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 crc64 implements the 64-bit cyclic redundancy check, or CRC-64, 6 // checksum. See http://en.wikipedia.org/wiki/Cyclic_redundancy_check for 7 // information. 8 package crc64 9 10 import "hash" 11 12 // The size of a CRC-64 checksum in bytes. 13 const Size = 8 14 15 // Predefined polynomials. 16 const ( 17 // The ISO polynomial, defined in ISO 3309 and used in HDLC. 18 ISO = 0xD800000000000000 19 20 // The ECMA polynomial, defined in ECMA 182. 21 ECMA = 0xC96C5795D7870F42 22 ) 23 24 // Table is a 256-word table representing the polynomial for efficient processing. 25 type Table [256]uint64 26 27 // MakeTable returns the Table constructed from the specified polynomial. 28 func MakeTable(poly uint64) *Table { 29 t := new(Table) 30 for i := 0; i < 256; i++ { 31 crc := uint64(i) 32 for j := 0; j < 8; j++ { 33 if crc&1 == 1 { 34 crc = (crc >> 1) ^ poly 35 } else { 36 crc >>= 1 37 } 38 } 39 t[i] = crc 40 } 41 return t 42 } 43 44 // digest represents the partial evaluation of a checksum. 45 type digest struct { 46 crc uint64 47 tab *Table 48 } 49 50 // New creates a new hash.Hash64 computing the CRC-64 checksum 51 // using the polynomial represented by the Table. 52 func New(tab *Table) hash.Hash64 { return &digest{0, tab} } 53 54 func (d *digest) Size() int { return Size } 55 56 func (d *digest) BlockSize() int { return 1 } 57 58 func (d *digest) Reset() { d.crc = 0 } 59 60 func update(crc uint64, tab *Table, p []byte) uint64 { 61 crc = ^crc 62 for _, v := range p { 63 crc = tab[byte(crc)^v] ^ (crc >> 8) 64 } 65 return ^crc 66 } 67 68 // Update returns the result of adding the bytes in p to the crc. 69 func Update(crc uint64, tab *Table, p []byte) uint64 { 70 return update(crc, tab, p) 71 } 72 73 func (d *digest) Write(p []byte) (n int, err error) { 74 d.crc = update(d.crc, d.tab, p) 75 return len(p), nil 76 } 77 78 func (d *digest) Sum64() uint64 { return d.crc } 79 80 func (d *digest) Sum(in []byte) []byte { 81 s := d.Sum64() 82 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)) 83 } 84 85 // Checksum returns the CRC-64 checksum of data 86 // using the polynomial represented by the Table. 87 func Checksum(data []byte, tab *Table) uint64 { return update(0, tab, data) } 88
