/*
- Copyright (c) 2010 Ant Kutschera, maxant
- The code below is free software: you can redistribute it and/or modify
- it under the terms of the Lesser GNU General Public License as published by
- the Free Software Foundation, either version 3 of the License, or
- (at your option) any later version.
- The code in this file is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- Lesser GNU General Public License for more details.
- You should have received a copy of the Lesser GNU General Public License
- along with Foobar. If not, see http://www.gnu.org/licenses/.
*/
package uk.co.maxant.util;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
allows you to convert a whole number into a compacted representation of that number,
based upon the dictionary you provide. very similar to base64 encoding, or indeed hex
-
encoding.
*/
public class BaseX {/**
- contains hexadecimals 0-F only.
*/
public static final char[] DICTIONARY_16 =
new char[]{'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
/**
- contains only alphanumerics, in capitals and excludes letters/numbers which can be confused,
- eg. 0 and O or L and I and 1.
*/
public static final char[] DICTIONARY_32 =
new char[]{'1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','J','K','M','N','P','Q','R','S','T','U','V','W','X','Y','Z'};
/**
- contains only alphanumerics, including both capitals and smalls.
*/
public static final char[] DICTIONARY_62 =
new char[]{'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
/**
- contains alphanumerics, including both capitals and smalls, and the following special chars:
- +"@*#%&/|()=?'~[!]{}-:.,; (you might not be able to read all those using a browser!
/
public static final char[] DICTIONARY_89 =
new char[]{'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','+','"','@','','#','%','&','/','|','(',')','=','?','~','[',']','{','}','$','-','','.',':',',',';','<','>'};
protected char[] dictionary;
/**
- create an encoder with the given dictionary.
- @param dictionary the dictionary to use when encoding and decoding.
*/
public BaseX(char[] dictionary){
this.dictionary = dictionary;
}
/**
- creates an encoder with the {@link #DICTIONARY_62} dictionary.
- @param dictionary the dictionary to use when encoding and decoding.
*/
public BaseX(){
this.dictionary = DICTIONARY_62;
}
/**
- tester method.
*/
public static void main(String[] args) {
String original = "123456789012345678901234567890";
System.out.println("Original: " + original);
BaseX bx = new BaseX(DICTIONARY_62);
String encoded = bx.encode(new BigInteger(original));
System.out.println("encoded: " + encoded);
BigInteger decoded = bx.decode(encoded);
System.out.println("decoded: " + decoded);
if(original.equals(decoded.toString())){
System.out.println("Passed! decoded value is the same as the original.");
}else{
System.err.println("FAILED! decoded value is NOT the same as the original!!");
}
}
/**
encodes the given string into the base of the dictionary provided in the constructor.
@param value the number to encode.
-
@return the encoded string.
*/
public String encode(BigInteger value) {List<Character> result = new ArrayList<Character>();
BigInteger base = new BigInteger("" + dictionary.length);
int exponent = 1;
BigInteger remaining = value;
while(true){
BigInteger a = base.pow(exponent); //16^1 = 16
BigInteger b = remaining.mod(a); //119 % 16 = 7 | 112 % 256 = 112
BigInteger c = base.pow(exponent - 1);
BigInteger d = b.divide(c);//if d > dictionary.length, we have a problem. but BigInteger doesnt have //a greater than method :-( hope for the best. theoretically, d is always //an index of the dictionary! result.add(dictionary[d.intValue()]); remaining = remaining.subtract(b); //119 - 7 = 112 | 112 - 112 = 0 //finished? if(remaining.equals(BigInteger.ZERO)){ break; } exponent++;}
//need to reverse it, since the start of the list contains the least significant values
StringBuffer sb = new StringBuffer();
for(int i = result.size()-1; i >= 0; i--){
sb.append(result.get(i));
}
return sb.toString();
}
/**
decodes the given string from the base of the dictionary provided in the constructor.
@param str the string to decode.
-
@return the decoded number.
*/
public BigInteger decode(String str) {//reverse it, coz its already reversed!
char[] chars = new char[str.length()];
str.getChars(0, str.length(), chars, 0);char[] chars2 = new char[str.length()];
int i = chars2.length -1;
for(char c : chars){
chars2[i--] = c;
}//for efficiency, make a map
Map<Character, BigInteger> dictMap = new HashMap<Character, BigInteger>();
int j = 0;
for(char c : dictionary){
dictMap.put(c, new BigInteger("" + j++));
}BigInteger bi = BigInteger.ZERO;
BigInteger base = new BigInteger("" + dictionary.length);
int exponent = 0;
for(char c : chars2){
BigInteger a = dictMap.get(c);
BigInteger b = base.pow(exponent).multiply(a);
bi = bi.add(new BigInteger("" + b));
exponent++;
}return bi;
}
- contains hexadecimals 0-F only.
}
