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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 crc64 implements the 64-bit cyclic redundancy check, or CRC-64,
// checksum. See https://en.wikipedia.org/wiki/Cyclic_redundancy_check for
// information.
package crc64
import (
"errors"
"hash"
"sync"
)
// The size of a CRC-64 checksum in bytes.
const Size = 8
// Predefined polynomials.
const (
// The ISO polynomial, defined in ISO 3309 and used in HDLC.
ISO = 0xD800000000000000
// The ECMA polynomial, defined in ECMA 182.
ECMA = 0xC96C5795D7870F42
)
// Table is a 256-word table representing the polynomial for efficient processing.
type Table [256]uint64
var (
slicing8TablesBuildOnce sync.Once
slicing8TableISO *[8]Table
slicing8TableECMA *[8]Table
)
func buildSlicing8TablesOnce() {
slicing8TablesBuildOnce.Do(buildSlicing8Tables)
}
func buildSlicing8Tables() {
slicing8TableISO = makeSlicingBy8Table(makeTable(ISO))
slicing8TableECMA = makeSlicingBy8Table(makeTable(ECMA))
}
// MakeTable returns a [Table] constructed from the specified polynomial.
// The contents of this [Table] must not be modified.
func MakeTable(poly uint64) *Table {
buildSlicing8TablesOnce()
switch poly {
case ISO:
return &slicing8TableISO[0]
case ECMA:
return &slicing8TableECMA[0]
default:
return makeTable(poly)
}
}
func makeTable(poly uint64) *Table {
t := new(Table)
for i := 0; i < 256; i++ {
crc := uint64(i)
for j := 0; j < 8; j++ {
if crc&1 == 1 {
crc = (crc >> 1) ^ poly
} else {
crc >>= 1
}
}
t[i] = crc
}
return t
}
func makeSlicingBy8Table(t *Table) *[8]Table {
var helperTable [8]Table
helperTable[0] = *t
for i := 0; i < 256; i++ {
crc := t[i]
for j := 1; j < 8; j++ {
crc = t[crc&0xff] ^ (crc >> 8)
helperTable[j][i] = crc
}
}
return &helperTable
}
// digest represents the partial evaluation of a checksum.
type digest struct {
crc uint64
tab *Table
}
// New creates a new hash.Hash64 computing the CRC-64 checksum using the
// polynomial represented by the [Table]. Its Sum method will lay the
// value out in big-endian byte order. The returned Hash64 also
// implements [encoding.BinaryMarshaler] and [encoding.BinaryUnmarshaler] to
// marshal and unmarshal the internal state of the hash.
func New(tab *Table) hash.Hash64 { return &digest{0, tab} }
func (d *digest) Size() int { return Size }
func (d *digest) BlockSize() int { return 1 }
func (d *digest) Reset() { d.crc = 0 }
const (
magic = "crc\x02"
marshaledSize = len(magic) + 8 + 8
)
func (d *digest) MarshalBinary() ([]byte, error) {
b := make([]byte, 0, marshaledSize)
b = append(b, magic...)
b = appendUint64(b, tableSum(d.tab))
b = appendUint64(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/crc64: invalid hash state identifier")
}
if len(b) != marshaledSize {
return errors.New("hash/crc64: invalid hash state size")
}
if tableSum(d.tab) != readUint64(b[4:]) {
return errors.New("hash/crc64: tables do not match")
}
d.crc = readUint64(b[12:])
return nil
}
// appendUint64 is semantically the same as [binary.BigEndian.AppendUint64]
// We copied this function because we can not import "encoding/binary" here.
func appendUint64(b []byte, x uint64) []byte {
return append(b,
byte(x>>56),
byte(x>>48),
byte(x>>40),
byte(x>>32),
byte(x>>24),
byte(x>>16),
byte(x>>8),
byte(x),
)
}
// readUint64 is semantically the same as [binary.BigEndian.Uint64]
// We copied this function because we can not import "encoding/binary" here.
func readUint64(b []byte) uint64 {
_ = b[7]
return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
}
func update(crc uint64, tab *Table, p []byte) uint64 {
buildSlicing8TablesOnce()
crc = ^crc
// Table comparison is somewhat expensive, so avoid it for small sizes
for len(p) >= 64 {
var helperTable *[8]Table
if *tab == slicing8TableECMA[0] {
helperTable = slicing8TableECMA
} else if *tab == slicing8TableISO[0] {
helperTable = slicing8TableISO
// For smaller sizes creating extended table takes too much time
} else if len(p) >= 2048 {
// According to the tests between various x86 and arm CPUs, 2k is a reasonable
// threshold for now. This may change in the future.
helperTable = makeSlicingBy8Table(tab)
} else {
break
}
// Update using slicing-by-8
for len(p) > 8 {
crc ^= uint64(p[0]) | uint64(p[1])<<8 | uint64(p[2])<<16 | uint64(p[3])<<24 |
uint64(p[4])<<32 | uint64(p[5])<<40 | uint64(p[6])<<48 | uint64(p[7])<<56
crc = helperTable[7][crc&0xff] ^
helperTable[6][(crc>>8)&0xff] ^
helperTable[5][(crc>>16)&0xff] ^
helperTable[4][(crc>>24)&0xff] ^
helperTable[3][(crc>>32)&0xff] ^
helperTable[2][(crc>>40)&0xff] ^
helperTable[1][(crc>>48)&0xff] ^
helperTable[0][crc>>56]
p = p[8:]
}
}
// For reminders or small sizes
for _, v := range p {
crc = tab[byte(crc)^v] ^ (crc >> 8)
}
return ^crc
}
// Update returns the result of adding the bytes in p to the crc.
func Update(crc uint64, tab *Table, p []byte) uint64 {
return update(crc, tab, p)
}
func (d *digest) Write(p []byte) (n int, err error) {
d.crc = update(d.crc, d.tab, p)
return len(p), nil
}
func (d *digest) Sum64() uint64 { return d.crc }
func (d *digest) Sum(in []byte) []byte {
s := d.Sum64()
return append(in, byte(s>>56), byte(s>>48), byte(s>>40), byte(s>>32), byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
}
// Checksum returns the CRC-64 checksum of data
// using the polynomial represented by the [Table].
func Checksum(data []byte, tab *Table) uint64 { return update(0, tab, data) }
// tableSum returns the ISO checksum of table t.
func tableSum(t *Table) uint64 {
var a [2048]byte
b := a[:0]
if t != nil {
for _, x := range t {
b = appendUint64(b, x)
}
}
return Checksum(b, MakeTable(ISO))
}
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