cint: make ctypes great again

This is a wrapper for ctypes.c_* types so that the arithmetic operators works the same as in C, so:

• value overflow/underflow may occur (yeah, integer overflows are UB in C but they usually work)
• when making calculations of two different cint types, the result type will be of bigger or/and unsigned type

Install with pip install cint! Supports both Python 2 and Python 3.

TL;DR - show me an example

In [1]: x = cint.I8(127)

# Values will overflow as in C
In [2]: x + 1
Out[2]: I8(-128)

# They will also implicitly convert to the bigger/unsigned type when calculated together
In [3]: x + cint.U16(1)
Out[3]: U16(128)

# And of course, overflow on construction as well
In [4]: cint.I8(255)
Out[4]: I8(-1)

Why this lib?

Sometimes you just need the old, low level behavior of int/unsigned types. This may be handy during reverse engineering or rewritting C code to Python and persisting their integer arithmetics behavior.

Example 1

Imagine a C program returns a value you suspect to be a leak of a kernel pointer address and its returned to you as int64 e.g. -1702577226.

You can convert it to a more-readable-hex form by using c_void_p from ctypes as in:

In [2]: hex(cast(-1702577226, c_void_p).value)
Out[2]: '0xffffffff9a84bbb6'

cint makes it simpler:

In [3]: hex(cint.U64(-1702577226))
Out[3]: '0xffffffff9a84bbb6'

Example 2

cint can also be used to reimplement a RNG algorithm from C code or a reverse engineered program. This could look as:

from cint import I8, I32, U64, Cint

def rand_gen(seed):
    """Returns a rng that generates numbers in a range of given cint type"""
    assert isinstance(seed, Cint)

    while True:
        seed = 1103515245 * seed + 12345
        yield seed

# a simple I32 and U64 random number generators
rand_i32 = rand_gen(I32(1))
rand_u64 = rand_gen(U64(2))

for i in range(10):
    print("Gen %d number: i32 = %d, u64 = %d" % (i, next(rand_i32), next(rand_u64)))

Example 3

This example just shows some "weird" examples that you would not expect from normal Python integers

from cint import I8, I32, U64, Cint

# We can do simple overflows
print("I8(127) + 1 = %d" % (I8(127) + 1))

# Some other 'weird' cases are also handled - see tests for more! ;)
print("-1 * I8(-128) = %d" % (-1 * I8(-128)))
print("abs(I32.MIN) = %d" % abs(I32.MIN))

# Adding numbers of two different types will result in bigger type result
x = I32(1) + U64(2)
print("x = %r" % x)  # U64(3)

# There are also .MIN and .MAX constants
print("U64 min value = %d, max value = %d" % (U64.MIN, U64.MAX))