crc16

Documentation

Overview

Package crc16 implements the 16-bit cyclic redundancy check, or CRC-16, checksum. See http://en.wikipedia.org/wiki/Cyclic_redundancy_check for information.

Index

• Constants
• Variables
• func Checksum(c *Conf, data []byte) uint16
• func Update(crc uint16, tab *Table, p []byte) uint16
• func UpdateNBR(crc uint16, tab *Table, p []byte) uint16
• type Conf
• type Hash16
  • func New(c *Conf) Hash16
• type Table
  • func MakeTable(poly uint16) *Table
  • func MakeTableNBR(poly uint16) *Table

Constants

const Size = 2

The size of a CRC-16 checksum in bytes.

Variables

var (
	// Typical CRC-16 configurations. Mostly used are the CCITT
	// (0x1021) and the IBM/ANSI (0x8005) polynomials, either
	// bit-reversed or not. For more configurations see:
	// http://reveng.sourceforge.net/crc-catalogue/
	X25 = &Conf{
		Poly: 0x1021, BitRev: true,
		IniVal: 0xffff, FinVal: 0xffff,
		BigEnd: false,
	}
	PPP    = X25
	Modbus = &Conf{
		Poly: 0x8005, BitRev: true,
		IniVal: 0xffff, FinVal: 0x0,
		BigEnd: false,
	}
	XModem = &Conf{
		Poly: 0x1021, BitRev: false,
		IniVal: 0x0000, FinVal: 0x0,
		BigEnd: true,
	}
	Kermit = &Conf{
		Poly: 0x1021, BitRev: true,
		IniVal: 0x0, FinVal: 0x0,
		BigEnd: false,
	}
)

Functions

func Checksum

func Checksum(c *Conf, data []byte) uint16

Checksum returns the CRC-16 checksum of data using the configuration c.

func Update

func Update(crc uint16, tab *Table, p []byte) uint16

Update returns the CRC-16 checksum of p using the polynomial table tab constructed by MakeTable (bit-reversed order). The resulting CRC is in bit-reversed order (bit-15 corresponds to the X^0 term). Argument crc is the initial value of the CRC register.

func UpdateNBR

func UpdateNBR(crc uint16, tab *Table, p []byte) uint16

UpdateNBR returns the CRC-16 checksum of p using the polynomial table tab constructed by MakeTableNBR (non-bit-reversed order). The resulting CRC is in non-bit-reversed order (bit-0 corresponds to the X^0 term). Argument CRC is the initial value of the CRC register.

Types

type Conf

type Conf struct {
	Poly   uint16 // Polynomial to use.
	BitRev bool   // Bit reversed CRC (bit-15 is X^0)?
	IniVal uint16 // Initial value of CRC register.
	FinVal uint16 // XOR CRC with this at the end.
	BigEnd bool   // Emit *bytes* most significant first?
	// contains filtered or unexported fields
}

Conf is a CRC configuration. It is passed to functions New and Checksum and specifies the parameters of the calculated checksum. The first time New or Checksum are called with a configuration structure c, they calculate the polynomial table for this configuration; subsequent calls with the same c use the table already calculated. A few commonly used configurations are defined as global variables (X25, PPP, Modbus, etc.)

type Hash16

type Hash16 interface {
	hash.Hash
	Sum16() uint16
}

Hash16 is the common interface implemented by all 16-bit hash functions.

func New

func New(c *Conf) Hash16

New creates a new hash.Hash16 computing the CRC-16 checksum using the configuration c.

type Table

type Table [256]uint16

Table is a 256-word table representing the polynomial for efficient processing.

func MakeTable

func MakeTable(poly uint16) *Table

MakeTable returns the Table constructed from the specified polynomial. The table is calcuated in bit-reversed order (bit-15 corresponds to the X^0 term). Argument poly must be given bit-reversed (e.g. 0xA001 for the 0x8005 polynomial).

func MakeTableNBR

func MakeTableNBR(poly uint16) *Table

MakeTableNBR returns the Table constructed from the specified polynomial. The table is calculated in non-bit-reversed order (bit-0 corresponds to the X^0 term).