LZW就是通过建立一个字符串表，用较短的代码来表示较长的字符串来实现压缩。
压缩算法如下
#include <iostream>
#include <fstream>
std::ifstream fin;
std::ofstream fout;
using namespace std;
const int D = 4096,
alpha = 256,
ByteSize = 8,
HalfByte = 4,
AllBit = 255,
HalfBit = 15;
int used, state = 0;
char LastChar, LeftHalf;
unsigned long outch;
struct
{
long int code;
}ht[D];
bool search(long int cd, int& tk)
{
for (int i = 0; i < used; i++)
if (ht[i].code == cd)
{
tk = i;
return true;
}
return false;
}
bool openfile()
{
fin.open("123.txt", std::ios_base::binary);
fout.open("123.lzw", std::ios_base::binary | std::ios_base::out);
if (fin.fail() || fout.fail())
return false;
else
return true;
}
void output(long val)
{
unsigned char ch, ck;
if (state)
{
ch = (val >> ByteSize & HalfBit) | (LeftHalf << HalfByte);
ck = val & AllBit;
fout.put(ch);
fout.put(ck);
state = 0;
}
else
{
ch = val >> HalfByte;
fout.put(ch);
LeftHalf = val & HalfBit;
state = 1;
}
}
void compress()
{
int i;
for (i = 0; i < alpha; i++) //用256个字符进行初始化
ht[i].code = i;
used = alpha; //已使用
char ch;
unsigned long cd, pcode;
int tk;
fin.get(ch);
pcode = ch;
while(!fin.eof())
{
fin.get(ch);
cd = (pcode << ByteSize) + (unsigned char)ch;
if (fin.eof())
{
//break;
}
if (search(cd, tk))
{
pcode = tk;
}
else
{
output(pcode);
if (used < D)
{
ht[used].code = (pcode << ByteSize | ((unsigned)ch));
used++;
}
pcode = ch;
}
}
output(pcode);
if (state)
{
cout <<"error\n";
ch = LeftHalf << HalfByte;
fout.put(ch);
}
}
int main()
{
if (openfile())
cout <<"file ready!\n";
compress();
cout <<"ok\n";
int i;
/*
for (i = 0; i < 256; i++)
cout <<i <<"\t"<< ht[i].key <<"\t" <<char(ht[i].code) <<endl;
*/
for (i = 256; i < used; i++)
//cout <<i <<"\t" <<(ht[i].code>>8) <<" "<<char(ht[(ht[i].code>>8)].code)<<" "<<char(ht[i].code & AllBit) <<endl;
fin.close();
fout.close();
return 0;
}
解压算法如下
hashlist.h
/********************************************************************
purpose: 链表散列
author: xianyun1230
QQ: 836663997
e-mail: xianyun1230@163.com
created: 2014/02/23
*********************************************************************/
template<typename K, typename T>
class hashlist
{
public:
hashlist(int num);
~hashlist();
bool search(const K k, T& val);
bool insert(const K k, T val);
bool del(const K k);
void show()const;
private:
typedef struct _node
{
K key;
T data;
struct _node *next;
}node;
node* hsearch(K k);
int D;
node **lst;
};
template<typename K, typename T>
hashlist<K,T>::hashlist(int num)
{
D = num;
lst = new node *[D];
for (int i = 0; i < D; i++)
{
lst[i] = new node;
lst[i]->next = NULL;
}
}
template<typename K, typename T>
hashlist<K,T>::~hashlist()
{
node *tmp, *ph;
for (int i = 0; i < D; ++i)
{
tmp = lst[i]->next;
while (tmp)
{
ph = tmp->next;
delete tmp;
tmp = ph;
}
delete lst[i];
}
delete lst;
}
template<typename K, typename T>
hashlist<K,T>::node* hashlist<K,T>::hsearch(K k)
{
node *tmp = lst[k % D];
while(tmp->next)
{
if (tmp->next->key == k)
return tmp;
tmp = tmp->next;
}
return tmp;
}
template<typename K, typename T>
bool hashlist<K,T>::search(const K k, T& val)
{
node* pt = hsearch(k);
if (pt->next == NULL)
return false;
if (pt->next->key == k)
{
val = pt->next->data;
return true;
}
else
return false;
}
template<typename K, typename T>
bool hashlist<K,T>::insert(const K k,T val)
{
node* pt = hsearch(k);
if (pt)
{
node* tmp = new node;
tmp->key = k;
tmp->data = val;
tmp->next = pt->next;
pt->next = tmp;
return true;
}
return false;
}
template<typename K, typename T>
bool hashlist<K,T>::del(const K k)
{
node* pt = hsearch(k);
if (pt->next != NULL)
{
node* tmp = pt->next;
pt->next = tmp->next;
delete tmp;
if (pt == lst[k%D])
pt->next = NULL;
return true;
}
return false;
}
template<typename K, typename T>
void hashlist<K,T>::show() const
{
node* tmp;
for (int i = 0; i < D; ++i)
{
tmp = lst[i]->next;
while (tmp)
{
std::cout <<tmp->data <<" ";
tmp = tmp->next;
}
}
std::cout <<std::endl;
}
main.cpp
#include <iostream>
#include <fstream>
#include "hashlist.h"
std::ifstream fin;
std::ofstream fout;
const int D = 4096,
alpha = 256,
ByteSize = 8,
HalfByte = 4,
AllBit = 255,
HalfBit = 15;
int used, state = 0;
char LastChar, LeftHalf;
unsigned long outch;
char s[D];
int slen;
struct
{
int pre;
char ch;
}ht[D];
bool openfile()
{
fin.open("123.lzw", std::ios_base::binary);
fout.open("123-lzw.txt", std::ios_base::binary | std::ios_base::out);
if (fin.fail() || fout.fail())
return false;
else
return true;
}
bool getcode(int &code)
{
char tch, tck;
unsigned char ch, ck;
fin.get(tch);
ch = tch;
if (fin.eof())
return false;
code = ch;
if (state)
{
code = (LeftHalf << ByteSize) | ch;
state = 0;
}
else
{
fin.get(tck);
//if (fin.eof())
// return false;
ck = tck;
code = (code << HalfByte) | (ck >> HalfByte);
LeftHalf = ck & HalfBit;
state = 1;
}
return true;
}
void output(int code)
{
slen = -1;
while (code >= alpha)
{
s[++slen] = ht[code].ch;
code = ht[code].pre;
}
s[++slen] = code;
for (int i = slen; i >= 0; --i)
fout.put(s[i]);
}
void decompress()
{
int i, pcode, ccode;
for (i = 0; i < alpha; i++) //用256个字符进行初始化
ht[i].ch = i;
used = alpha; //已使用
if (getcode(pcode))
{
s[0] = pcode;
fout.put(s[0]);
slen = 0;
while (getcode(ccode))
{
if (ccode < used)
{
output(ccode);
if (ccode < D)
{
ht[used].pre = pcode;
ht[used].ch = s[slen];
used++;
}
}
else
{
ht[used].pre = pcode;
ht[used].ch = s[slen];
used++;
output(ccode);
}
pcode = ccode;
}
}
}
int main()
{
using namespace std;
if (openfile())
cout <<"file ready!\n";
decompress();
cout <<"ok\n";
for (int i = 0; i < used; i++)
cout <<i <<"\t"<< ht[i].pre <<" "<<ht[ht[i].pre].ch<<" " <<ht[i].ch <<endl;
fin.close();
fout.close();
return 0;
}
原文地址：http://blog.csdn.net/xianyun2009/article/details/39290871
