From: "Michael W. Ryder" <_mwryder@...>
Date: 2008-01-29T05:04:56+09:00
Subject: Re: Logical Operations on Strings

Robert Klemme wrote:
> 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.
> 

Actually I designed it that way so that I could change only part of the 
original string without having to create a mask of 0xFF for the 
remaining characters.  Your implementations look a little cleaner than 
my first try and I will probably use them in the finished version.  I 
still wonder why these weren't implemented in Ruby as I have been using 
them for over 25 years in other languages.


> 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?
>

The reason I asked is that sometimes it is easier for me to think in hex 
when creating masks for logical operations.  Plus, I learned the PCL 
codes for printing using hex and it is easier for me to use them that 
way.  In Business Basic to enter a group of hex characters into a string 
I just use A$=$1B2C062C$ to create a 4 character string.  No need to 
enter each character individually.


> 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
>