Fun with Binary Numbers

Here's a question, Say I have a binary number like this 1101 0100 0110 0110 And I want to pull out of the binary number the third quartet (is that the right word) I want to know how to apply the mask 0000 1111 0000 0000 to the number above so that the result would be 0100 Likewise, given the number: 1101 0100 0110 0110 and the mask 0000 0000 1111 0000 the result 0110 I suppose this is the same algorithm used to separate the host from the node address given an IP address and a subnet mask. I just need to know what the algorithm is. Thanks David