Got nerd sniped by a terrible interview question

mult.py

#!/usr/bin/env python3

# Let's pretend we have to implement 32-bit multiplication with just
# addition, subtraction, equality/inequality tests, and bit twiddling
# (shifts and bitwise logical ops). For bonus points detect overflow
# and signal via an exception.

# A friend got asked this on an interview. It is a terrible interview
# question unless possibly you're interviewing someone to be a junior
# chip designer or something. But it nerd sniped me anyway as an
# amusing thing to spend a little time on in the comfort of my own
# home.

import sys

multiplier, multiplicand = [int(x) for x in sys.argv[1:]]

r0 = multiplier
r1 = multiplicand
acc = 0

high_bit = 1 << 31

bits = (1 << 32) - 1

while r0 != 0:

    if r0 & 1 != 0:

        # Check for overflow before we do addition.
        limit = bits & (~ acc)
        r2 = r1
        overflow = False

        while limit != r2:

            if r2 == 0:
                overflow = False
                break

            if (r2 & 1) != 0 and (limit & 1) == 0:
                overflow = True
            elif (r2 & 1) == 0 and (limit & 1) != 0:
                overflow = False

            limit >>= 1
            r2 >>= 1

        if overflow:
            raise Exception("Overflow in addition.")

        acc += r1

    r0 >>= 1

    # Check for overflow if we're about to shift off an on 32nd bit
    # and there is still multiplication left to do.
    if (high_bit & r1) != 0 and r0 != 0:
        raise Exception("Overflow in shift")

    r1 <<= 1

print(f"{multiplier} x {multiplicand} = {acc} ({multiplier * multiplicand == acc})")