libgo/go/hash/crc32/crc32.go

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Package crc32 implements the 32-bit cyclic redundancy check, or CRC-32,
   6 // checksum. See https://en.wikipedia.org/wiki/Cyclic_redundancy_check for
   7 // information.
   8 //
   9 // Polynomials are represented in LSB-first form also known as reversed representation.
  10 //
  11 // See https://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks#Reversed_representations_and_reciprocal_polynomials
  12 // for information.
  13 package crc32
  14
  15 import (
  16         "errors"
  17         "hash"
  18         "sync"
  19 )
  20
  21 // The size of a CRC-32 checksum in bytes.
  22 const Size = 4
  23
  24 // Predefined polynomials.
  25 const (
  26         // IEEE is by far and away the most common CRC-32 polynomial.
  27         // Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...
  28         IEEE = 0xedb88320
  29
  30         // Castagnoli's polynomial, used in iSCSI.
  31         // Has better error detection characteristics than IEEE.
  32         // https://dx.doi.org/10.1109/26.231911
  33         Castagnoli = 0x82f63b78
  34
  35         // Koopman's polynomial.
  36         // Also has better error detection characteristics than IEEE.
  37         // https://dx.doi.org/10.1109/DSN.2002.1028931
  38         Koopman = 0xeb31d82e
  39 )
  40
  41 // Table is a 256-word table representing the polynomial for efficient processing.
  42 type Table [256]uint32
  43
  44 // This file makes use of functions implemented in architecture-specific files.
  45 // The interface that they implement is as follows:
  46 //
  47 //    // archAvailableIEEE reports whether an architecture-specific CRC32-IEEE
  48 //    // algorithm is available.
  49 //    archAvailableIEEE() bool
  50 //
  51 //    // archInitIEEE initializes the architecture-specific CRC3-IEEE algorithm.
  52 //    // It can only be called if archAvailableIEEE() returns true.
  53 //    archInitIEEE()
  54 //
  55 //    // archUpdateIEEE updates the given CRC32-IEEE. It can only be called if
  56 //    // archInitIEEE() was previously called.
  57 //    archUpdateIEEE(crc uint32, p []byte) uint32
  58 //
  59 //    // archAvailableCastagnoli reports whether an architecture-specific
  60 //    // CRC32-C algorithm is available.
  61 //    archAvailableCastagnoli() bool
  62 //
  63 //    // archInitCastagnoli initializes the architecture-specific CRC32-C
  64 //    // algorithm. It can only be called if archAvailableCastagnoli() returns
  65 //    // true.
  66 //    archInitCastagnoli()
  67 //
  68 //    // archUpdateCastagnoli updates the given CRC32-C. It can only be called
  69 //    // if archInitCastagnoli() was previously called.
  70 //    archUpdateCastagnoli(crc uint32, p []byte) uint32
  71
  72 // castagnoliTable points to a lazily initialized Table for the Castagnoli
  73 // polynomial. MakeTable will always return this value when asked to make a
  74 // Castagnoli table so we can compare against it to find when the caller is
  75 // using this polynomial.
  76 var castagnoliTable *Table
  77 var castagnoliTable8 *slicing8Table
  78 var castagnoliArchImpl bool
  79 var updateCastagnoli func(crc uint32, p []byte) uint32
  80 var castagnoliOnce sync.Once
  81
  82 func castagnoliInit() {
  83         castagnoliTable = simpleMakeTable(Castagnoli)
  84         castagnoliArchImpl = archAvailableCastagnoli()
  85
  86         if castagnoliArchImpl {
  87                 archInitCastagnoli()
  88                 updateCastagnoli = archUpdateCastagnoli
  89         } else {
  90                 // Initialize the slicing-by-8 table.
  91                 castagnoliTable8 = slicingMakeTable(Castagnoli)
  92                 updateCastagnoli = func(crc uint32, p []byte) uint32 {
  93                         return slicingUpdate(crc, castagnoliTable8, p)
  94                 }
  95         }
  96 }
  97
  98 // IEEETable is the table for the IEEE polynomial.
  99 var IEEETable = simpleMakeTable(IEEE)
 100
 101 // ieeeTable8 is the slicing8Table for IEEE
 102 var ieeeTable8 *slicing8Table
 103 var ieeeArchImpl bool
 104 var updateIEEE func(crc uint32, p []byte) uint32
 105 var ieeeOnce sync.Once
 106
 107 func ieeeInit() {
 108         ieeeArchImpl = archAvailableIEEE()
 109
 110         if ieeeArchImpl {
 111                 archInitIEEE()
 112                 updateIEEE = archUpdateIEEE
 113         } else {
 114                 // Initialize the slicing-by-8 table.
 115                 ieeeTable8 = slicingMakeTable(IEEE)
 116                 updateIEEE = func(crc uint32, p []byte) uint32 {
 117                         return slicingUpdate(crc, ieeeTable8, p)
 118                 }
 119         }
 120 }
 121
 122 // MakeTable returns a Table constructed from the specified polynomial.
 123 // The contents of this Table must not be modified.
 124 func MakeTable(poly uint32) *Table {
 125         switch poly {
 126         case IEEE:
 127                 ieeeOnce.Do(ieeeInit)
 128                 return IEEETable
 129         case Castagnoli:
 130                 castagnoliOnce.Do(castagnoliInit)
 131                 return castagnoliTable
 132         }
 133         return simpleMakeTable(poly)
 134 }
 135
 136 // digest represents the partial evaluation of a checksum.
 137 type digest struct {
 138         crc uint32
 139         tab *Table
 140 }
 141
 142 // New creates a new hash.Hash32 computing the CRC-32 checksum using the
 143 // polynomial represented by the Table. Its Sum method will lay the
 144 // value out in big-endian byte order. The returned Hash32 also
 145 // implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to
 146 // marshal and unmarshal the internal state of the hash.
 147 func New(tab *Table) hash.Hash32 {
 148         if tab == IEEETable {
 149                 ieeeOnce.Do(ieeeInit)
 150         }
 151         return &digest{0, tab}
 152 }
 153
 154 // NewIEEE creates a new hash.Hash32 computing the CRC-32 checksum using
 155 // the IEEE polynomial. Its Sum method will lay the value out in
 156 // big-endian byte order. The returned Hash32 also implements
 157 // encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to marshal
 158 // and unmarshal the internal state of the hash.
 159 func NewIEEE() hash.Hash32 { return New(IEEETable) }
 160
 161 func (d *digest) Size() int { return Size }
 162
 163 func (d *digest) BlockSize() int { return 1 }
 164
 165 func (d *digest) Reset() { d.crc = 0 }
 166
 167 const (
 168         magic         = "crc\x01"
 169         marshaledSize = len(magic) + 4 + 4
 170 )
 171
 172 func (d *digest) MarshalBinary() ([]byte, error) {
 173         b := make([]byte, 0, marshaledSize)
 174         b = append(b, magic...)
 175         b = appendUint32(b, tableSum(d.tab))
 176         b = appendUint32(b, d.crc)
 177         return b, nil
 178 }
 179
 180 func (d *digest) UnmarshalBinary(b []byte) error {
 181         if len(b) < len(magic) || string(b[:len(magic)]) != magic {
 182                 return errors.New("hash/crc32: invalid hash state identifier")
 183         }
 184         if len(b) != marshaledSize {
 185                 return errors.New("hash/crc32: invalid hash state size")
 186         }
 187         if tableSum(d.tab) != readUint32(b[4:]) {
 188                 return errors.New("hash/crc32: tables do not match")
 189         }
 190         d.crc = readUint32(b[8:])
 191         return nil
 192 }
 193
 194 func appendUint32(b []byte, x uint32) []byte {
 195         a := [4]byte{
 196                 byte(x >> 24),
 197                 byte(x >> 16),
 198                 byte(x >> 8),
 199                 byte(x),
 200         }
 201         return append(b, a[:]...)
 202 }
 203
 204 func readUint32(b []byte) uint32 {
 205         _ = b[3]
 206         return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
 207 }
 208
 209 // Update returns the result of adding the bytes in p to the crc.
 210 func Update(crc uint32, tab *Table, p []byte) uint32 {
 211         switch tab {
 212         case castagnoliTable:
 213                 return updateCastagnoli(crc, p)
 214         case IEEETable:
 215                 // Unfortunately, because IEEETable is exported, IEEE may be used without a
 216                 // call to MakeTable. We have to make sure it gets initialized in that case.
 217                 ieeeOnce.Do(ieeeInit)
 218                 return updateIEEE(crc, p)
 219         default:
 220                 return simpleUpdate(crc, tab, p)
 221         }
 222 }
 223
 224 func (d *digest) Write(p []byte) (n int, err error) {
 225         switch d.tab {
 226         case castagnoliTable:
 227                 d.crc = updateCastagnoli(d.crc, p)
 228         case IEEETable:
 229                 // We only create digest objects through New() which takes care of
 230                 // initialization in this case.
 231                 d.crc = updateIEEE(d.crc, p)
 232         default:
 233                 d.crc = simpleUpdate(d.crc, d.tab, p)
 234         }
 235         return len(p), nil
 236 }
 237
 238 func (d *digest) Sum32() uint32 { return d.crc }
 239
 240 func (d *digest) Sum(in []byte) []byte {
 241         s := d.Sum32()
 242         return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
 243 }
 244
 245 // Checksum returns the CRC-32 checksum of data
 246 // using the polynomial represented by the Table.
 247 func Checksum(data []byte, tab *Table) uint32 { return Update(0, tab, data) }
 248
 249 // ChecksumIEEE returns the CRC-32 checksum of data
 250 // using the IEEE polynomial.
 251 func ChecksumIEEE(data []byte) uint32 {
 252         ieeeOnce.Do(ieeeInit)
 253         return updateIEEE(0, data)
 254 }
 255
 256 // tableSum returns the IEEE checksum of table t.
 257 func tableSum(t *Table) uint32 {
 258         var a [1024]byte
 259         b := a[:0]
 260         if t != nil {
 261                 for _, x := range t {
 262                         b = appendUint32(b, x)
 263                 }
 264         }
 265         return ChecksumIEEE(b)
 266 }