2012-03-27 23:13:14 +00:00
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// 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 http://en.wikipedia.org/wiki/Cyclic_redundancy_check for
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// information.
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package crc64
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import "hash"
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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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2017-10-07 00:16:47 +00:00
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var (
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slicing8TableISO = makeSlicingBy8Table(makeTable(ISO))
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slicing8TableECMA = makeSlicingBy8Table(makeTable(ECMA))
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)
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2017-04-10 11:32:00 +00:00
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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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2012-03-27 23:13:14 +00:00
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func MakeTable(poly uint64) *Table {
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2017-10-07 00:16:47 +00:00
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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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2012-03-27 23:13:14 +00:00
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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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2017-10-07 00:16:47 +00:00
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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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2012-03-27 23:13:14 +00:00
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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
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// using the polynomial represented by the Table.
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2017-04-10 11:32:00 +00:00
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// Its Sum method will lay the value out in big-endian byte order.
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2012-03-27 23:13:14 +00:00
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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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func update(crc uint64, tab *Table, p []byte) uint64 {
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crc = ^crc
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2017-10-07 00:16:47 +00:00
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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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2012-03-27 23:13:14 +00:00
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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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2014-09-21 17:33:12 +00:00
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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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2012-03-27 23:13:14 +00:00
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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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