Reversing byte order of negative integer with Python 3

Question

After extracting some 32-bit sign bit value and keeping that same 32-bit representation sign-extended, I now have to reverse the byte order of the value (I need to follow a precise imposed workflow).

Here is what I previously did:

• initially I have the value "11101101111110100111001110011010"
• I converted that chain to int : I get 3992613786
• I extracted the 32-bit sign bit (sign-extended): I get -302353510

Now, I have to reverse the byte order of that last value (I am supposed to get -1703675155 in the end).

Does anyone know how to reverse the byte order of a negative extended sign bit with Python3?

Answer 1

There are probably better ways but this seems to work:

from struct import pack

x = "11101101111110100111001110011010"

n = ((~int(x, 2) + 1) & 0xffffffff) * -1 if x[0] == '1' else 1


print(int.from_bytes(pack('!i', n), 'little', signed=True))

Output:

-1703675155