brannerchinese brannerchinese - 1 year ago 128
Python Question

Simulating integer overflow in Python

Python 2 has two integer datatypes

, 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 Source

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
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