CS 2011, A Term 1999
Prof. Sergio A. Alvarez
Lab 5


The goal of this lab is for you to implement and test a linear congruence pseudorandom number generator. Pseudorandom number generators have many uses, such as stochastic system simulation and encryption as in HW 5. This lab requires linking multiple modules together and handling procedure calls using stack parameters.


  1. Insert a floppy disk. Open a DOS window on your PC. At the DOS prompt, type "cd A:\" (no quotes) to change the directory to the floppy drive. Download the 80X86 assembly language source file randgen.asm onto your floppy disk, to a file named A:\randgen.asm. This file contains the outline of a procedure named rando which accepts an incoming seed value on the stack and returns a corresponding pseudorandom number in register DX.
  2. Using a text editor (for example the DOS edit command), edit randgen.asm, adding any necessary directives, including a public directive for the rando procedure, and code to set up a stack frame, retrieve the incoming seed value and place it in the appropriate register, dismantle the stack frame, and return, appropriately clearing the stack. See the statement of HW 5 for information about the linear congruence method being used here. Assemble randgen.asm using the command tasm/la/zi randgen.asm.
  3. Place your copy of the Irvine link library irvine.lib in the A:\ directory. If you didn't bring your copy, you may download one in zipped form from Irvine's site at http://www.nuvisionmiami.com/books/asm/. Be sure to unzip it before attempting to use it. Ask the TA if you need help.
  4. Write a separate module mainprog.asm that prompts the user to input a seed value and a count value, calls rando count-many times with the user-specified seed value as initial input, and prints the pseudorandom number sequence returned by rando on the console in decimal notation. Remember to push the appropriate seed value onto the stack before each call to rando; use the pseudorandom value output by rando as the next seed value. For I/O, use the Irvine library functions Writestring, Readint, and Writeint. Include suitable extrn declarations. The following descriptions are from section 4.7 of the textbook:
  5. Assemble the file mainprog.asm using the command tasm/la/zi mainprog.asm, and link the object files mainprog.obj and randgen.obj with the Irvine library irvine.lib using the command line tlink/3/m/v mainprog.obj randgen.obj irvine.lib. To speed up the assembly and linking process, you may place the above full sequence of tasm and tlink commands (for both randgen and mainprog) together in a batch file named randlink.bat and then simply type randlink at the DOS prompt.
  6. Run the resulting executable file mainprog.exe by typing mainprog at the DOS prompt. Test your program for several input values. Can you see any clear patterns in the output sequences?
  7. If you'd like, use any remaining time to continue working on HW 5.
  8. When you're done, remove your floppy disk from the drive and return the computer to a state in which other students will be able to make full use of it (in case of doubt, ask your TA).
  9. Make sure you've signed the TA's sign-in sheet.