Assignment 1: Othello in MIPS

version: 1.1 last updated: 2022-03-13 01:00:00

Aims

  • to give you experience writing MIPS assembly code
  • to give you experience translating C to MIPS
  • to give you experience with data and control structures in MIPS

Getting Started

Create a new directory for this assignment called othello, change to this directory, and fetch the provided code by running these commands: 

mkdir -m 700 othello
cd othello
1521 fetch othello

If you're not working at CSE, you can download the provided files as a zip file or a tar file.

This will add the following files into the directory:

  • othello.s: a stub MIPS assembly file to complete.
  • othello.c: a reference implementation of Othello in C.
  • othello_EOF.c: additional C file for testing.
  • input.txt: example input file.

Othello: The Game

1521 mipsy othello.s
Welcome to Reversi!
How big do you want the board to be? 8
OK, the board size is 8

It is black's turn.
Board:
   A B C D E F G H 
 1 . . . . . . . . 
 2 . . . . . . . . 
 3 . . . x . . . . 
 4 . . x W B . . . 
 5 . . . B W x . . 
 6 . . . . x . . . 
 7 . . . . . . . . 
 8 . . . . . . . . 
Enter move (e.g. A 1): F 5
It is white's turn.
Board:
   A B C D E F G H 
 1 . . . . . . . . 
 2 . . . . . . . . 
 3 . . . . . . . . 
 4 . . . W B x . . 
 5 . . . B B B . . 
 6 . . . x . x . . 
 7 . . . . . . . . 
 8 . . . . . . . . 
Enter move (e.g. A 1): 
-- CUT --

othello.c is an implementation of Othello, a variant of the classic board game Reversi.

An example game of Othello can be seen to the right.

A game of Othello takes place over a number of turns, as two players battle it out to capture their opponent's pieces!

Each turn, you are allowed to place a piece of your colour (either black or white) in any position (marked with an x) which will capture at least one piece from the opposite player. Capturing occurs when there is a continuous line (vertical, horizontal or diagonal) of your opponent's pieces between your newly placed piece and an existing piece of your colour. Then all of your opponent's pieces in that line are converted to your pieces.

If one player has no legal moves, they forfeit their turn. If neither player has a legal move then the game ends, and whoever has the most pieces on the board wins. The number of empty pieces is added to the winner's total to determine the final score.

To get a feel for this game, try it out in a terminal: 

dcc othello_EOF.c -o othello
./othello

You should read through othello.c. There are comments throughout it that should help you understand what the program is doing [citation needed] — which you'll need for the next part of the assignment.

othello.s: The Assignment

Your task in this assignment is to implement othello.s in MIPS assembly.

You have been provided with some assembly and some helpful information in othello.s. Read through the provided code carefully, then add MIPS assembly so it executes exactly the same as othello.c.

The function print_board has already been translated to MIPS assembly for you.

You have to implement the following functions in MIPS assembly:

  • main,
  • read_board_size,
  • initialise_board,
  • place_initial_pieces,
  • play_game,
  • announce_winner,
  • count_discs,
  • play_turn,
  • place_move,
  • player_has_a_valid_move,
  • is_valid_move,
  • capture_amount_from_direction,
  • other_player,
  • current_player_str.

You must translate each function separately to MIPS assembler, following the standard calling conventions used in lectures. When translating a function, you must not make any assumptions about the behaviour or side effects of any other function which is called.

To run your MIPS code, simply enter the following in your terminal: 

1521 mipsy othello.s

To test your implementation, you can compile the provided C implementation, run it to collect the expected output, run your assembly implementation to collect observed output, and then compare them — for example:

The game takes a lot of input, so it's a good idea to write a file with the input you want to test, then pipe that into your program.

You have been given a file called input.txt as an example. 

dcc othello.c -o othello
cat input.txt | ./othello | tee c.out
cat input.txt | 1521 mipsy othello.s | tee mips.out
diff -s c.out mips.out
Files c.out and mips.out are identical

Try this for different sequences of inputs.

Each function is worth some amount of marks:

Function Mark
main 1
read_board_size 5
initialise_board 4
place_initial_pieces 3
play_game 2
announce_winner 4
count_discs 5
play_turn 7
place_move 6
player_has_a_valid_move 5
is_valid_move 4
capture_amount_from_direction 5
other_player 2
current_player_str 2

These marks represent relative difficulty.

E.g. main may not be worth exactly 1 mark, but will be worth half the marks of play_game.

Hints

  • Functions are not in order of difficulty.

  • You may find it easier to implement the smaller functions before moving on to the larger ones.

  • The C code defines constants using #define, e.g.: 

    #define PLAYER_EMPTY 0
#define PLAYER_BLACK 1
#define PLAYER_WHITE 2

    You can also define constants in mipsy but syntax is a different: 

    PLAYER_EMPTY = 0
PLAYER_BLACK = 1
PLAYER_WHITE = 2

  • You may find the discussion of the assignment during this lecture helpful.

  • You may find the provided print_board function implementation to be useful guidance for your implementations including comments, label names, indentation and register usage.

Simplified C code

You are encouraged to simplify your C code to remove any loop constructs and if-else statements, and testing that your simplified code works correctly before translating it to MIPS, in a separate file othello.simple.c.

This file will not be marked. And you will not need to submit it.

In order to allow you to ensure that your simplified code works correctly, we have provided a series of automated tests.

You can run these tests by running the following command: 

1521 autotest othello.simple

Assumptions, Clarifications, and Restrictions

  • Like all good programmers, you should make as few assumptions as possible.

  • Your submitted code must be hand-written MIPS assembly, which you yourself have written.
    You may not submit code in other languages.
    You may not submit compiled output.

  • You may not copy a solution from an online source.
    e.g. Github.

  • Your functions will be tested individually.
    They must match the behaviour of the corresponding C function and they must follow MIPS calling conventions.

  • There will be a correctness penalty for assignments that do not follow standard MIPS calling conventions including:

    • Function arguments are passed in registers $a0..$a3.

    • Function return values are passed in register $v0

    • Values in registers $s0..$s7 are preserved across function calls.
      If a function changes these registers, it must restore the original value before returning.

    • The only registers' values that can be relied upon across a function call are $s0..$s7, $gp, $sp, and $fp.
      All other registers must be assumed to be have, an undefined value after a function call, except $v0 which has the function return value.

  • If you need clarification on what you can and cannot use or do for this assignment, ask in the class forum.

  • You are required to submit intermediate versions of your assignment. See below for details.

Change Log

Version 1.0
(2022-03-06 12:00:00)
  • Initial release
Version 1.1
(2022-03-13 01:00:00)
  • Remove automatic whitespace trimming from input

Assessment

Testing

We have provided some automated tests to help you check the correctness of your translation. To run all the provided tests, execute the following command: 
1521 autotest othello
Some of these tests check only a specific function, and some test your whole program. To run run all the tests for a specific function, pass the name of the function to autotest. For example, to run all the tests for the main function, run the command: 
1521 autotest othello main
To run the autotests which test your program as a whole, run the command: 
1521 autotest othello whole_prog

Submission

When you are finished working on the assignment, you must submit your work by running give: 

give cs1521 ass1_othello othello.s

You must run give before Week 7 Monday 11:59:59 (midday) to obtain the marks for this assignment. Note that this is an individual exercise, the work you submit with give must be entirely your own.

You can run give multiple times.
Only your last submission will be marked.

If you are working at home, you may find it more convenient to upload your work via give's web interface.

You cannot obtain marks by emailing your code to tutors or lecturers.

You can check your latest submission on CSE servers with: 

1521 classrun check ass1_othello

You can check the files you have submitted here.

Manual marking will be done by your tutor, who will mark for style and readability, as described in the Assessment section below. After your tutor has assessed your work, you can view your results here; The resulting mark will also be available via give's web interface.

Due Date

This assignment is due Week 7 Monday 11:59:59 (midday) (2023-03-27 11:59:00).

The UNSW standard late penalty for assessment is 5% per day for 5 days - this is implemented hourly for this assignment.

Your assignment mark will be reduced by 0.2% for each hour (or part thereof) late past the submission deadline.

For example, if an assignment worth 60% was submitted half an hour late, it would be awarded 59.8%, whereas if it was submitted past 10 hours late, it would be awarded 57.8%.

Beware - submissions 5 or more days late will receive zero marks. This again is the UNSW standard assessment policy.

Assessment Scheme

This assignment will contribute 15 marks to your final COMP1521 mark.

80% of the marks for assignment 1 will come from the performance of your code on a large series of tests.

20% of the marks for assignment 1 will come from hand marking. These marks will be awarded on the basis of clarity, commenting, elegance and style. In other words, you will be assessed on how easy it is for a human to read and understand your program.

An indicative assessment scheme for performance follows.
The lecturer may vary the assessment scheme after inspecting the assignment submissions, but it is likely to be broadly similar to the following:

100% for performance implements all behaviours perfectly,
following the spec exactly.
90% for performance implements all behaviours perfectly,
but doesn't conform to the MIPS ABI
75% for performance implements all simple and
all moderate difficulty functions correctly.
65% for performance implements all simple and
some moderate difficulty functions correctly.
≤ 50% for performance good progress,
simple functions work correctly.

An indicative assessment scheme for style follows.
The lecturer may vary the assessment scheme after inspecting the assignment submissions, but it is likely to be broadly similar to the following:

100% for style perfect style
90% for style great style, almost all style characteristics perfect.
80% for style good style, one or two style characteristics not well done.
70% for style good style, a few style characteristics not well done.
60% for style ok style, an attempt at most style characteristics.
≤ 50% for style an attempt at style.

An indicative style rubric follows.
The lecturer may vary the assessment scheme after inspecting the assignment submissions, but it is likely to be broadly similar to the following:

  • Formatting (8/20):
    • Whitespace
    • Indentation (consistent, tabs or spaces are okay)
    • Line length (below 120 characters unless very exceptional)
    • Line breaks (using vertical whitespace to improve readability)
  • Documentation (12/20):
    • Header comment (with name, zID, description of program)
    • Function comments (above each function with a description)
    • Sensible commenting throughout the code

Note that the following penalties apply to your total mark for plagiarism:

0 for
assignment 1		 knowingly providing your work to anyone
and it is subsequently submitted (by anyone).
0 FL for
COMP1521		 submitting any other person's work; this includes joint work.
academic
misconduct		 submitting another person's work without their consent;
paying another person to do work for you.

Intermediate Versions of Work

You are required to submit intermediate versions of your assignment.

Every time you work on the assignment and make some progress you should copy your work to your CSE account and submit it using the give command below. It is fine if intermediate versions do not compile or otherwise fail submission tests. Only the final submitted version of your assignment will be marked.

Assignment Conditions

  • Joint work is not permitted on this assignment.

    This is an individual assignment. The work you submit must be entirely your own work: submission of work even partly written by any other person is not permitted.

    Do not request help from anyone other than the teaching staff of COMP1521 — for example, in the course forum, or in help sessions.

    Do not post your assignment code to the course forum. The teaching staff can view code you have recently submitted with give, or recently autotested.

    Assignment submissions are routinely examined both automatically and manually for work written by others.

    Rationale: this assignment is designed to develop the individual skills needed to produce an entire working program. Using code written by, or taken from, other people will stop you learning these skills. Other CSE courses focus on skills needed for working in a team.

  • The use of code-synthesis tools, such as GitHub Copilot, ChatGPT, Google Bard, etc. are not permitted on this assignment.

    Rationale: this assignment is designed to develop your understanding of basic concepts. Using synthesis tools will stop you learning these fundamental concepts, which will significantly impact your ability to complete future courses.

  • Sharing, publishing, or distributing your assignment work is not permitted.

    Do not provide or show your assignment work to any other person, other than the teaching staff of COMP1521. For example, do not message your work to friends.

    Do not publish your assignment code via the Internet. For example, do not place your assignment in a public GitHub repository.

    Rationale: by publishing or sharing your work, you are facilitating other students using your work. If other students find your assignment work and submit part or all of it as their own work, you may become involved in an academic integrity investigation.

  • Sharing, publishing, or distributing your assignment work after the completion of COMP1521 is not permitted.

    For example, do not place your assignment in a public GitHub repository after this offering of COMP1521 is over.

    Rationale: COMP1521 may reuse assignment themes covering similar concepts and content. If students in future terms find your assignment work and submit part or all of it as their own work, you may become involved in an academic integrity investigation.

Violation of any of the above conditions may result in an academic integrity investigation, with possible penalties up to and including a mark of 0 in COMP1521, and exclusion from future studies at UNSW. For more information, read the UNSW Student Code, or contact the course account.