ROT13 implementation in various languages

[Philippe Lhoste <PhiLho@...>]

Just found a page, similar to the 99 Bottles of Beer on the Wall page, 
which mentions Lua. The purpose is simple, a bit less trivial than Hello 
World, though: to implement the ROT13 algorithm 
<http://en.wikipedia.org/wiki/Rot13 >.

Oh, it is Roberto which implemented the algorithm! In Lua 4.

Before finding this page, I have made my own implementation (Lua 5), 
given below in case somebody might be interested...

#!Lua-5.0.exe
-- ROT-13 text.
-- http://en.wikipedia.org/wiki/Rot13
-- by Philippe Lhoste <PhiLho(a)GMX.net> http://Phi.Lho.free.fr
-- v. 1.0 -- 2004/10/21 -- Creation

local text = "Put text to rotate here"

function Rotate13(t)
  return (string.gsub(t, "[%a]",
    function (char)
      local bUpper = (char < 'a')
      local b = string.byte(string.upper(char)) - 65 -- 0 to 25
      b = math.mod(b  + 13, 26)
      if bUpper then
        return string.char(b + 65)
      else
        return string.char(b + 97)
      end
    end
  ))
end

print(Rotate13(text))

One may make it more concise, but I often prefer readability over 
terseness...
OK, I rewrite this to follow Roberto ideas. I have some hard time to 
integrate (not forget) the "b and v1 or v2" paradigm, which is quite 
similar to the C "b ? v1 : v2" which I missed when writing the code 
above. Sigh.

function Rotate13(t)
  local byte_a, byte_A = string.byte('a'), string.byte('A')
  return (string.gsub(t, "[%a]",
      function (char)
        local offset = (char < 'a') and byte_A or byte_a
        local b = string.byte(char) - offset -- 0 to 25
        b = math.mod(b  + 13, 26) + offset -- Rotate
        return string.char(b)
      end
    ))
end

Also more elegant because it doesn't rely on numeric Ascii values 
(although Roberto let a '97' slip in the code...).

--
Philippe Lhoste
--  (near) Paris -- France
--  Professional programmer and amateur artist
--  http://Phi.Lho.free.fr
--  --  --  --  --  --  --  --  --  --  --  --