FIT1047 Computer Systems and Security: Develop a MARIE Application

Marie Task

In this task, you will develop a MARIE application that performs some manipulation of strings. We will break it down into small steps for you.

Most of the tasks require you to write the code, test your code with sample inputs and write the analysis of the outcome explaining the expected outcome. Your MARIE program must contain brief comments explaining the purpose of your subroutines and main programs (to be written in the .mas file). You must submit your code as .mas files together with the rest of your assignment.

The description of your experiences while testing your code with test inputs and the subsequent analysis needs to be submitted as part of the main PDF file you submit for this assignment. In some cases wherever it is appropriate, you may add test data to your program to prepare test cases. These test cases, which are mostly appropriate for programs processing numeric data, should be working without requiring much input from the user, i.e. a self-contained MARIE assembly program.

The following section introduces some concepts that you need for the rest of the assignment.

Name as Strings

A string is a sequence of characters. It is the basic data structure for storing text in a computer. There are several different ways of representing a string in memory and how to deal with strings of arbitrary length. For this assignment, we will use the following string representation:

• A string is represented in a contiguous memory location, with each address containing a single character.

• The characters are encoded using the ASCII encoding. End of a string is marked by the ASCII character comma

• A name will be composed of two strings, namely, FirstName and Last

• End of a name will be marked by another ASCII character dot

Representation of Strings in Memory using ASCII code

An illustrated example below showing how a name “John Noah” would be represented in memory (written as hexadecimal numbers):

Note that for a string with n characters, we need n + 2 words of memory in order to store all the characters belonging to a first name, a last name, the additional ‘,’ and ‘.’.

Strings in MARIE

In MARIE assembly language programming, we can make use of the ADR command, the HEX

keyword and a label “myName” to put a string into memory location:

After assembling the above MARIE code, we will find that the variable (or label) myNameAdd contains the address of the string i.e. the address of the first character ‘J’ of the string “John Noah”. An example below shows how to access the first character of the above string and display:

start,  LoadI  Output ……… myNameAdd
              Halt

2.1 Write a MARIE Program to Store Multiple User Entered Names in Consecutive Memory Rows and Print Them at the End of Data Entry. (15 marks)

Prepare a MARIE program to enter full names using Unicode / ASCII characters. Limit each part of a name (First Name or Last Name) to at most 5 characters – if a name is longer, you can shorten it (limit the maximum number of characters per full name to 12). After assembling and running your MARIE program, it should prompt for entering names using a keyboard. For the MARIE simulator, Unicode input from the keyboard can only be entered character by character. Your program should store the names in MARIE memory and print them at the end.

(i). Subroutine subInputNames: The first part of your program should focus on getting the full names as input from the keyboard and storing them in a particular location in MARIE memory. For this task, prepare a MARIE subroutine called subInputNames. Your subroutine should input (Unicode /ASCII) ‘,’ terminated First name and (Unicode /ASCII) ‘.’ terminated Last name as described in the previous section. The names have to be stored starting from the memory address 300H. A single name (First Name and Last Name) is to be stored in one row of MARIE memory. After entering a full name, a Unicode/ASCII ‘.’ will be stored to mark the end of the name in the memory, and the program should proceed to take the next name, which is to be stored at memory location 310H. This location is one row (16 words) ahead from the memory location of the previous name entry. You can use memory locations 320H, 330H, … to store more names respectively. After entering a full name, a ‘$’ from input will terminate the entire name entry process and will return control to the calling program. You have to store the ‘$’ in the memory to mark the end of the name database. Your program must be capable of accepting names one after the other, until a user enters a ‘$’ to stop taking inputs. You can verify the correct working of your program by viewing the memory content starting from #300H.

(ii). Subroutine subPrintString: In the second part of your program, prepare a MARIE subroutine called subPrintString that can print all the full names stored. This subPrintString subroutine should access all the full names in the memory (that are entered and saved by the subInputNames earlier) and printout using the “Output” instruction.

Start by using a label “PrintNameAdd” that holds the start address of a name string (like, myNameAdd in the example above). The code should then load a character from that address, output it if it is not ‘,’, then increment the address by one, and keep doing that until the character loaded from the address is a ‘,’ (which signals the end of the first name). Then, instead of printing (or output) the ASCII “,” character, print an ASCII “Space” character, and proceed to print the second part of the name string, i.e. Last Name until the character loaded from the address is a ‘.’ (which signals the end of the Last Name). Then, when you load the ASCII ‘.’ which marks the “end of a name”, instead of printing (or output) the ASCII “.” character, print an ASCII “New Line” character. Then your program should proceed to print the next name. If the loaded character is ‘$’, the subroutine needs to stop printing and gives control to the main program. While testing your code and writing the test cases for this task, you have to use at least three names (your First Name and Last Name, your friend’s name and your tutor’s name). Please note that these names should not be hard coded and assigned labels to identify each of these three names.

To receive full marks, your code needs to be in the form of a main program and use of subroutine that can be called using the JnS instruction. Save your code as “2_1_Enter_and_PrintingNames.mas”.

2.2 A MARIE Subroutine to Change Cases of Characters of User Entered Names (Upper to Lower or Lower to Upper Cases) and Print (15 marks)

Write a subroutine to change cases of all the characters of a user entered name string: Upper to Lower case or Lower to Upper case. Name the subroutine as subChangeCase. This subroutine modifies all the characters of a string in memory (from lower to upper or upper to lower cases). The program should then print the original and the modified string. Submit your MARIE code and documentation of test cases converting at least three names. To receive full marks, the main program from section 2.1 must be extended to print the original name string and the modified changed-case name string by calling the respective subroutines. Name your MARIE code file as “2_2_ChangeCase.mas”.

Hint: you can easily identify the uppercase or lowercase ASCII value ranges through the ASCII table and notice the numeric difference between the uppercase and lowercase characters.

2.3 A MARIE Subroutine to Substitute Characters of User Entered Names and Print (20 marks)

In this section, we are going to implement substitution of characters of a user-entered name. It replaces each character in a string by a different character of the alphabet defined by a reverse character shift. A shift of all alphabets in reverse order as. shown in the table below.

Please note the use of lower case alphabets only, and we will substitute only “alphabets”.

To substitute, the corresponding letter in the bottom row replaces each letter in the top row. You will implement mapping in MARIE by a lookup table, storing the result of substitution for each letter. The lookup table below maps the shifted keys.

A subroutine to perform substitution on a string

In this task, you will implement a MARIE subroutine called subSubstitution that can perform substitution on a string. You need to display the string before and after the substitution process. You can assume that the string only contains lower case characters. For each letter in the string, you will need to load the correct value for its substitution from the table “mySubstKey1”, and then store that value in another memory location for printing the substituted output.

During the substitution process, the following transformation (in the memory) will occur based on the lookup table given above as the key for substitution.

Moreover, the new substituted string can be stored in the new memory location. Please note that, during the substitution process, ASCII value for “,” and ‘.’ remains unchanged. To receive full marks, your code needs to be in the form of a subroutine that can be called using the JnS instruction. You need to write a MARIE main program to call this subroutine.

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