/src/wireshark/wsutil/crc5.c
Line | Count | Source (jump to first uncovered line) |
1 | | /* crc5.c |
2 | | * CRC-5 routine |
3 | | * |
4 | | * 2019 Tomasz Mon <desowin@gmail.com> |
5 | | * |
6 | | * Wireshark - Network traffic analyzer |
7 | | * By Gerald Combs <gerald@wireshark.org> |
8 | | * Copyright 1998 Gerald Combs |
9 | | * |
10 | | * SPDX-License-Identifier: GPL-2.0-or-later |
11 | | */ |
12 | | |
13 | | #include "config.h" |
14 | | |
15 | | #include <wsutil/crc5.h> |
16 | | |
17 | | static uint8_t crc5_usb_bits(uint32_t v, int vl, uint8_t ival) |
18 | 0 | { |
19 | | /* This function is based on code posted by John Sullivan to Wireshark-dev |
20 | | * mailing list on Jul 21, 2019. |
21 | | * |
22 | | * "One of the properties of LFSRs is that a 1 bit in the input toggles a |
23 | | * completely predictable set of register bits *at any point in the |
24 | | * future*. This isn't often useful for most CRC caculations on variable |
25 | | * sized input, as the cost of working out which those bits are vastly |
26 | | * outweighs most other methods." |
27 | | * |
28 | | * In USB 2.0, the CRC5 is calculated on either 11 or 19 bits inputs, |
29 | | * and thus this approach is viable. |
30 | | */ |
31 | 0 | uint8_t rv = ival; |
32 | 0 | static const uint8_t bvals[19] = { |
33 | 0 | 0x1e, 0x15, 0x03, 0x06, 0x0c, 0x18, 0x19, 0x1b, |
34 | 0 | 0x1f, 0x17, 0x07, 0x0e, 0x1c, 0x11, 0x0b, 0x16, |
35 | 0 | 0x05, 0x0a, 0x14 |
36 | 0 | }; |
37 | |
|
38 | 0 | for (int i = 0; i < vl; i++) { |
39 | 0 | if (v & (1 << i)) { |
40 | 0 | rv ^= bvals[19 - vl + i]; |
41 | 0 | } |
42 | 0 | } |
43 | 0 | return rv; |
44 | 0 | } |
45 | | |
46 | | uint8_t crc5_usb_11bit_input(uint16_t input) |
47 | 0 | { |
48 | 0 | return crc5_usb_bits(input, 11, 0x02); |
49 | 0 | } |
50 | | |
51 | | uint8_t crc5_usb_19bit_input(uint32_t input) |
52 | 0 | { |
53 | 0 | return crc5_usb_bits(input, 19, 0x1d); |
54 | 0 | } |
55 | | |
56 | | /* |
57 | | * Editor modelines - https://www.wireshark.org/tools/modelines.html |
58 | | * |
59 | | * Local variables: |
60 | | * c-basic-offset: 4 |
61 | | * tab-width: 8 |
62 | | * indent-tabs-mode: nil |
63 | | * End: |
64 | | * |
65 | | * vi: set shiftwidth=4 tabstop=8 expandtab: |
66 | | * :indentSize=4:tabSize=8:noTabs=true: |
67 | | */ |