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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// 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.
package crc32
import (
"errors"
"hash"
"sync"
"sync/atomic"
)
// The size of a CRC-32 checksum in bytes.
const Size = 4
// Predefined polynomials.
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
)
// Table is a 256-word table representing the polynomial for efficient processing.
type Table [256]uint32
// This file makes use of functions implemented in architecture-specific files.
// The interface that they implement is as follows:
//
// // archAvailableIEEE reports whether an architecture-specific CRC32-IEEE
// // algorithm is available.
// archAvailableIEEE() bool
//
// // archInitIEEE initializes the architecture-specific CRC3-IEEE algorithm.
// // It can only be called if archAvailableIEEE() returns true.
// archInitIEEE()
//
// // archUpdateIEEE updates the given CRC32-IEEE. It can only be called if
// // archInitIEEE() was previously called.
// archUpdateIEEE(crc uint32, p []byte) uint32
//
// // archAvailableCastagnoli reports whether an architecture-specific
// // CRC32-C algorithm is available.
// archAvailableCastagnoli() bool
//
// // archInitCastagnoli initializes the architecture-specific CRC32-C
// // algorithm. It can only be called if archAvailableCastagnoli() returns
// // true.
// archInitCastagnoli()
//
// // archUpdateCastagnoli updates the given CRC32-C. It can only be called
// // if archInitCastagnoli() was previously called.
// archUpdateCastagnoli(crc uint32, p []byte) uint32
// castagnoliTable points to a lazily initialized Table for the Castagnoli
// polynomial. MakeTable will always return this value when asked to make a
// Castagnoli table so we can compare against it to find when the caller is
// using this polynomial.
var castagnoliTable *Table
var castagnoliTable8 *slicing8Table
var updateCastagnoli func(crc uint32, p []byte) uint32
var castagnoliOnce sync.Once
var haveCastagnoli atomic.Bool
func castagnoliInit() {
castagnoliTable = simpleMakeTable(Castagnoli)
if archAvailableCastagnoli() {
archInitCastagnoli()
updateCastagnoli = archUpdateCastagnoli
} else {
// Initialize the slicing-by-8 table.
castagnoliTable8 = slicingMakeTable(Castagnoli)
updateCastagnoli = func(crc uint32, p []byte) uint32 {
return slicingUpdate(crc, castagnoliTable8, p)
}
}
haveCastagnoli.Store(true)
}
// IEEETable is the table for the IEEE polynomial.
var IEEETable = simpleMakeTable(IEEE)
// ieeeTable8 is the slicing8Table for IEEE
var ieeeTable8 *slicing8Table
var updateIEEE func(crc uint32, p []byte) uint32
var ieeeOnce sync.Once
func ieeeInit() {
if archAvailableIEEE() {
archInitIEEE()
updateIEEE = archUpdateIEEE
} else {
// Initialize the slicing-by-8 table.
ieeeTable8 = slicingMakeTable(IEEE)
updateIEEE = func(crc uint32, p []byte) uint32 {
return slicingUpdate(crc, ieeeTable8, p)
}
}
}
// MakeTable returns a Table constructed from the specified polynomial.
// The contents of this Table must not be modified.
func MakeTable(poly uint32) *Table {
switch poly {
case IEEE:
ieeeOnce.Do(ieeeInit)
return IEEETable
case Castagnoli:
castagnoliOnce.Do(castagnoliInit)
return castagnoliTable
default:
return simpleMakeTable(poly)
}
}
// digest represents the partial evaluation of a checksum.
type digest struct {
crc uint32
tab *Table
}
// 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 New(tab *Table) hash.Hash32 {
if tab == IEEETable {
ieeeOnce.Do(ieeeInit)
}
return &digest{0, tab}
}
// 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 NewIEEE() hash.Hash32 { return New(IEEETable) }
func (d *digest) Size() int { return Size }
func (d *digest) BlockSize() int { return 1 }
func (d *digest) Reset() { d.crc = 0 }
const (
magic = "crc\x01"
marshaledSize = len(magic) + 4 + 4
)
func (d *digest) MarshalBinary() ([]byte, error) {
b := make([]byte, 0, marshaledSize)
b = append(b, magic...)
b = appendUint32(b, tableSum(d.tab))
b = appendUint32(b, d.crc)
return b, nil
}
func (d *digest) UnmarshalBinary(b []byte) error {
if len(b) < len(magic) || string(b[:len(magic)]) != magic {
return errors.New("hash/crc32: invalid hash state identifier")
}
if len(b) != marshaledSize {
return errors.New("hash/crc32: invalid hash state size")
}
if tableSum(d.tab) != readUint32(b[4:]) {
return errors.New("hash/crc32: tables do not match")
}
d.crc = readUint32(b[8:])
return nil
}
func appendUint32(b []byte, x uint32) []byte {
a := [4]byte{
byte(x >> 24),
byte(x >> 16),
byte(x >> 8),
byte(x),
}
return append(b, a[:]...)
}
func readUint32(b []byte) uint32 {
_ = b[3]
return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
}
func update(crc uint32, tab *Table, p []byte, checkInitIEEE bool) uint32 {
switch {
case haveCastagnoli.Load() && tab == castagnoliTable:
return updateCastagnoli(crc, p)
case tab == IEEETable:
if checkInitIEEE {
ieeeOnce.Do(ieeeInit)
}
return updateIEEE(crc, p)
default:
return simpleUpdate(crc, tab, p)
}
}
// Update returns the result of adding the bytes in p to the crc.
func Update(crc uint32, tab *Table, p []byte) uint32 {
// Unfortunately, because IEEETable is exported, IEEE may be used without a
// call to MakeTable. We have to make sure it gets initialized in that case.
return update(crc, tab, p, true)
}
func (d *digest) Write(p []byte) (n int, err error) {
// We only create digest objects through New() which takes care of
// initialization in this case.
d.crc = update(d.crc, d.tab, p, false)
return len(p), nil
}
func (d *digest) Sum32() uint32 { return d.crc }
func (d *digest) Sum(in []byte) []byte {
s := d.Sum32()
return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
}
// Checksum returns the CRC-32 checksum of data
// using the polynomial represented by the Table.
func Checksum(data []byte, tab *Table) uint32 { return Update(0, tab, data) }
// ChecksumIEEE returns the CRC-32 checksum of data
// using the IEEE polynomial.
func ChecksumIEEE(data []byte) uint32 {
ieeeOnce.Do(ieeeInit)
return updateIEEE(0, data)
}
// tableSum returns the IEEE checksum of table t.
func tableSum(t *Table) uint32 {
var a [1024]byte
b := a[:0]
if t != nil {
for _, x := range t {
b = appendUint32(b, x)
}
}
return ChecksumIEEE(b)
}
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