linux上用c实现算术编码（二）--具体代码

转载注明出处：http://blog.youkuaiyun.com/wang_zheng_kai

让学生用开发工具，练习学到的数据压缩编码

本文包括两部分：

linux上用c实现算术编码（一）--具体操作

linux上用c实现算术编码（二）--具体代码

/*********************************
***Arithmetic coding fixed mode***
*****Writed By Wang Zhengkai******
***********2014.11.24*************
**********************************/


#include<stdio.h>
#include<math.h>
#include<string.h>

char c[20],s[100];
float p[20],f[20],len;
int cord[100];

/**************************************
 * **************encord****************
 * ***********************************/
void encord(int a,int h)
{
	float Fr;
	float Ps=1;
	float Fs=0;
	float cp[100];
	int i,j;

	for(i=0;i<h;i++)
	{
		for(j=0;j<a;j++)
		{
			if(s[i]==c[j])
			{
				cp[i]=p[j];
				Fr=f[j];
			}		
		}
	Fs=Fs+Ps*Fr;
 	Ps*=cp[i];
	}

	printf("The result of encord: %f\n",Fs);
	
	len=log(1/Ps)/log(2);
	if(len>(int)len) 
		len=(int)len+1;
	else 
		len=(int)len;

	for(i=0;len>i;i++)
	{
		Fs=2*Fs;
		if(Fs>1)
		{
			Fs=Fs-1;
			cord[i]=1;
		}
		else 
			if(Fs<1)
				cord[i]=0;
			else 
			{
				cord[i]=1;
				break;
			}
	}

	if(i>=len)
	{
		for(j=i;j>=1;j--)
		{		
			cord[j-1]=(cord[j-1]+1)%2;
			if(cord[j-1]==1)
				break;	
		}
	}
	
	printf("The resault of encord:\n");
	for(j=0;j<i;j++)
		printf("%d ",cord[j]);
	printf("\n");
}
/**************************************
 * **************decord****************
 * ***********************************/
void decord(int a,int h)
{
	int i,j;
	float Ft,Pt,w=0.5,result=0;
	float Fs=0,Ps=1;
	
	for(i=0;i<len;i++,w*=0.5)  //two_to_ten
		result += w*cord[i];
	printf("Select the number of decode: %f\n",result);

	printf("The result of decord:\n");
	for(i=0;i<h;i++)
	{
		for(j=a;j>0;j--)
		{
			Ft=Fs;
			Pt=Ps;
         		Ft+=Pt*f[j-1];		
			Pt*=p[j-1];	
			if(result>=Ft)
			{
				Fs=Ft;
				Ps=Pt;
				printf("%c ",c[j-1]);
				break;
			}
		}
	}
	printf("\n");
}

int main(void)
{
	int num,i,h=0;
	char rub;

/**************************************
 * ****input num of symbols************
 * ***********************************/
	printf("Please input num of character!\n");
	if(1==scanf("%d", &num))
	{
//		printf("%d\n",num);
		rub=getchar();
	}
	else
	{
		rewind(stdin);
		printf("num:input error!\n");
	}

/**************************************
 * ***input sybmol and values**********
 * ***********************************/
	printf("Please input character symbols and their probability values of corresponding!\n");
	for(i=0;i<num;i++)
	{
		printf("Please input character symbols!\n");
		scanf("%c", &c[i]);
		printf("Please input probability values of corresponding!\n");
		scanf("%f", &p[i]);
		rub=getchar();
	}

	for(i=0;i<num;i++)
	{
		printf("<%d>----> %c   ",i,c[i]);
	}
	printf("\n");
	for(i=0;i<num;i++)
	{
		printf("<%d>----> %f   ",i,p[i]);
	}
	printf("\n");
	
	for(i=1;i<num;i++)
	{
		f[0]=0;
		f[i]=f[i-1]+p[i-1];
	}

/**************************************
 * ******input encord symbol***********
 * ***********************************/
	printf("Please input encord symbols,and input * to exit!\n");
	while(1)
	{
		char ss;
		scanf("%c", &ss);
		rub=getchar();
		if(ss=='*')break;
		s[h++]=ss;
	}
	printf("The numbers of input\n");
	for(i=0;i<h;i++)
	{
	    printf("%c ",s[i]);
	}
	printf("\n");

/**************************************
 * *******encord and dedord************
 * ***********************************/
	printf("............encord............\n ");
  	encord(num,h);
	printf("............decord............\n ");
	decord(num,h);
	return 0;
}