UMBC CMSC 313, Computer Organization & Assembly Language, Fall 2003

Project 2: Hamming Distance

Due:

Objective

Assignment

"foo" = 0110 0110 0110 1111 0110 1111
"bar" = 0110 0010 0110 0001 0111 0010

Some details:

• Your program must return the Hamming distance of the two strings as the exit status of the program. This is the value stored in the EBX register just before the system call to exit the program.

• To see the exit status of your program, execute the program using the Unix command:

  a.out ; echo $?

• Since the exit status is a value between 0 and 255, you should restrict the user input to 31 characters.

• If the user enters two strings with different lengths, your program should return the Hamming distance up to the length of the shorter string.

• Look up the i386 instructions ADC and XOR and determine how these instructions are relevant to this programming project.

• Record some sample runs of your program using the Unix script command.

Implementation Notes

• The easiest way to examine the contents of a register bit-by-bit is to use successive SHR instruction to shift the least significant bit into the carry flag.

• When you use the gdb debugger to run your program, note that gdb reports the exit status as an octal (base 8) value. The Unix shell reports the exit status in decimal.

• The Hamming distance between the following two strings is 38:

  this is a test
  of the emergency broadcast

  You must also make your own test cases.

• Part of this project is for you to decide which registers should hold which values and whether to use 8-bit, 16-bit or 32-bit registers. A logical plan for the use of registers will make your program easier to code and easier to debug --- i.e., think about this before you start coding.

Turning in your program

Use the UNIX submit command on the GL system to turn in your project. You should submit two files: 1) the modified assembly language program and 2) the typescript file of sample runs of your program. The class name for submit is cs313_0101, cs313_0102 or cs313_0103 for respectively sections 0101 (Chang), 0201 (Patel & Bourner) or 0301 (Macneil). The name of the assignment name is proj2. The UNIX command to do this should look something like: