XOR Arguments

/*
 * This work is hereby released into the Public Domain.
 */
 
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/stat.h>
 
#define XORBYTE (0x8dUL)
#define XORINT  (XORBYTE | (XORBYTE << 8) | (XORBYTE << 16) | (XORBYTE << 24))
#ifdef __LP64__
  #define XORLONG ((XORINT) | ((XORINT) << 32))
  #define LONG2 3
#else
  #define XORLONG XORINT
  #define LONG2 2
#endif
#define BUFSIZE (2048 << 10)
 
#ifdef WIN32
  #define MODE  (S_IRUSR | S_IWUSR)
#else   
  #define MODE  (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH)
  #define O_BINARY  0
#endif
 
int main(int argc, char *argv[])
{
  unsigned long *buf;
  int i, r, fin, fout;
  fin = open(argv[1], O_RDONLY | O_BINARY);
  fout = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC | O_BINARY, MODE);
  buf = malloc((BUFSIZE >> LONG2) * sizeof(long));
  while ((r = read(fin, buf, BUFSIZE)) > 0) {
    for (i = 0; i < ((r + sizeof(long) - 1) >> LONG2); i++)
      buf[i] ^= XORLONG;
    write(fout, buf, r);
  }
  free(buf);
  close(fout);
  close(fin);
  return 0;
}