Alan And His Magic Field

Alan has a magic field which is divided into $n$x$m$ blocks. That is to say, there are $n$ rows and $m$ columns on the field. Ralph can put an integer in each block. However, the magic field doesn't always work properly. It works only if the product of integers in each row and each column equals to $k$, where $k$ is either $1$ or $-1$. Now Alan wants you to figure out the number of ways to put