I wasn't aware that DOS has an in-built calculator in it till yesterday morning. Ok based on my understaning I have written the following ... hope this info would be of some help to you!!
DOS Shell has a built in mini calculator to perform mathematical calculation.
Syntax for SET command: Set /a Your_Expression_Comes_here
As you would be knowing, type set /? to display the complete help of that command. Btw, this supports "SHIFT" operators (both left <<>>).
Try it yourself:
Step1: Open the command prompt (Start >> Run >> cmd)
Step 2: Find below the screenshot which shows few examples I have tried myself.