求大神！这是一个简单的C语言加密程序！求解密程序？？

#include <stdio.h>
#include <stdlib.h>
void main()
{ FILE *fp1,*fp2;
char ch;
int i;
if((fp1=fopen("c:\\a.txt","r"))==NULL)
{ printf("fp1 open error!");
getchar();
exit(0);
}
if((fp2=fopen("c:\\b.txt","w"))==NULL)
{ printf("fp2 open error!");
getchar();
exit(0);
} i=0;
while(!feof(fp1))
{ fscanf(fp1,"%c",&ch);
if(ch!=EOF)
{if(ch==' '||ch=='\n')
fprintf(fp2,"%c",ch);
else if( i%2==0)
fprintf(fp2,"%c",ch^4); else if( i%2==1)
fprintf(fp2,"%c",ch<<1);
i++;
}
}
fclose( fp1);
fclose(fp2);
}