UMBC CMSC 313, Computer Organization & Assembly Language,
Spring 2002, Section 0101
Programming Exercise 2: Base Conversion
Also available in PDF.
Due: Tuesday February 26, 2002
The objective of this programming exercise is to practice designing
your own loops and branching code in assembly language and to gain
greater familiarity with the i386 instructions set.
Write an assembly language program that prompts the user for an
input string, reads the input string and interprets it as an unsigned
number in base 10. Your program must convert the ASCII string
representation of this number into a 32-bit unsigned binary number
and store it in a memory location. Finally, your program must
prepare and store an ASCII string for the hexadecimal representation
of the same number and print it out.
Your program should generate an error if the input string contains
a character that is not 0 through 9 (except for the linefeed at
the end) and if the number does not fit in 32 bits.
Enter Base 10 number: 32767
- The MUL instruction always multiplies something
with the EAX, AX or AL register. The product is stored in EDX:EAX,
DX:AX or AX. So the EDX register might be affected by the MUL
instruction. Also, the MUL instruction does not take an immediate
- The user input has a linefeed character at the end.
You do not want to consider this character when you convert from
base 10 to binary.
- The length of the output string is not the same as
the length of the input string! The ASCII string printed out always
has 8 characters followed by a linefeed (assuming that you print
out leading zeroes).
- You will find the rotate left instruction ROL especially
useful when you prepare an ASCII string for the hexadecimal
representation of a number.
- Note that the character 'A' does not follow the digit
'9' in ASCII. Remember this when you convert the number into a hex
Turning in your program
Use the UNIX script command to record some sample runs of your
program. You should use inputs that result in a variety of hex
string outputs and also inputs that demonstrate the error checking
features of your program. For some of the test cases, use the gdb
debugger to show that the correct number is stored in memory.
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' and the assignment name is 'prog2'. The UNIX command
to do this should look something like:
submit cs313 prog2 convert.asm typescript
8 May 2002 23:36:41 EDT
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