1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
|
require 'digest/crc16_ccitt'
module Digest
#
# Implements the CRC16_CCITT algorithm used in QT algorithms.
#
# @author Matthew Bednarski
#
class CRC16QT < CRC16CCITT
FINAL_XOR = 0xffff
REVERSE_CRC_RESULT = true
REVERSE_DATA = true
# Updates the CRC16 checksum.
#
# @param [String] data
# The data to update the checksum with.
#
def update(data)
data.each_byte do |b|
b = revert_byte(b) if REVERSE_DATA
@crc = ((TABLE[((@crc >> 8) ^ b) & 0xff] ^ (@crc << 8)) & 0xffff)
end
return self
end
def checksum
crc = @crc + 0
crc ^= FINAL_XOR if FINAL_XOR
crc = revert_bits crc if REVERSE_CRC_RESULT
return crc
end
protected
def revert_bits(cc)
ob = 0
b = (1 << 15)
16.times do |t|
ob |= (1 << t) if (cc & b) != 0
b >>= 1
end
return ob
end
def revert_byte(cc)
ob = 0
b = (1 << 7)
8.times do |t|
ob |= (1 << t) if (cc & b) != 0
b >>= 1
end
return ob
end
end
end
|
