MTF.cpp

/*
 * MTF.cpp
 *
 *  Created on: 18/04/2014
 *      Author: ari
 */

#include "MTF.h"
#include <iostream>
#include <memory.h>

namespace std {


MTF::MTF() {
	// Basado en analisis de frecuencias de enwiki9, pasado a texto plano.
	unsigned short int initial_vector[] = { 32, 101, 111, 116, 110, 105, 97, 114, 115, 104, 108, 100,
				99, 117, 102, 109, 103, 112, 119, 121, 118, 98, 122, 107, 120, 106, 113, 96, 95, 94, 93, 92, 91,
				90, 9, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80, 8, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 7, 69,
				68, 67, 66, 65, 64,	63, 62, 61, 60, 6, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 5, 49,
				48, 47, 46, 45, 44, 43, 42, 41,	40, 4, 39, 38, 37, 36, 35, 34, 33, 31, 30, 3, 29, 28, 27, 26,
				255, 254, 253, 252, 251, 250, 25, 249, 248, 247, 246, 245, 244, 243, 242, 241, 240, 24, 239, 238,
				237, 236, 235, 234, 233, 232, 231, 230, 23, 229, 228, 227, 226, 225, 224, 223, 222, 221, 220, 22,
				219, 218, 217, 216, 215, 214, 213, 212, 211, 210, 21, 209, 208, 207, 206, 205, 204, 203, 202, 201,
				200, 20, 2, 199, 198, 197, 196, 195, 194, 193, 192, 191, 190, 19, 189, 188, 187, 186, 185, 184, 183,
				182, 181, 180, 18, 179,	178, 177, 176, 175, 174, 173, 172, 171, 170, 17, 169, 168, 167, 166, 165,
				164, 163, 162, 161, 160, 16, 159, 158, 157, 156, 155, 154, 153, 152, 151, 150, 15, 149, 148, 147,
				146, 145, 144, 143, 142, 141, 140, 14, 139, 138, 137, 136, 135, 134, 133, 132, 131, 130, 13, 129,
				128, 127, 126, 125, 124,123, 12, 11, 10, 1, 0};
	for(int i=0;i<256;i++){
		this->initial_vector[i] = initial_vector[i];
	}
}

void MTF::resetStatus(){
	// Esto se puede optimizar. SEGURO.
	this->symbol_status.clear();
	for (int i=0; i<256; i++)
		this->symbol_status.push_back(this->initial_vector[i]);
}

void MTF::updateStatus(unsigned char lastpos){
	list<unsigned short int>::iterator it = this->symbol_status.begin();
	unsigned short int elem;

	if (lastpos == 0)
		return;
	advance(it,lastpos);
	elem = *it;
	this->symbol_status.erase(it);

	if (lastpos == 1)
		this->symbol_status.push_front(elem);
	else{
		it = this->symbol_status.begin();
		advance(it,1);
		this->symbol_status.insert(it,elem);
	}
}
unsigned char MTF::getCurrentPosition(unsigned char c){

	list<unsigned short int>::iterator it = this->symbol_status.begin();
	unsigned char pos = 0;
	while(it != this->symbol_status.end()){
		if (*it == c)
			return pos;
	pos++;
	it++;
	}
	return pos;
}


DataBlock * MTF::encode(DataBlock * blockData){

	//unsigned long int resultpos=0;
	DataBlock * result = new DataBlock();
	unsigned char r;
	this->resetStatus();
	vector<unsigned char>::iterator it = blockData->getIterator();
	unsigned long int blockLenght=blockData->getSizeInBytes();
	if(!blockLenght)
		return result;

	//result =(unsigned char *) malloc(blockLenght);
	for (unsigned long int i=0;i<blockLenght;i++){
		//cerr << "MTF: encodeando char# " << i << endl;
		r=this->getCurrentPosition(it[i]);
		result->addByte(r);
		this->updateStatus(r);
		//resultpos++;
	}
	return result;
}

DataBlock * MTF::decode(DataBlock * blockData){
	unsigned long int resultpos=0;
	unsigned long int blockLenght=blockData->getSizeInBytes();
	vector<unsigned char>::iterator it = blockData->getIterator();
	DataBlock * result = new DataBlock();
	this->resetStatus();

	if(!blockLenght)
		return result;

	for (unsigned long int i=0;i<blockLenght;i++){
		result->addByte(this->getElementAt(it[i]));
		//cerr << "ENCODE " << it[i] << " as " << (int)getElementAt(it[i]) << endl;
		this->updateStatus(it[i]);
		//cerr << "NEW POS " << (int)getElementAt(it[i]) << endl;
		resultpos++;
	}
	return result;
}

unsigned char  MTF::getElementAt(unsigned short int position){
	list<unsigned short int>::iterator it = this->symbol_status.begin();
	advance(it,position);
	return *it;
}

MTF::~MTF() {
	this->symbol_status.clear();
}

} /* namespace std */