version: 1.10

package crc32

import "hash/crc32"

Overview

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

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

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

Index

Examples

Package files

crc32.go crc32_amd64.go crc32_generic.go

Constants

  1. const (
  2.     // IEEE is by far and away the most common CRC-32 polynomial.
  3.     // Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...
  4.     IEEE = 0xedb88320
  5.  
  6.     // Castagnoli's polynomial, used in iSCSI.
  7.     // Has better error detection characteristics than IEEE.
  8.     // http://dx.doi.org/10.1109/26.231911
  9.     Castagnoli = 0x82f63b78
  10.  
  11.     // Koopman's polynomial.
  12.     // Also has better error detection characteristics than IEEE.
  13.     // http://dx.doi.org/10.1109/DSN.2002.1028931
  14.     Koopman = 0xeb31d82e
  15. )

Predefined polynomials.

  1. const Size = 4

The size of a CRC-32 checksum in bytes.

Variables

  1. var IEEETable = simpleMakeTable(IEEE)

IEEETable is the table for the IEEE polynomial.

func Checksum

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

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

func ChecksumIEEE

  1. func ChecksumIEEE(data []byte) uint32

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

func New

  1. 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

  1. 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

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

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

type Table

  1. type Table [256]uint32

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

func MakeTable

  1. func MakeTable(poly uint32) *Table

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


Example:

  1. // In this package, the CRC polynomial is represented in reversed notation,
  2. // or LSB-first representation.
  3. //
  4. // LSB-first representation is a hexadecimal number with n bits, in which the
  5. // most significant bit represents the coefficient of x⁰ and the least significant
  6. // bit represents the coefficient of xⁿ⁻¹ (the coefficient for xⁿ is implicit).
  7. //
  8. // For example, CRC32-Q, as defined by the following polynomial,
  9. //    x³²+ x³¹+ x²⁴+ x²²+ x¹⁶+ x¹⁴+ x⁸+ x⁷+ x⁵+ x³+ x¹+ x⁰
  10. // has the reversed notation 0b11010101100000101000001010000001, so the value
  11. // that should be passed to MakeTable is 0xD5828281.
  12. crc32q := crc32.MakeTable(0xD5828281)
  13. fmt.Printf("%08x\n", crc32.Checksum([]byte("Hello world"), crc32q))
  14. // Output:
  15. // 2964d064