Programming 2 (SS 2023)
Saarland University
Faculty MI
Compiler Design Lab
Preparation
To be able to edit the project in Mars, you first have to checkout the repository and import the project:
1. Clone the project in any folder：
where $NAME has to be replaced with your CMS username.
2. Open the cloned directory in Mars.
Check that the settings Assemble all files in directory and Initialize Program Counter to global ‘main’ if defined
in the Settings menu in MARS are activated to compile the file src/main.asm and set the program entry point to
the label main.
In the following document, we refer to the term character as a single byte encoding of a character according to the
ASCII standard. The IBANs only contain ASCII upper case letters and digits. The KNRs and the BLZs consist of
ASCII digits only.
IBAN-Calculator (10 Points)
D E P P B B B B B B B B K K K K K K K K K K
Country code
Check digits
BLZ
KNR
In this project, you will implement an IBAN calculator that converts a bank account number (KNR) and a bank
code (BLZ) to a German IBAN according to the format shown above, or extracts the KNR and the BLZ from a
German IBAN. You can find a general introduction to IBANs in the Wikipedia (https://en.wikipedia.org/
wiki/International_Bank_Account_Number).
You will write the program in MIPS assembler. To make the project easier to handle, it is divided into several
tasks. Each task has its own file in which you will write the corresponding subroutine. Please also pay attention to
the hints at the end of the project description.
1 Extract BLZ and KNR (2 Points)
Write a subroutine iban2knr (file src/iban2knr.asm), which extracts the BLZ and the KNR from a German
IBAN. Your subroutine receives the following arguments:
1. A buffer with a German IBAN with 22 characters.
2. The target buffer for the BLZ with space for 8 characters.
3. The target buffer for the KNR with space for 10 characters.
2 Remainder calculation (4 Points)
Write a subroutine modulo_str (file src/moduloStr.asm), which calculates the remainder of a number given
as a string. Your subroutine receives the following arguments:
1. A buffer with a number.
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2. The length of the number in the buffer.
3. The divisor.
The result is returned in the return register. The number in the buffer is the remainder of the division of the number
represented in the buffer by the divisor. The number in the buffer is a decimal number greater than zero represented
as a string of digits and has no sign. The least significant digit of the number is at position 𝑙𝑒𝑛𝑔𝑡ℎ− 1 in the buffer.
We advise you to calculate the result digit by digit according to the Hornerschema. Take care that the result is also
correct if the number represented in the buffer exceeds the capacity of the machine registers. This can be achieved
by clever use of the following equations (𝑥 mod 𝑦 is the remainder of the division of 𝑥 by 𝑦):
(𝑎 + 𝑏) mod 𝑐 = (𝑎 + (𝑏 mod 𝑐)) mod 𝑐
(𝑎 × 𝑏) mod 𝑐 = (𝑎 × (𝑏 mod 𝑐)) mod 𝑐
You can also reduce intermediate results modulo the divisor.
3 Validate IBAN check digits (2 Points)
Write a subroutine validate_checksum (file src/validateChecksum.asm), which validates the check digits
of a German IBAN. Your subroutine receives the following argument:
1. The start address of a 22 character long buffer with a German IBAN.
The subroutine returns the result of the following calculation in the return register. The following steps show how
the result is calculated.
1. Move the first four characters to the end of the IBAN.
2. Replace all letters with numbers, where A = 10, B = 11, …, Z = 35.
3. Calculate the remainder of the division by 97. This is the return value.
An example:
IBAN: DE68 210501700012345678
Reordering: 210501700012345678 DE 68
Digit substitution: 210501700012345678 1314 68
Remainder: 210501700012345678 1314 68 mod 97 = 1
You can use the subroutine modulo_str from the previous task to calculate the remainder.
The check digits are valid if the remainder is 1.
4 Generate IBAN (2 Points)
Write a subroutine knr2iban (file src/knr2iban.asm), which calculates a German IBAN with valid check digits
from a KNR and a BLZ. Your subroutine receives the following arguments:
1. The target buffer for the IBAN with space for 22 characters.
2. The BLZ as an 8 character long buffer.
3. The KNR as a 10 character long buffer.
To calculate the check digits, the function from the previous task can be used. For this, the 2nd and 3rd character
of the IBAN are set to 0. The check digits are then the difference of 98 and the result of the validation function.
A single digit check digit is prefixed with a 0.
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5 Validate IBAN check digits without intermediate memory (2 bonus points)
Write a variant of validate_checksum (file src/bonus/validateChecksum.asm), which validates the IBAN
check digits without writing intermediate results to memory. The subroutine must return the same result as
validate_checksum from task 3. In particular, any syscall or memory write disqualifies the solution.
Do not change the data segment, define macros, or define multiple text segments in the file src/bonus/validateChecksum.asm.
To qualify for the bonus points, all other tests must pass as well.
6 Evaluation
For every task there are public, daily as well as eval tests. The public tests are available in your local repository
and can be executed at any time. The next section will detail how to run those tests. You have to pass all public
tests for a task to get any points for that task. Note that a task can contain multiple subtasks, as seen with task ??.
Every public test of every subtask must be passed.
The daily tests are not available locally. These are scheduled to run after you upload your project to our server
(git push). After running the tests you will be notified via e-mail and can lookup the results in the CMS. Based
on the limited server capacity, it might take a while before the tests are run. We only guarantee that you get the
tests results once per day.
Finally, the eval tests will be used to rate the projects upon completion. These tests are unavailable to you.
7 Executing Tests and Debugging
Execute the command ./run_tests.py in the root directory of the project to test your implementation. By default
all public tests in the directory tests/pub are run. To run only specific tests, use the option -t test_name_1
...test_name_n to run only the tests with names test_name_1 through test_name_n. For example, execute
./run_tests.py -t test_check_win1 to run the public test test_check_win1 only. To list all test names,
use the -l option: ./run_tests.py -l.
The output of the tests is colored to make the results more clear. This should display correctly in the majority of
terminals, including the integrated terminal of Visual Studio Code. If the colored output poses a problem for the
terminal you use, you can disable it with the option -nc.
If a test fails, you can debug it in MARS. The command ./build_testbox tests/pub/test_X.asm copies the
test as well as your implementation into the folder testbox/. From there you can start the test using MARS. Note,
that only the files given in the task descriptions are included in the evaluation and the automated tests. Therefore
do not commit additional files, especially not in the testbox/ folder.
Self-written Tests
We recommend writing your own tests to supplement the given public tests. You can put your own test files into
the folder tests/student.
A test comprises two files, test_name.asm contains the test file while test_name.ref contains the expected
console output of the test. The printed output of the test is checked against the content of the reference file,
including newlines and spaces. If the content matches, the test is passed. Please use the public tests as a reference.
With the option -d dir_1 ... dir_n, you can run all tests contained in the subdirectories dir_1 through
dir_n of tests/. For example, with ./run_tests.py -d pub student, you can run all public tests and all of
your own tests in sequence. The option can be combined with the -t option. Use ./run_test.py -d student
-t test_X to selectively run the self-written test test_X.
Remember that when consecutively printing two integers with a syscall, no space is produced between them
automatically, which for example leads to the ambiguous output “11” if the value “1” is printed twice. Make sure
you format the printed output appropriately when writing your tests.
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Scripts for the bonus task
Analog to the regular test programs, there is the script build_bonusbox with which you can debug your solution
to the bonus task. The script build_bonusbox also copies the project with the implementation of the bonus task
to the folder bonusbox/, where you can start it with MARS. You can invoke run_tests.py with the argument
-b to run the tests with your bonus task implementation.
Submission of Solutions
git push until 09. May 2023, 23:59.
Hints
1. The file src/util.asm contains useful subroutines that you can use for this project. Some of the subroutines
implemented there should be familiar to you from the MIPS exercise sheet. You should not change this file
as we will use the original version for the automatic tests.
2. Remember that your subroutines also have to implement the calling convention.
3. For your submission, only the files in the folder src/ whose names are given in the task description will be
considered.
4. Please note that only the version of MARS installed on the virtual machine is supported by us. This differs
from the official versions in some details.
5. We point out that no guarantees can be given for the generated IBANs, BLZs and KNRs.
6. The description of the procedure for calculating the check digits is largely based on the proposed method
(http://de.wikipedia.org/wiki/IBAN#Validierung_der_Pr.C3.BCfsumme) for verifying the check
digits described on Wikipedia.
7. Document your program with code comments. This makes the code more readable and helps you to debug
your program in MARS.
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Problem Debugging
Work on Project
Encounter a Problem
All public tests pass? Look at failing tests
Write more tests
Still a problem?
Look at forum.
Found the problem?
Discuss in the forum Can be asked in the forum?
Visit office hour
Fix the code