From: Ken Bloom <kbloom@...>
Date: 2007-01-30T00:10:06+09:00
Subject: Re: "a string".xor("another string")

On Mon, 29 Jan 2007 05:28:59 +0900, Erik Veenstra wrote:

> I want to do an XOR of two strings:
> 
>  "a string".xor("another string")
> 
> It's not that hard to implement, but it's not fast either,
> since it walks through the data string, byte-by-byte.
> 
> Any ideas? For example: "It's memory-hungry!". Any solutions?
> 
> gegroet,
> Erik V. - http://www.erikveen.dds.nl/
> 
> ----------------------------------------------------------------
> 
>  class String
>    def xor(other)
>      if other.empty?
>        self
>      else
>        a1        = self.unpack("c*")
>        a2        = other.unpack("c*")
> 
>        a2 *= 2   while a2.length < a1.length
> 
>        a1.zip(a2).collect{|c1,c2| c1^c2}.pack("c*")
>      end
>    end
>  end
> 
> ----------------------------------------------------------------

I tried changing your code to work on machine words (on my x86) by using
"I*" instead of "c*". The result wasn't any faster. I also tried 

   class String
   def xor(other)
      ret=dup
      ret.length.times{|n| ret[n]^=other[n]}
      ret
   end
   end

once again, the result wasn't any faster. If you want fast, your best bet
is probably to write it in C.

-- 
Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/