lseek(fd, off, ptr)int fd, ptr;long off;{	unsigned a;	a = off;	if (a == off)		return (syscall(19, fd, 0, a, ptr, 0));	a = off/512;	syscall(19, fd, 0, a, ptr+3, 0);	return(syscall(19, fd, 0, (int) (off%512), ptr, 0));}