UMBC CMSC 313, Computer Organization & Assembly Language,

Programming Exercise 2: Base Conversion

Due: June 17, 2002

Objective

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.

Assignment

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 must continue requesting input from the user, until the user inputs the value zero.

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.

Example:

linux1% a.out Enter Base 10 number: 32767 Original: 32767 Convert: 00007FFF Enter Base 10 number: 0

Implementation Issues:

  1. 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 operand.
  2. 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.
  3. 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).
  4. You will find the rotate left instruction ROL especially useful when you prepare an ASCII string for the hexadecimal representation of a number.
  5. Note that the character 'A' does not follow the digit '9' in ASCII. Remember this when you convert the number into a hex string.

Turning in your program

You should submit two files:1) your assembly language program and 2) a typescript file of your sample runs.
email your programs to burt@cs.umbc.edu