Simulating integer overflow in Python

Question

Python 2 has two integer datatypes int and long, and automatically converts between them as necessary, especially in order to avoid integer overflow.

I am simulating a C function in Python and am wondering if there are standard ways to re-enable integer overflow. For the nonce, I've used

overflow_point = maxint + 1
if value > overflow_point:
    value -= 2 * overflow_point

Is there a more standard way to do the same thing?

Answer 1

Use NumPy (which is written in C and exposes native machine-level integers). NumPy has these integer types:

Signed integers:

• np.int8
• np.int16
• np.int32

Unsigned integers:

• np.uint8
• np.uint16
• np.uint32

For example (notice it overflows after integer value 127):

import numpy as np

counter = np.int8(0)
one = np.int8(1)

for i in range(130):
    print(type(counter), counter)
    counter = counter + one

At any point you can convert back to a Python integer with just int(counter), for example.

Answer 2

I think the basic idea is sound, but needs some tweaks:

1. your function doesn't overflow on sys.maxint+1, but it should;
2. sys.maxint can be exceeded several times over as a result of a single operation;
3. negative values below -sys.maxint-1 also need to be considered.

With this in mind, I came up with the following:

import sys

def int_overflow(val):
  if not -sys.maxint-1 <= val <= sys.maxint:
    val = (val + (sys.maxint + 1)) % (2 * (sys.maxint + 1)) - sys.maxint - 1
  return val