UMBC CMSC 313, Computer Organization & Assembly Language,
Fall 2002, Section 0101
Project 3: Long Multiplication
Also available in PDF.
Due: Thursday October 10, 2002
The objective of this project is to gain experience writing more
complex assembly language programs.
Write an assembly language program that takes two arbitrarily long
strings from the user. These strings should be interpreted as
unsigned hexadecimal numbers. Your program must then multiply these
two numbers and output the product as a hexadecimal number. The
algorithm you should follow to do this multiplication is the same
long multiplication algorithm you learned in elementary school.
- You will find the code to read in and convert two
arbitrarily long hexadecimal numbers in:
There's also code for printing out long binary numbers.
- Although your code must essentially work for input
numbers of any size, you are allowed to limit the user's inputs
to 64 digit hexadecimal numbers. This is so we do not have to deal
with memory allocation issues, but nevertheless your program should
be able to handle more digits by changing the definition of a single
- It is OK to multiply the numbers byte by byte instead
of 32-bit word by 32-bit word.
- Numbers must be stored in little-endian format.
- You will find the ADC (add with carry) instruction
- Remember that IMUL is for signed numbers, so you must
use MUL instead of IMUL.
- The syntax for a MUL instruction to multiply the AL
register with a memory location is something like:
MUL byte [esi]
The AL register is implicit and must not be specified.
- You may assume that multiplying an n-byte number with
an m-byte number results in an (n+m)-byte product.
- You will need to carefully plan what information is
stored in which registers and what information is stored in
- Complex addressing modes such as [esi + ecx] will come
- You can check your result using dc the "desktop
calculator". Type in 16 o 16 i to put the program in hexadecimal
mode. Note that dc uses Reverse Polish Notation, so adding 5 to 3
is accomplished by
5 3 + p
The final p prints out the result to the screen. Type man dc to
obtain full documentation on dc.
Turning in your program
Use the UNIX script command to record some sample runs of your
program. Your sample runs should thoroughly exercise your program
using inputs that are long enough and complex enough to demonstrate
that your program handles multiple word multiplication correctly.
You should submit two files: 1) your assembly language program and
2) a typescript file of your sample runs. The class name for submit
is "cs313-0101" and the assignment name is "proj3". The UNIX
command to do this should look something like:
submit cs313-0101 proj3 multiply.asm typescript
30 Sep 2002 23:22:29 EDT
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