94 lines
2.3 KiB
Go
94 lines
2.3 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 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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// MakeTable returns the Table constructed from the specified polynomial.
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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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// 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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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) 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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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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in = append(in, byte(s>>56))
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in = append(in, byte(s>>48))
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in = append(in, byte(s>>40))
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in = append(in, byte(s>>32))
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in = append(in, byte(s>>24))
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in = append(in, byte(s>>16))
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in = append(in, byte(s>>8))
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in = append(in, byte(s))
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return in
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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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