Added ROT13 ciphering algorithm

ROT13_Cipher/Lua/Yonaba/rot13.lua

@@ -0,0 +1,32 @@
+-- ROT13 ciphering algorithm implementation
+-- See: http://en.wikipedia.org/wiki/ROT13
+
+-- Returns the ASCII bytecode of either 'a' or 'A'
+local function ascii_base(s)
+  return s:lower() == s and ('a'):byte() or ('A'):byte()
+end
+
+-- ROT13 is based on Caesar ciphering algorithm, using 13 as a key
+local function caesar_cipher(str, key)
+  return (str:gsub('%a', function(s)
+    local base = ascii_base(s)
+    return string.char(((s:byte() - base + key) % 26) + base)
+  end))
+end
+
+-- str     : a string to be ciphered
+-- returns : the ciphered string
+local function rot13_cipher(str)
+  return caesar_cipher(str, 13)
+end
+
+-- str     : a string to be deciphered
+-- returns : the deciphered string
+local function rot13_decipher(str) 
+  return caesar_cipher(str, -13) 
+end
+
+return {
+  cipher   = rot13_cipher,
+  decipher = rot13_decipher,
+}

ROT13_Cipher/Lua/Yonaba/rot13_test.lua

@@ -0,0 +1,36 @@
+-- Tests for rot13.lua
+local ROT13 = require 'rot13'
+
+local total, pass = 0, 0
+
+local function dec(str, len)
+  return #str < len
+     and str .. (('.'):rep(len-#str))
+      or str:sub(1,len)
+end
+
+local function run(message, f)
+  total = total + 1
+  local ok, err = pcall(f)
+  if ok then pass = pass + 1 end
+  local status = ok and 'PASSED' or 'FAILED'
+  print(('%02d. %68s: %s'):format(total, dec(message,68), status))
+end
+
+run('Ciphering test', function()
+  assert(ROT13.cipher('abcd') == 'nopq')
+  assert(ROT13.cipher('WXYZ') == 'JKLM')
+  assert(ROT13.cipher('abcdefghijklmnopqrstuvwxyz') == 'nopqrstuvwxyzabcdefghijklm')
+  assert(ROT13.cipher('ABCDEFGHIJKLMNOPQRSTUVWXYZ') == 'NOPQRSTUVWXYZABCDEFGHIJKLM')
+end)
+
+run('Deciphering test', function()
+  assert(ROT13.decipher('nopq') == 'abcd')
+  assert(ROT13.decipher('JKLM') == 'WXYZ')
+  assert(ROT13.decipher('nopqrstuvwxyzabcdefghijklm') == 'abcdefghijklmnopqrstuvwxyz')
+  assert(ROT13.decipher('NOPQRSTUVWXYZABCDEFGHIJKLM') == 'ABCDEFGHIJKLMNOPQRSTUVWXYZ')
+end)
+
+print(('-'):rep(80))
+print(('Total : %02d: Pass: %02d - Failed : %02d - Success: %.2f %%')
+  :format(total, pass, total-pass, (pass*100/total)))