CS 2011, A Term 1999
Prof. Sergio A. Alvarez
Homework 4 (due Sept. 24)


The objective of this assignment is to practice assembly language procedure calls that use the stack for parameter passing. You will need to set up and use a stack frame to access incoming parameters within a recursive function, and you will need to take care of cleaning up the stack after each call.


  1. Write an assembly language procedure named product that receives two singleword unsigned integer parameters x and y by value on the stack and returns the value of the product x*y in register AX (whenever possible, that is; see below for error handling). The product procedure should be thought of as having the functional prototype product(x,y); calling programs should first push x onto the stack, then y, before calling product. Your product procedure should be recursive (calls itself), patterned after the recursive definition   x*(y+1) = x*y + x   together with the base case x*0 = 0.
  2. Write an assembly procedure named main that prompts the user for values of x and y, calls your product procedure to compute x*y, and displays the result to the user. Use DOS function calls or appropriate I/O functions from the Irvine library irvine.lib as in the outline provided in hw4.asm. Source code for all I/O procedures should be placed in one or more files separate from the file containing the main program.
  3. Assemble, link, and debug your program using tasm / tlink / td. Test it on a variety of input pairs (x,y). Note that both arithmetic overflow/carry and stack overflow may occur. Print suitable error messages when such situations arise.


  1. Submit a floppy disk containing all necessary assembly source files and library modules, documentation including complete command line tasm/tlink options (follow the WPI CS documentation standard described at http://www.cs.wpi.edu/Help/documentation-standard.html), and a script file showing the DOS window view of a run of your program (you may use the prn2file utility available on the ccc machines in the directory /cs/cs2011/   to generate the script file).
  2. Give a step-by-step explanation (pictures would be nice, debug information would be fine) of how the stack evolves as your program computes the product 15*4.
  3. Discuss the limitations of your product(x,y) function. Does it return the correct value of x*y for arbitrary unsigned singleword integers x and y? If so, explain in detail. If not, give two examples for which the procedure fails, pointing out what goes wrong in each case.
  4. Submit hardcopies of the above items.
Everything you submit (files too) must include your name, login, and section number.

Background Information

Stack Frames

Refer to recent lectures, and Irvine section 9.3.1.


See Irvine section 5.8.