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CS2110 - Homework 5 - Intro to Assembly - Solved
GCD
To start you off with this homework, we are implementing the GCD function! Store the result of the operation in the label ANSWER. Arguments A and B are stored in memory, and you will load them from there to perform this operation. Implement your assembly code in gcd.asm.
Suggested Pseudocode:
ANSWER = 0; while (a != b) { if (a > b) { a = a - b;
} else { b = b - a;
}
}
ANSWER = a;
2.2 Part 2: Array Merge
The second assembly function is to implement the “merge” part of merge-sort into an array in memory. You will be merging two pre-sorted input arrays into a third array, so that the third array is also sorted. The third array will have enough space for the final answer. Use the pseudocode to help plan out your assembly and make sure you are sorting it properly! Implement your assembly code in merge.asm.
Suggested Pseudocode:
x = 0; // first index of ARR_X y = 0; // first index of ARR_Y z = 0; // first index of ARR_RES while (x < LENGTH_X && y < LENGTH_Y) { if (ARR_X[x] <= ARR_Y[y]) { ARR_RES[z] = ARR_X[x]; z++: x++;
} else {
ARR_RES[z] = ARR_Y[y]; z++; y++;
}
}
while (x < LENGTH_X) { ARR_RES[z] = ARR_X[x]; z++; x++;
}
while (y < LENGTH_Y) { ARR_RES[z] = ARR_Y[y]; z++; y++;
}
// the final merged array should be in ARR_RES
2.3 Part 3: Studly Caps
The third assembly function is to turn a null-terminated string into a string with studly caps. Studly caps, also known as alternating caps, sticky caps, or occasionally “SpongeBob case”, consists of alternating the letters in a string between lowercase and uppercase. In this function, the first letter is expected to be lowercase and the subsequent letters alternate between uppercase and lowercase depending on the index. The index starts at 0, if the index is even, the character should be lowercase. If the index is odd, the character is expected to be uppercase.
The label STRING will contain the address of the first character of the string to be converted. Convert the string in-place, so that the result string is also stored at the same label STRING. Remember that strings are just arrays of consecutive characters. You are given four constants to use in your program, LOWERA which is the value of the ASCII character ‘a’, LOWERZ which is the value of ‘z’, UPPERA which is the value of ‘A’, and UPPERZ which is the value of ‘Z’. Implement your assembly code in studlyCaps.asm
Assume that the strings are random: they can contain characters, numbers, spaces and symbols.
To convert a character between lowercase and uppercase, refer to the ASCII table and remember that each of these characters are represented by a word (16-bits) in the LC-3’s memory. This is a null-terminated string, meaning that a 0 will be stored immediately after the final character in memory!
NOTE:
• 0 is the same as ‘\0’
• 0 is different from ‘0’
Suggested Pseudocode:
string = "TWENTY 1 ten" i = 0;
while (string[i] != 0) { if (i % 2 == 0) {
// should be lowercase if (’A’ <= string[i] <= ’Z’) { string[i] = string[i] | 32;
}
} else {
// should be uppercase if (’a’ <= string[i] <= ’z’) { string[i] = string[i] & ~32;
} } i++;
}
The result here is tWeNtY 1 TeN.
2.4 Part 4: Palindromes
For the final problem, your goal is to determine whether a null-terminated string is a palindrome. A palindrome is a word, phrase or a sequence of numbers that reads the same backward as forward. For instance, “racecar” is a palindrome because it is “racecar” when read both backward and forward.
The label STRING will contain the address of the first character of the string to be checked. Remember that this string is null-terminated. The result will be stored at the label RESULT. If the given string is a palindrome, the result should be set to 1. Else, it should be set to 0. Implement your assembly code in palindrome.asm
Assume every alphabetic character in the string is in lowercase. The string can contain numbers.
NOTE:
• 0 is the same as ‘\0’
• 0 is different from ‘0’
Suggested Pseudocode:
string = "racecar"; len = 0;
// to find the length of the string while (string[len] != ’\0’) { len = len + 1;
}
// to check whether the string is a palindrome result = 1; i = 0; while (i < length) { if (string[i] != string[length - i - 1]) { result = 0; break;
}
i = i + 1;
}
• Mac/Linux Users:
(a) Navigate to the directory your homework is in (in your terminal on your host machine, not in the Docker container via your browser)
(b) Run the command sudo chmod +x grade.sh
(c) Now run ./grade.sh
• Windows Users:
(a) In Git Bash (or Docker Quickstart Terminal for legacy Docker installations), navigate to the directory your homework is in
(b) Run chmod +x grade.sh
(c) Run ./grade.sh
When you run the script, you should see an output like this:
Copy the string, starting with the leading ’B’ and ending with the final backslash. Do not include the quotation marks.
Side Note: If you do not have Docker installed, you can still use the tester strings to debug your assembly code. In your Gradescope error output, you will see a tester string. When copying, make sure you copy from the first letter to the final backslash and again, don’t copy the quotations.
2. Secondly, navigate to the clipboard in your Docker image and paste in the string.
3. Next, go to the Test Tab and click Setup Replay String
4. Now, paste your tester string in the box!
5. Now, Complx is set up with the test that you failed! The nicest part of Complx is the ability to step through each instruction and see how they change register values. To do so, click the step button. To change the number representation of the registers, double click inside the register box.
6. If you are interested in looking how your code changes different portions of memory, click the view tab and indicate ’New View’
7. Now in your new view, go to the area of memory where your data is stored by CTRL+G and insert the address
8. One final tip: to automatically shrink your view down to only those parts of memory that you care about (instructions and data), you can use View Tab → Hide Addresses → Show Only Code/Data.
