From: Robert Klemme <shortcutter@...>
Date: 2008-01-28T19:09:14+09:00
Subject: Re: Logical Operations on Strings

2008/1/28, Michael W. Ryder <_mwryder@worldnet.att.net>:
> Is there a bitwise and for strings that I am missing?  I tried the
> documentation and Google with no luck.  I coded a simple method to
> handle this, it obviously needs more error checking, but don't want to
> reinvent the wheel if not necessary.
>
> def AND(s, m)
>    t = s.dup
>    for i in 0...(s.size <= m.size ? s.size : m.size)
>      t[i] = (s[i] & m[i]).chr
>    end
>    return t
> end

I believe this implementation is flawed because it returns a string
that is too long if self.size > m.size.

This is what I'd probably do

class String
  def &(s)
    t = ""
    [size, s.size].min.times do |i|
      t << (self[i] & s[i])
    end
    t
  end

  def |(s)
    t = ""
    [size, s.size].max.times do |i|
      t << ((self[i] || 0) | (s[i] || 0))
    end
    t
  end
end

Now you can do

irb(main):020:0> 0.chr | "a"
=> "a"
irb(main):021:0> 0.chr | "abc"
=> "abc"
irb(main):022:0> 0.chr & "abc"
=> "\000"
irb(main):023:0> a="s"
=> "s"
irb(main):024:0> a|="123"
=> "s23"
irb(main):025:0> a&="\012"
=> "\002"

> On a related note, is there any way to create a string from a hex number
> other than separating each two digits and using .chr to convert them to
> a number and adding them to the string?  If I have a string such as
> 0x7FFFFFFFFFFF I have to use something like str1 = 0x7F.chr followed by
> 5 str1 << 0xFF.chr which seems to be unnecessarily clumsy.

I am not sure which direction you mean (there is no such thing as a
"hex number" in Ruby, a number is a number, hex is just one
representation - internally they are most likely stored binary).  Does
this help?

irb(main):001:0> 123.to_s 16
=> "7b"
irb(main):002:0> "%04x" % 123
=> "007b"
irb(main):003:0> "7b".to_i 16
=> 123

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end