.inet(outBuf, outOffset, buffer[, offset[, length]])

• outBuf {Buffer} Output buffer.
• outOffset {Integer} Output buffer position.
• buffer {Buffer} Input buffer.
• offset {Integer} Input buffer offset. default: 0.
• length {Integer} Input data length. default:buffer.length.
• Returns: {Integer} Chksum bytes length. If success returns 2.

Calculate the internet chksum of a buffer and store the result in the specified location.

# Example

var chksum = new Chksum();
var buffer = new Buffer(10);

buffer.fromString('abcdefgh');
chksum.inet(buffer, 8, buffer, 0, 8);