# /* ================== */
# /* text_compressor.js */
# /* ================== */
function compress(string)
{
// Get the unique characters and numeric base.
var unique = create_set(string);
var base = unique.length;
// Create a key that will encode data properly.
shuffle(unique);
var mapping = create_dict(unique);
while (!mapping[string[string.length - 1]])
{
shuffle(unique);
mapping = create_dict(unique);
}
// Create a compressed numeric representation.
var value = BigInteger();
for (var place = 0; place < string.length; place++)
{
var multiple = BigInteger(base).pow(place);
var product = BigInteger(mapping[string[place]]).multiply(multiple);
value = value.add(product);
}
// Return the number as a string with the table.
return [array_to_string(decode(value)), unique.join("")];
}
function create_set(string)
{
var set = new Object();
for (var index = 0; index < string.length; index++)
{
set[string[index]] = 0;
}
var array = new Array();
for (var value in set)
{
array.push(value);
}
return array;
}
function shuffle(array)
{
var range = array.length - 1;
for (var index = 0; index < array.length; index++)
{
var destination = Math.floor(Math.random() * range);
if (destination >= index)
{
destination++;
}
var temporary = array[destination];
array[destination] = array[index];
array[index] = temporary;
}
}
function create_dict(array)
{
var dict = new Object();
for (var index = 0; index < array.length; index++)
{
dict[array[index]] = index;
}
return dict;
}
function decode(number)
{
// Change a number into a string.
var array = new Array();
while (!number.isZero())
{
var answer = number.divRem(256);
number = answer[0];
array.push(answer[1]);
}
return array;
}
function array_to_string(array)
{
for (var index = 0; index < array.length; index++)
{
array[index] = String.fromCharCode(array[index]);
}
return array.join("");
}
function decompress(string, key)
{
// Get the numeric value of the string.
var number = encode(string);
// Find the numeric base and prepare storage.
var base = key.length;
var array = new Array();
// Decode the value into the original string.
while (!number.isZero())
{
var answer = number.divRem(base);
number = answer[0];
array.push(key[answer[1]]);
}
// Return the "string" as a bytes object.
return array.join("");
}
function encode(string)
{
// Change a string into a number.
assert(string.length > 0 && string[string.length - 1] != String.fromCharCode(0), "String has ambiguous value!");
var value = BigInteger();
for (var shift = 0; shift < string.length; shift++)
{
var multiple = BigInteger(256).pow(shift);
var product = BigInteger(string[shift].charCodeAt()).multiply(multiple);
value = value.add(product);
}
return value;
}
function assert(okay, error)
{
if (!okay)
{
alert(error);
throw new Error(error);
}
}
# /* ======== */
# /* Test.htm */
# /* ======== */
Text Compressor
Results