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Encoding.java
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Encoding.java
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import java.util.Random;
public abstract class Encoding
{
// Generic Encoding utilities and base class for other encodings
/*
Copyright (C) 2019 S Combes
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program 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
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
protected Codespace cs;
public static Random rand=new Random(); // Insert number for fixed seed - debugging
static String nL = System.getProperty("line.separator");
Encoding() { cs=new Codespace(); }
Encoding(Codespace cs) { this.cs=cs; }
// Does not make a new one - speed, and Codespaces should be invariant
abstract public String encode(String PT);
abstract public String decode(String CT);
// ----------------------------------------------------------------------
public boolean multiTest()
{
boolean result=true;
String [] tests={"THERAININSPAINFALLSMAINLYONTHEPLAIN","ANIMALVEGETABLEORMINERAL",
"ITISAFARFARBETTERTHINGIDOTODAYTHANIHAVEEVERQUITEGOTROUNDTODOINGBEFORE",
"STHISQTIMETHEREWASJUSTTHEDEADEART",
"THISTIMETHEREWOULDBENOWITNESSESSTHISQTIMETHEREWASJUSTTHEDEADEART"};
for (String s : tests)
result&=cycleTest(s);
return result;
}
// ----------------------------------------------------------------------
public boolean cycleTest(String text)
{
String CT=encode(text);
String PT=decode(CT); // Use substring to avoid nulls giving false negs
if (!PT.substring(0,text.length()).equals(cs.flattenToPT(text))) {
System.out.println("*** FAILED cycle test 1 "+nL+PT+nL+cs.flattenToPT(text));
return false;
}
// Do not try in reverse (decode then encode) as some ciphers can't decode
// text not encoded by themselves (e.g. Playfair cannot see paired letters)
return true;
}
// ----------------------------------------------------------------------
public boolean knownTestEncode(String PT,String CT)
{
String text=encode(PT);
if (!CT.equals(text)) {
System.out.println("*** FAILED known test for CT");
System.out.println("Try : "+text);
System.out.println("CT : "+CT);
return false;
}
return true;
}
// ----------------------------------------------------------------------
public boolean knownTestDecode(String PT,String CT)
{
String text=decode(CT);
if (!PT.equals(text)) {
System.out.println("*** FAILED known test for PT");
System.out.println("Try : "+text);
System.out.println("PT : "+PT);
return false;
}
return true;
}
// ----------------------------------------------------------------------
public boolean knownTest(String PT,String CT)
{
boolean pass=knownTestEncode(PT,CT);
reset();
return (knownTestDecode(PT,CT) && pass); // Do in this order, so both tried.
}
// ----------------------------------------------------------------------
public void reset() { return ;} // Dummy to be overridden.
// Reset encodings/ciphers having an internal state to initialisation value
// ----------------------------------------------------------------------
protected long factorial(int n) // Minor utility
{ // Only for fairly small numbers
long result=1;
for (long i=2;i<=n;i++)
result*=i;
return result;
}
// ----------------------------------------------------------------------
public int[] histogram(String text) // Minor utility
{ // Returns histogram of free letters
int [] histogram=new int[cs.PTspace.length()];
for (int i=0;i<text.length();i++)
histogram[cs.PTspace.indexOf(text.charAt(i))]++;
return histogram;
}
// ----------------------------------------------------------------------
public static String reverse(String word) { // Minor utility
return new StringBuilder(word).reverse().toString();
}
// ----------------------------------------------------------------------
public String expand(String text)
{ // Converts/expands CT into full codespace alphabet
// N.B. Uses randomness - only really relevant for ciphers
StringBuilder sb=new StringBuilder("");
for (int i=0;i<text.length();i++) {
int c=cs.CTmap.length()-cs.CTmap.replace(text.substring(i,i+1),"").length();
if (c==1) sb.append(cs.codeSpace.charAt(cs.CTmap.indexOf(text.charAt(i))));
else {
int done=0;
int tgt=rand.nextInt(c);
for (int j=0;j<cs.CTmap.length();j++)
if (cs.CTmap.charAt(j)==text.charAt(i))
if (done++ == tgt)
{ sb.append(cs.codeSpace.charAt(cs.CTmap.indexOf(text.charAt(j)))); break; }
}
}
return sb.toString();
}
// ----------------------------------------------------------------------
public String toString() { return (nL+cs); }
}