Department of Electrical and Computer Engineering
University of Texas at Austin
EE 379K, Fall 2000
Y. N. Patt, Instructor
TAs: Kathy Buchheit, Laura Funderburg, Chandresh Jain, Onur Mutlu,
Danny Nold, Kameswar Subramanian, Francis Tseng, Brian Ward
Programming Assignment 4
Due: November 21, 2000 11:59 PM
Integer to Floating-Point Conversion
In this program we explore how data types can be converted to one another.
We ask you to implement a program in LC-2 assembly language that converts
an integer from its 2's complement representation into its corresponding
floating-point representation and outputs the floating-point equivalent
of the 2's complement integer onto the screen. As the LC-2 does not have
a defined floating-point standard, we will first define a 16-bit floating-point
16-Bit Floating-Point Format Definition
By now, you should be familiar with the 32-bit IEEE standard floating-point
format. If you want to refresh your memory, take a look at section 2.7.1
of the textbook. The word-size of LC-2 is 16 bits. Therefore, to make things
easier we will define a 16-bit floating-point format to be used in this
program. This format consists of 1 sign bit, 6 bits reserved for the exponent,
and 9 bits reserved for the fraction. The format of a floating-point number
looks like the following:
The bias of the above definition is 31, and therefore any floating-point
number in the above format evaluates to
(-1)S x 2(exponent - 31) x 1.fraction
Your program should perform the following steps:
Take a 2's complement number stored in memory location x3100,
convert the number into the floating-point representation specified above,
and store the converted result into memory location x3101. Note
that you will have to set memory location x3100 with a 2's complement
value before you execute your program.
Output the 16-bit floating-point representation in 0's and 1's onto the
For example, suppose memory location x3100 contains the value
(decimal 25) before the program starts. After the program executes, memory
location x3101 should contain the value 0100011100100000
(floating-point 25). The program should also output the following:
FP representation is 0100011100100000
Suppose memory location x3100 contains the value 1000000000000000
(decimal -32768) before the program starts. After the program executes,
memory location x3101 should contain the value 1101110000000000
(floating-point -32768). The program should also output the following:
FP representation is 1101110000000000
You are not required to perform bounds checking. Note that the 2's complement
number in memory location x3100 contains a number in the range
-32768 to 32767.
Store the result of the floating-point conversion in memory location
Make sure you follow the output conventions (i.e. the output should be
exactly the same as the sample output shown above).
Important: When the fraction field is not enough to accurately represent
the initial integer, truncate the fraction field. The floating-point representation
should be as close as possible in value to the initial integer. For example,
if memory location x3100 contains the 2's complement representation
of the integer 4147, the floating-point representation of 4147 should be
0101011000000110. Note that if you calculate what floating-point 0101011000000110
corresponds to, you will get the value of 4144. This is due to the fact
that, to be precisely represented in the above floating-point format, 4147
needs a fraction field of at least 12 bits. But our floating-point format
has a fraction field of 9 bits. Therefore the least significant three bits
in the fraction of 4147 should be discarded. This is called truncation.
Writing and submitting your program
Your code should have a comment block at the beginning of the file. Include
in this comment block, your name, your ECE login name, student number,
and a brief description of the program. Your description should serve as
a general summary of your program's approach to the problem and will aid
in grading. It will also serve as a guideline for assigning partial credit.
It is in your best interest to make all of your ideas clear through this
summary and through commenting within your code.
We request you place your program at starting at memory location x3000.
Think carefully about the design of your program before you start writing
your code. Try to make a flowchart in the beginning.
This program is due before 11:59pm on November 21. Submit your assembly
file using the submit program or the submit script. The program number
Check your ECE email to verify that you have submitted your program correctly.
If you don't get a confirmation, we might not see your submission.