/* fcrypt program sample solution */

#include<stdio.h>
//#include <sys/types.h>
//#include <sys/stat.h>
#include <fcntl.h>

#define FMSIZE 2048

// make sure at least size elements are read; lseek to start if needed
void alignread(int fd,char *buffer,int size)
  {  int result;
     int boffset;
     result = 0;
     boffset = (int) buffer;
     while (result < size) 
       {     
	 size = size - result;  // # of bytes left to be read
         boffset = boffset + result;  // set buffer offset
	 result = read(fd,(char *)boffset,size);
	 if (result < size) lseek(fd,0,0);  // back to start of file
       } // while loop
  } //  alignread

void bxor(char* b1, char* b2, char* b3, int size)
{ int i;
  for(i=0;i<size;i++)
     b3[i] = b1[i] ^ b2[i];
}


int main(int argc, char *argv[])
{ 
  int infd, outfd, keyfd;  // file descriptors
  int result1;
  char buffer1[FMSIZE];  
  char buffer2[FMSIZE];  
  char buffer3[FMSIZE];  
  FILE *instream;
  FILE *outstream;  


  if (argc != 4) { perror("need 3 args\n"); exit(1); }

  infd = open(*++argv,O_RDONLY,0);
  keyfd = open(*++argv,O_RDONLY,0);
  outfd = creat(*++argv,0755);   // OR_RDWR, O_APPEND, 
  /*

  instream = fdopen(infd, "r");
  outstream = fdopen(dup(infd), "w");

  fprinf(outstream,"dfss");  // now ok
  */

  result1 = 1;
  while (result1 > 0) 
    {
      result1 = read(infd,buffer1,FMSIZE);
      if (result1 > 0) 
	{
	  alignread(keyfd,buffer2,result1);
          bxor(buffer1,buffer2,buffer3,result1);
          write(outfd,buffer3,result1);
	} // if result1>0
    } // while

  close(infd);
  close(keyfd);
  close(outfd);

  exit(0);
} //main