crc32

Documentation

Overview

Package crc32 implements the 32-bit cyclic redundancy check, or CRC-32, checksum. See https://en.wikipedia.org/wiki/Cyclic_redundancy_check for information.

Polynomials are represented in LSB-first form also known as reversed representation.

See https://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks#Reversed_representations_and_reciprocal_polynomials for information.

Index

• Constants
• Variables
• func Checksum(data []byte, tab *Table) uint32
• func ChecksumIEEE(data []byte) uint32
• func New(tab *Table) hash.Hash32
• func NewIEEE() hash.Hash32
• func Update(crc uint32, tab *Table, p []byte) uint32
• type Table
  • func MakeTable(poly uint32) *Table

Examples

• MakeTable

Constants

const (
	// IEEE is by far and away the most common CRC-32 polynomial.
	// Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...
	IEEE = 0xedb88320

	// Castagnoli's polynomial, used in iSCSI.
	// Has better error detection characteristics than IEEE.
	// https://dx.doi.org/10.1109/26.231911
	Castagnoli = 0x82f63b78

	// Koopman's polynomial.
	// Also has better error detection characteristics than IEEE.
	// https://dx.doi.org/10.1109/DSN.2002.1028931
	Koopman = 0xeb31d82e
)

Predefined polynomials.

const Size = 4

The size of a CRC-32 checksum in bytes.

Variables

var IEEETable = simpleMakeTable(IEEE)

IEEETable is the table for the IEEE polynomial.

Functions

func Checksum

func Checksum(data []byte, tab *Table) uint32

Checksum returns the CRC-32 checksum of data using the polynomial represented by the Table.

func ChecksumIEEE

func ChecksumIEEE(data []byte) uint32

ChecksumIEEE returns the CRC-32 checksum of data using the IEEE polynomial.

func New

func New(tab *Table) hash.Hash32

New creates a new hash.Hash32 computing the CRC-32 checksum using the polynomial represented by the Table. Its Sum method will lay the value out in big-endian byte order. The returned Hash32 also implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to marshal and unmarshal the internal state of the hash.

func NewIEEE

func NewIEEE() hash.Hash32

NewIEEE creates a new hash.Hash32 computing the CRC-32 checksum using the IEEE polynomial. Its Sum method will lay the value out in big-endian byte order. The returned Hash32 also implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to marshal and unmarshal the internal state of the hash.

func Update

func Update(crc uint32, tab *Table, p []byte) uint32

Update returns the result of adding the bytes in p to the crc.

Types

type Table

type Table [256]uint32

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

func MakeTable

func MakeTable(poly uint32) *Table

MakeTable returns a Table constructed from the specified polynomial. The contents of this Table must not be modified.

Example

package main

import (
	"fmt"
	"hash/crc32"
)

func main() {
	// In this package, the CRC polynomial is represented in reversed notation,
	// or LSB-first representation.
	//
	// LSB-first representation is a hexadecimal number with n bits, in which the
	// most significant bit represents the coefficient of x⁰ and the least significant
	// bit represents the coefficient of xⁿ⁻¹ (the coefficient for xⁿ is implicit).
	//
	// For example, CRC32-Q, as defined by the following polynomial,
	//	x³²+ x³¹+ x²⁴+ x²²+ x¹⁶+ x¹⁴+ x⁸+ x⁷+ x⁵+ x³+ x¹+ x⁰
	// has the reversed notation 0b11010101100000101000001010000001, so the value
	// that should be passed to MakeTable is 0xD5828281.
	crc32q := crc32.MakeTable(0xD5828281)
	fmt.Printf("%08x\n", crc32.Checksum([]byte("Hello world"), crc32q))
}

Output:

2964d064