python number handling - tiny encryption algorithm

[Scott David Daniels]

Kinsley Turner wrote:
> I'm getting a bit out of my depth porting the 'tiny encryption algorithm' 
> from C to python....
> In my version, I end up with hugely long integers, which have obviously
> not be constrained into the 4-byte unsigned longs that TEA is expecting.
> ...
> def  teaDecipher(input,key):
>     y = input[0]
>     z = input[1]
>     n = 32
>     sum = 0xC6EF3720
>     delta=0x9E3779B9 
>     while (n > 0):
>         n -= 1
>         z -= (y << 4 ^ y >> 5) + y ^ sum + key[sum>>11 & 3];
>         sum -= delta;
>         y -= (z << 4 ^ z >> 5) + z ^ sum + key[sum&3];
>       return y,z
> 
> That seems to return hugely-long integers (around 30? digits), whereas 
 > I'd expect them to max-out at 2^32.

If you really want 32-bit arithmetic, you need to specify it.
Do you have to rewrite the C for 64-bit machines?
For example:

MASK = (1 << 32) - 1
def  teaDecipher(input, key):
      y = input[0]
      z = input[1]
      sum = 0xC6EF3720
      delta = 0x9E3779B9
      for n in range(32):
          z = MASK & (z - (y << 4 ^ y >> 5) - y ^ sum - key[sum>>11 & 3])
          sum = MASK & (sum - delta)
          y = MASK & (y - (z << 4 ^ z >> 5) - z ^ sum - key[sum&3])
      return y, z

--Scott David Daniels
scott.daniels at acm.org