The wireshark capture is having distorted data across bytes. I have rearranged it by nibbles in Lua script, but not getting how can i read the rearranged nibbles as a single value in order to obtain correct value.
Judging by the "Want to read a value as ..." comment where 0 512 88 was desired, it looks to me like you have 3 different fields split across 4 bytes. The only practical way I can see how to get the desired numerical results from the original data is to manipulate the bytes as follows:
It may be possible to optimize this, but here’s an implementation based on the above assumptions:
-- Rotate the 1st 2 bytes to the right and the 2nd 2 bytes to the left
local x = 0x00208005
local x_hi = bit.rshift(bit.band(x, 0xffff0000), 16)
local x_lo = bit.band(x, 0x0000ffff)
local x_hi_ror = bit.bor(bit.ror(x_hi, 4), bit.lshift(bit.band(x_hi, 0x000f), 12))
local x_lo_rol = bit.bor(bit.band(bit.rol(x_lo, 4), 0x0fff), bit.rshift(x_lo, 12))
local x_new = bit.bor(bit.lshift(x_hi_ror, 16), x_lo_rol)
print("x = " .. string.format("0x%04x", x) .. "\n" ..
"x[1] = " .. bit.rshift(bit.band(x, 0xff000000), 24) .. "\n" ..
"x[2] = " .. bit.rshift(bit.band(x, 0x00ffff00), 8) .. "\n" ..
"x[3] = " .. bit.band(x, 0x000000ff))
print("x_new = " .. string.format("0x%04x", x_new) .. "\n" ..
"x_new[1] = " .. bit.rshift(bit.band(x_new, 0xff000000), 24) .. "\n" ..
"x_new[2] = " .. bit.rshift(bit.band(x_new, 0x00ffff00), 8) .. "\n" ..
"x_new[3] = " .. bit.band(x_new, 0x000000ff))
Refer to the Lua Bit Operations Module for more information on the bit operations used in this example.
NOTE: If this answer is based on faulty assumptions and doesn't help solve your problem, then you'll have to provide more information.
Asked: 2020-09-10 08:55:32 +0000
Seen: 414 times
Last updated: Sep 11 '20
Can you add an illustration of what you mean, e.g.
or something else?
You could accumulate the nibbles by multiplying, e.g.
local byte = LoNibble + HiNibble * 16.Below is the capture: 00000000001000001000000000000101 = 0x00 0x20 0x80 0x05 Want to read a value as: 00000000001000000000000001011000 = 0 512 88
So, is there a way to rearrange it and then read it?
Not sure I follow, you have:
and you want it to be:
How are the nibbles rearranged there? You seem to have swapped the last two nibbles and then 4th and the last.
There would seem to be a typo as 0 512 88 would be
0x00 0x02 0x00 0x58and not0x00 0x20 0x00 0x58. Is that what was intended?