diff options
author | Tomasz Moń <desowin@gmail.com> | 2019-07-23 16:15:51 +0200 |
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committer | Peter Wu <peter@lekensteyn.nl> | 2019-07-29 20:49:09 +0000 |
commit | 53ecc16079ee518e3b83df352a389d04543fcac3 (patch) | |
tree | f533e93ddd91483a06b87882ca1220f2b3155ffe /wsutil/crc5.c | |
parent | d89eb91eaf36919e20678ffc8e6a237b3ac7b7ce (diff) |
USBLL: Verify Token/Split packets CRC-5
Ping-Bug: 15908
Change-Id: I25aaf772d3d0af2f459a1ad78d8253344ed13f05
Reviewed-on: https://code.wireshark.org/review/34025
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Diffstat (limited to 'wsutil/crc5.c')
-rw-r--r-- | wsutil/crc5.c | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/wsutil/crc5.c b/wsutil/crc5.c new file mode 100644 index 0000000000..2fc56a2fad --- /dev/null +++ b/wsutil/crc5.c @@ -0,0 +1,68 @@ +/* crc5.c + * CRC-5 routine + * + * 2019 Tomasz Mon <desowin@gmail.com> + * + * Wireshark - Network traffic analyzer + * By Gerald Combs <gerald@wireshark.org> + * Copyright 1998 Gerald Combs + * + * SPDX-License-Identifier: GPL-2.0-or-later + */ + +#include "config.h" + +#include <glib.h> +#include <wsutil/crc5.h> + +static guint8 crc5_usb_bits(guint32 v, int vl, guint8 ival) +{ + /* This function is based on code posted by John Sullivan to Wireshark-dev + * mailing list on Jul 21, 2019. + * + * "One of the properties of LFSRs is that a 1 bit in the input toggles a + * completely predictable set of register bits *at any point in the + * future*. This isn't often useful for most CRC caculations on variable + * sized input, as the cost of working out which those bits are vastly + * outweighs most other methods." + * + * In USB 2.0, the CRC5 is calculated on either 11 or 19 bits inputs, + * and thus this approach is viable. + */ + guint8 rv = ival; + static const guint8 bvals[19] = { + 0x1e, 0x15, 0x03, 0x06, 0x0c, 0x18, 0x19, 0x1b, + 0x1f, 0x17, 0x07, 0x0e, 0x1c, 0x11, 0x0b, 0x16, + 0x05, 0x0a, 0x14 + }; + + for (int i = 0; i < vl; i++) { + if (v & (1 << i)) { + rv ^= bvals[19 - vl + i]; + } + } + return rv; +} + +guint8 crc5_usb_11bit_input(guint16 input) +{ + return crc5_usb_bits(input, 11, 0x02); +} + +guint8 crc5_usb_19bit_input(guint32 input) +{ + return crc5_usb_bits(input, 19, 0x1d); +} + +/* + * Editor modelines - https://www.wireshark.org/tools/modelines.html + * + * Local variables: + * c-basic-offset: 4 + * tab-width: 8 + * indent-tabs-mode: nil + * End: + * + * vi: set shiftwidth=4 tabstop=8 expandtab: + * :indentSize=4:tabSize=8:noTabs=true: + */ |