arithmetic.c

自己用C语言编写的一个算术编码的程序

#include<stdio.h>
#include<conio.h>
#include<alloc.h>


FILE *fin;
char *filein;


struct alphabet                /*定义list结构体，alph指定字节，time出现次数 */

               {
                  char alph;         /*记录字母*/
                  double time;          /*记录字母出现次数*/
                  double freq;       /*记录字母出现概率*/
                  double rangelow;
                  double rangehigh;
               };

struct alphabet a[10];

void initiate()
{
  int k;
  a[1].alph=' ';
  a[2].alph='a';
  a[3].alph='b';
  a[4].alph='e';
  a[5].alph='g';
  a[6].alph='i';
  a[7].alph='l';
  a[8].alph='s';
  a[9].alph='t';

  for(k=1;k<=9;k++)
  {
    a[k].time=0;

  }
}

void input()             /*输入文件名，对文件中的每个字节进行计数*/
{
        /* FILE *fin,*fout;   */
         char ch;
         int k;
         double r=0;         /*计算rangelow和rangehigh*/
         double sum=0.0;
         printf("enter the filename of from which the data is to be read::\n");
         scanf("%s",filein);
         fin=fopen(filein,"r");

         while((ch=fgetc(fin))!=EOF)
        {
            switch(ch)
           {
             case ' ':  a[1].time=a[1].time+1;break;
             case 'a':  a[2].time=a[2].time+1;break;
             case 'b':  a[3].time=a[3].time+1;break;
             case 'e':  a[4].time=a[4].time+1;break;
             case 'g':  a[5].time=a[5].time+1;break;
             case 'i':  a[6].time=a[6].time+1;break;
             case 'l':  a[7].time=a[7].time+1;break;
             case 's':  a[8].time=a[8].time+1;break;
             case 't':  a[9].time=a[9].time+1;break;
           }

        }
        for(k=1;k<=9;k++)
        {
          sum=sum+a[k].time;
        }

        for(k=1;k<=9;k++)
        {
          a[k].freq=a[k].time/sum;
        }

        for(k=1;k<=9;k++)
        {
         a[k].rangelow=r;
         a[k].rangehigh=r+a[k].freq;
         r=r+a[k].freq;
        }

        fclose(fin);                         /*关闭文件*/

}

main()
{

  int i;
  double low,high,range,tlow,tag;
  char ch;

  initiate();
  input();

  low=0.0;
  high=1.0;

  fin=fopen(filein,"r");
  while((ch=fgetc(fin))!=EOF)
  {
    range=high-low;
     tlow=low;
     switch(ch)
           {
             case ' ':  low=tlow+range*a[1].rangelow;high=tlow+range*a[1].rangehigh;break;
             case 'a':  low=tlow+range*a[2].rangelow;high=tlow+range*a[2].rangehigh;break;
             case 'b':  low=tlow+range*a[3].rangelow;high=tlow+range*a[3].rangehigh;break;
             case 'e':  low=tlow+range*a[4].rangelow;high=tlow+range*a[4].rangehigh;break;
             case 'g':  low=tlow+range*a[5].rangelow;high=tlow+range*a[5].rangehigh;break;
             case 'i':  low=tlow+range*a[6].rangelow;high=tlow+range*a[6].rangehigh;break;
             case 'l':  low=tlow+range*a[7].rangelow;high=tlow+range*a[7].rangehigh;break;
             case 's':  low=tlow+range*a[8].rangelow;high=tlow+range*a[8].rangehigh;break;
             case 't':  low=tlow+range*a[9].rangelow;high=tlow+range*a[9].rangehigh;break;
           }


   }
/*   while((ch=fgetc(fin))!=EOF)
   printf("%c",ch);    */

   fclose(fin);




  for(i=1;i<=9;i++)
  {
   printf("\nch=%c time=%g freq=%2.1f,rangelow=%2.1f,rangehigh=%2.1f",a[i].alph,a[i].time,a[i].freq,a[i].rangelow,a[i].rangehigh);
  }

  tag=(low+high)/2;

  printf("\nlow=%12.10f   high=%12.10f   tag=%12.10f",low,high,tag);
  getch();
}