/* Invert byte order within each 32-bits of an array.  */
FourByteSwap(unsigned char *buf, size_t nbytes)
/* Invert byte order within each 32-bits of an array.  */
FourByteSwap(unsigned char *buf, size_t nbytes)
{
    for ( ; nbytes >= 4; nbytes -= 4, buf += 4 )
    {
      unsigned char  c;
      c      = buf[0];
      buf[0] = buf[3];
      buf[3] = c;
      c      = buf[1];
      buf[1] = buf[2];
      buf[2] = c;
    }
  }