mirror of
https://github.com/go-gitea/gitea.git
synced 2024-12-05 09:49:37 +08:00
208 lines
6.2 KiB
Go
208 lines
6.2 KiB
Go
|
// 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 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.
|
||
|
package crc32
|
||
|
|
||
|
import (
|
||
|
"hash"
|
||
|
"sync"
|
||
|
)
|
||
|
|
||
|
// 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.
|
||
|
// http://dx.doi.org/10.1109/26.231911
|
||
|
Castagnoli = 0x82f63b78
|
||
|
|
||
|
// Koopman's polynomial.
|
||
|
// Also has better error detection characteristics than IEEE.
|
||
|
// http://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 castagnoliArchImpl bool
|
||
|
var updateCastagnoli func(crc uint32, p []byte) uint32
|
||
|
var castagnoliOnce sync.Once
|
||
|
|
||
|
func castagnoliInit() {
|
||
|
castagnoliTable = simpleMakeTable(Castagnoli)
|
||
|
castagnoliArchImpl = archAvailableCastagnoli()
|
||
|
|
||
|
if castagnoliArchImpl {
|
||
|
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)
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// IEEETable is the table for the IEEE polynomial.
|
||
|
var IEEETable = simpleMakeTable(IEEE)
|
||
|
|
||
|
// ieeeTable8 is the slicing8Table for IEEE
|
||
|
var ieeeTable8 *slicing8Table
|
||
|
var ieeeArchImpl bool
|
||
|
var updateIEEE func(crc uint32, p []byte) uint32
|
||
|
var ieeeOnce sync.Once
|
||
|
|
||
|
func ieeeInit() {
|
||
|
ieeeArchImpl = archAvailableIEEE()
|
||
|
|
||
|
if ieeeArchImpl {
|
||
|
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
|
||
|
}
|
||
|
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.
|
||
|
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.
|
||
|
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 }
|
||
|
|
||
|
// Update returns the result of adding the bytes in p to the crc.
|
||
|
func Update(crc uint32, tab *Table, p []byte) uint32 {
|
||
|
switch tab {
|
||
|
case castagnoliTable:
|
||
|
return updateCastagnoli(crc, p)
|
||
|
case IEEETable:
|
||
|
// 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.
|
||
|
ieeeOnce.Do(ieeeInit)
|
||
|
return updateIEEE(crc, p)
|
||
|
default:
|
||
|
return simpleUpdate(crc, tab, p)
|
||
|
}
|
||
|
}
|
||
|
|
||
|
func (d *digest) Write(p []byte) (n int, err error) {
|
||
|
switch d.tab {
|
||
|
case castagnoliTable:
|
||
|
d.crc = updateCastagnoli(d.crc, p)
|
||
|
case IEEETable:
|
||
|
// We only create digest objects through New() which takes care of
|
||
|
// initialization in this case.
|
||
|
d.crc = updateIEEE(d.crc, p)
|
||
|
default:
|
||
|
d.crc = simpleUpdate(d.crc, d.tab, p)
|
||
|
}
|
||
|
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)
|
||
|
}
|