mirror of
https://github.com/autc04/Retro68.git
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225 lines
5.6 KiB
Go
225 lines
5.6 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package crc64 implements the 64-bit cyclic redundancy check, or CRC-64,
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// checksum. See https://en.wikipedia.org/wiki/Cyclic_redundancy_check for
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// information.
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package crc64
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import (
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"errors"
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"hash"
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"sync"
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)
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// The size of a CRC-64 checksum in bytes.
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const Size = 8
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// Predefined polynomials.
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const (
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// The ISO polynomial, defined in ISO 3309 and used in HDLC.
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ISO = 0xD800000000000000
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// The ECMA polynomial, defined in ECMA 182.
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ECMA = 0xC96C5795D7870F42
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)
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// Table is a 256-word table representing the polynomial for efficient processing.
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type Table [256]uint64
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var (
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slicing8TablesBuildOnce sync.Once
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slicing8TableISO *[8]Table
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slicing8TableECMA *[8]Table
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)
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func buildSlicing8TablesOnce() {
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slicing8TablesBuildOnce.Do(buildSlicing8Tables)
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}
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func buildSlicing8Tables() {
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slicing8TableISO = makeSlicingBy8Table(makeTable(ISO))
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slicing8TableECMA = makeSlicingBy8Table(makeTable(ECMA))
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}
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// MakeTable returns a Table constructed from the specified polynomial.
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// The contents of this Table must not be modified.
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func MakeTable(poly uint64) *Table {
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buildSlicing8TablesOnce()
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switch poly {
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case ISO:
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return &slicing8TableISO[0]
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case ECMA:
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return &slicing8TableECMA[0]
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default:
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return makeTable(poly)
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}
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}
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func makeTable(poly uint64) *Table {
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t := new(Table)
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for i := 0; i < 256; i++ {
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crc := uint64(i)
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for j := 0; j < 8; j++ {
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if crc&1 == 1 {
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crc = (crc >> 1) ^ poly
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} else {
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crc >>= 1
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}
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}
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t[i] = crc
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}
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return t
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}
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func makeSlicingBy8Table(t *Table) *[8]Table {
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var helperTable [8]Table
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helperTable[0] = *t
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for i := 0; i < 256; i++ {
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crc := t[i]
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for j := 1; j < 8; j++ {
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crc = t[crc&0xff] ^ (crc >> 8)
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helperTable[j][i] = crc
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}
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}
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return &helperTable
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}
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// digest represents the partial evaluation of a checksum.
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type digest struct {
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crc uint64
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tab *Table
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}
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// New creates a new hash.Hash64 computing the CRC-64 checksum using the
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// polynomial represented by the Table. Its Sum method will lay the
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// value out in big-endian byte order. The returned Hash64 also
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// implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to
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// marshal and unmarshal the internal state of the hash.
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func New(tab *Table) hash.Hash64 { return &digest{0, tab} }
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func (d *digest) Size() int { return Size }
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func (d *digest) BlockSize() int { return 1 }
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func (d *digest) Reset() { d.crc = 0 }
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const (
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magic = "crc\x02"
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marshaledSize = len(magic) + 8 + 8
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)
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func (d *digest) MarshalBinary() ([]byte, error) {
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b := make([]byte, 0, marshaledSize)
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b = append(b, magic...)
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b = appendUint64(b, tableSum(d.tab))
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b = appendUint64(b, d.crc)
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return b, nil
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}
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func (d *digest) UnmarshalBinary(b []byte) error {
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if len(b) < len(magic) || string(b[:len(magic)]) != magic {
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return errors.New("hash/crc64: invalid hash state identifier")
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}
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if len(b) != marshaledSize {
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return errors.New("hash/crc64: invalid hash state size")
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}
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if tableSum(d.tab) != readUint64(b[4:]) {
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return errors.New("hash/crc64: tables do not match")
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}
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d.crc = readUint64(b[12:])
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return nil
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}
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func appendUint64(b []byte, x uint64) []byte {
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a := [8]byte{
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byte(x >> 56),
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byte(x >> 48),
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byte(x >> 40),
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byte(x >> 32),
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byte(x >> 24),
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byte(x >> 16),
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byte(x >> 8),
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byte(x),
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}
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return append(b, a[:]...)
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}
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func readUint64(b []byte) uint64 {
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_ = b[7]
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return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
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uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
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}
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func update(crc uint64, tab *Table, p []byte) uint64 {
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buildSlicing8TablesOnce()
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crc = ^crc
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// Table comparison is somewhat expensive, so avoid it for small sizes
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for len(p) >= 64 {
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var helperTable *[8]Table
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if *tab == slicing8TableECMA[0] {
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helperTable = slicing8TableECMA
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} else if *tab == slicing8TableISO[0] {
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helperTable = slicing8TableISO
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// For smaller sizes creating extended table takes too much time
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} else if len(p) > 16384 {
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helperTable = makeSlicingBy8Table(tab)
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} else {
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break
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}
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// Update using slicing-by-8
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for len(p) > 8 {
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crc ^= uint64(p[0]) | uint64(p[1])<<8 | uint64(p[2])<<16 | uint64(p[3])<<24 |
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uint64(p[4])<<32 | uint64(p[5])<<40 | uint64(p[6])<<48 | uint64(p[7])<<56
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crc = helperTable[7][crc&0xff] ^
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helperTable[6][(crc>>8)&0xff] ^
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helperTable[5][(crc>>16)&0xff] ^
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helperTable[4][(crc>>24)&0xff] ^
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helperTable[3][(crc>>32)&0xff] ^
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helperTable[2][(crc>>40)&0xff] ^
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helperTable[1][(crc>>48)&0xff] ^
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helperTable[0][crc>>56]
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p = p[8:]
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}
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}
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// For reminders or small sizes
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for _, v := range p {
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crc = tab[byte(crc)^v] ^ (crc >> 8)
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}
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return ^crc
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}
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// Update returns the result of adding the bytes in p to the crc.
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func Update(crc uint64, tab *Table, p []byte) uint64 {
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return update(crc, tab, p)
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}
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func (d *digest) Write(p []byte) (n int, err error) {
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d.crc = update(d.crc, d.tab, p)
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return len(p), nil
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}
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func (d *digest) Sum64() uint64 { return d.crc }
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func (d *digest) Sum(in []byte) []byte {
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s := d.Sum64()
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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))
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}
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// Checksum returns the CRC-64 checksum of data
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// using the polynomial represented by the Table.
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func Checksum(data []byte, tab *Table) uint64 { return update(0, tab, data) }
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// tableSum returns the ISO checksum of table t.
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func tableSum(t *Table) uint64 {
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var a [2048]byte
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b := a[:0]
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if t != nil {
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for _, x := range t {
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b = appendUint64(b, x)
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}
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}
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return Checksum(b, MakeTable(ISO))
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}
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