在python中将32位解释为Integer

Question

I read bits from a file. The first value is

bits = str(11101111010110011000000000000001)

This is the binary representation of a signed 32 bit integer so this is already in two's complement and little endian. I think the value I want to get is

-279347199

atleast this website converts it as such http://www.binaryconvert.com/result_signed_int.html?hexadecimal=EF598001

everything I found that solves this problem interprets the bits as pure binary without two's complement and little endian

Answer 1

A neat trick to convert from two's complement is to find 1 from the end and replace rest of the bits by their complement.

def convert_from_twosc(bits):
    bits = bits[::-1]
    for bit in bits:
        if bit == '1':
            for new_bit in range(bits.index(bit) + 1, len(bits)):
                if bits[new_bit] == '0':
                    bits[new_bit] = '1'
                else:
                    bits[new_bit] = '0'
            break
    return "".join(map(str, bits[::-1]))
bits = input()
number = int(convert_from_twosc(list(bits)) , 2) * -1
print(number)

Output:

11101111010110011000000000000001
-279347199

This function always assumes input to it, is a signed negative number so be careful.