XORing long strings opimization?

[Casey Whitelaw]

Noen <not.available at na.no> wrote in message news:<%AWpb.24470$BD3.4569022 at juliett.dax.net>...
> Here is the result, if anyone wants it :)
> It was quite quick indeed, It took me 10.3279999495 seconds to XOR 
> "a"*1000000 large string. Im going to XOR 700000000 mb sized files, so 
> if anyone know how to make it even faster, please tell me :)
> 
> import string
> def xorstring(s1,s2):
>      """ XOR string s1 with s2 """
>      # Argument check
>      if not (type(s1) == type("")) or not (type(s2) == type("")):
>          raise TypeError, "Arguments are not strings"
>      if len(s1) != len(s2):
>          raise ValueError, "Size differs in strings"
>      # Xoring
> 
>      # Create lists
>      l1 = map(ord, s1)
>      l2 = map(ord, s2)
> 
>      # Xor it all together
>      xorlist = []
>      xorlist = [chr(x ^ y) for (x, y) in zip(l1, l2)]
>      return string.join(xorlist,"") # Backward compatible

Just fiddling around with the (excellent) suggestions already posted,
and found a couple of things.

Alex's suggestion using array is the fastest, but was slightly faster
when using xrange() rather than enumerate():

def xor6(s1, s2):
        a1 = array.array("b", s1)
        a2 = array.array("b", s2)

        for i in xrange(len(a1)):
                a1[i] ^= a2[i]
        return a1.tostring()

On my system, this XORs 500,000 characters in 0.39s, with Noen's
original taking 0.67s.

Using psyco produced a further ~3x speedup, reducing this to 0.14s.
That's pretty fast!

Casey