Question 1 [10 Marks]
Write a program in MIPS32 assembly language which takes three input arguments: register A will receive the initial address of a string, register B will receive a character, and register C will receive another character. Within the string A, your program will replace any occurrence of the character stored in register B by the character stored in register C. Finally, output the replaced string in register A. For example:
Input string in register A: common
Input character in register B: m
Input character in register C: t
Output string in register A: cotton
Question 2 [15 Marks]
Implement a MIPS32 program which prompts user two integer inputs x, y from the console and calculate the following expression in signed 32-bit arithmetic:
x3 +3x2y+3xy2 +9y3
Note that you are NOT allowed to use pseudo-instructions with overflow checking for the calculation (e.g. you cannot use mulo). If an overflow occurs during any step of the calcu- lation, you should print an error message instead, and stop the program.
Hint: You could simplify the expression before calculation. Please remember to test your program with a range of different inputs, for example: x = 2, y = 3; x = −3, y = 4; x = 1000, y = 150000; etc.
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Question 3 [25 Marks]
Implement a MIPS-version of the strncmp() C function, as standardized by the ISO C stan- dard.
Background
The format of strncmp() is defined below:
int strncmp(const char *s1, const char *s2, size_t n); Quoted from the ISO description:
“The strncmp() function shall compare not more than n bytes (bytes that follow a NUL character are not compared) from the array pointed to by s1 to the array pointed to by s2. The sign of a non-zero return value is determined by the sign of the difference between the values of the first pair of bytes (both interpreted as type unsigned char) that differ in the strings being compared. Upon successful completion, strncmp() shall return an integer greater than, equal to, or less than 0, if the possibly null-terminated array pointed to by s1 is greater than, equal to, or less than the possibly null-terminated array pointed to by s2 respectively.”
Your Task
Given the following C code snippet:
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#include
#include
int main() {
char s1[5] = STRING 1;
char s2[6] = STRING 2;
int n = N;
int result = strncmp(s1, s2, n);
printf(“The result is %d.”, result);
return 0;
}
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Note: To execute the code snippet above, you may need to replace the RED colored content by syntactically correct C code. For example:
6 char s1[5] = “abcd”;
7 char s2[6] = “abcde”;
8 int n = 2;
Then the program should output
The result is 0.
Your are required to implement the MIPS assembly code that returns EXACTLY the same result as effectively calling the strncmp() function in line 10 of the code snippet above. You should not change any parts in the above code snippet, except the red colored content. No marks is awarded to this question if this requirement is not followed.
Input:
Once you execute your code, at the simulator console, by invoking the appropriate syscall, your program should intake a string in the following format (Px indicates Parameter x):
P1:STRING 1;P2:STRING 2;P3:N;
where the RED colored content should be replaced in the same way as the above C snippet.
For example:
P1:”abcd”;P2:”abcde”;P3:2;
Output:
After your code is executed based on the above input, by invoking the appropriate syscall, at the simulator console, your program should output the corresponding strncmp result. For the example above, the output should be:
0
What happens if strncmp() returns an error?
At the simulator console, your program should output the following message below. Note that: you do not have to specify the error, but make sure your program generates exactly this error message whenever strncmp() generates any error message.
An error has occurred.
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Resources
1. You may need to refer to the ASCII Table. Note: No “Extended ASCII Codes” need to be considered in this question.
2. Use https://www.programiz.com/c-programming/online-compiler/ as the standard strncmp() behavior reference. You can copy and past the C code snippet in Page 4 into this online C gadget and run, to obtain the referential strncmp() results. Namely, your program should output exactly the same ‘result’ value (except errors) as the C code outputs in this online gadget.
3. Click here to refer to the formal definition of strncmp() function.
4. Feel free to post questions in Moodle Discussion Forum, or email us regarding your doubts
for clarification. Especially, with doubts in this question, contact Dr. Heng directly.
Evaluation
1. Out of the 25 marks for this question, TEN (10)
Each correct answer is rewarded 2.5 marks. Each incorrect answer is rewarded 0 mark. Your output answer should follow exactly the output requirement given in this question, otherwise it would be deemed incorrect.
2. Unless otherwise specified, we will use https://www.programiz.com/c-programming/ online-compiler/ as the standard strncmp() behavior reference, to evaluate your pro- gram output.
3. Good luck! Enjoy MIPS Programming. Remember to submit your coursework on time.
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APPENDIX 1
Rubrics Q1
Weight (100)
Zero (0%)
Poor (20%)
Pass (40%)
Good (60%)
Excellent (80%)
Outstanding (100%)
Basic Function
40
No answer or all normal test cases failed
Iterative implementation, errors in normal test cases
Iterative implementation, no error in normal test cases, errors in special test cases
Iterative implementation, no error in normal test cases, no error in special test cases, other MIPS usage errors
Iterative implementation, no error in normal test cases, no error in special test cases, no MIPS usage errors
Excellent level + special considerations in data/control hazards (Encourage self-explorations)
Prompt
20
No prompt
Basic prompt to allow user’s input
Advanced prompt to guide user’s input to ensure normal input cases
Advanced prompt to guide user’s input to ensure normal input cases and special input cases
Advanced prompt to guide user’s input and warn consequences of special input. Present informative message to let user know of special input results
Advanced prompt to guide user’s input and warn consequences of special input. Present informative message to let user know of special input results. Ensure service availability
Documentation
20
No comment. Very poor coding style
Few comments. Poor coding style
Insufficient comments. Good coding style
Comments on key instructions. Good coding style
Clear comments to explain the logic flow. Good coding style
Professional comments explaining program information, input/output, design considerations, etc. Good coding style
Input Test
20
No input test
Evidence of attempted input test, but failed
Attempted input test, only ensuring normal input
Identify one type of special input, reply with corresponding prompt
Identify and handle two types of special input, reply with corresponding prompt
Identify and handle more than two types of special input. Reply with excellent prompt for user’s next input. Exhibit intelligence
APPENDIX 2
Rubrics Q2
Weight (100)
Zero (0%)
Poor (20%)
Pass (40%)
Good (60%)
Excellent (80%)
Outstanding (100%)
Basic Function
40
No answer or all normal test cases failed
There is answer, but errors in normal test cases
Iterative implementation, no error in normal test cases, errors in abnormal test cases
There is answer, no error in normal test cases, no error in abnormal test cases, other MIPS usage errors
There is answer, no error in normal test cases, no error in abnormal test cases, no MIPS usage errors
Excellent level + special considerations in data/control hazards (Encourage self-explorations)
Prompt
20
No prompt
Basic prompt to allow user’s input
Advanced prompt to guide user’s input to ensure normal input cases
Advanced prompt to guide user’s input to ensure normal input cases and abnormal input cases
Advanced prompt to guide user’s input and warn consequences of abnormal input. Present informative message to let user know of abnormal results
Advanced prompt to guide user’s input and warn consequences of abnormal input. Present informative message to let user know of abnormal results. Ensure service availability
Documentation
20
No comment. Very poor coding style
Few comments. Poor coding style
Insufficient comments. Good coding style
Comments on key instructions. Good coding style
Clear comments to explain the logic flow. Good coding style
Professional comments explaining program information, input/output, design considerations, etc. Good coding style
Input Test
20
No input test
Evidence of attempted input test, but failed
Attempted input test, only ensuring normal input
Identify one type of abnormal input, reply with corresponding prompt
Identify and handle two types of abnormal input, reply with corresponding prompt
Identify and handle more than two types of abnormal input. Reply with excellent prompt for user’s next input. Exhibit intelligence