Need help solving question
String manipulation, loops, branches, and subroutine calls in MIPS
Background:
.asciiz stores a string with the null terminator
.ascii stores a string without a null terminator
Since MIPS stores a string as ASCII bytes, it will make sense to use the lbu/sb load/store byte instructions.
Write a MIPS program to copy a lowercase string to another string, converted to uppercase. For example: "hola" should become "HOLA". Store string lower as .asciiz and reserve space for string upper using .space.
Look up an ASCII table in hex online or in the notes and notice the difference in hex between upper and lower case letters to figure out how to easily convert from one to the other. Your program should loop until it encounters the null terminator.
Take a screen shot of the program code. Take another screen shot of the memory area after the program ran, but check the ASCII box below the memory window.
Table 1: Rubric for Problem 1
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Task
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Points
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Code screen shot
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10
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Memory screen shot
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5
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Loop ends at '\0'
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5
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Code comments, formatting
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5
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Total
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25
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Rewrite your program in #1 to use a procedure for the conversion. In other words, if you send "apple" to the procedure it will return "APPLE". Leave the rest of the code in main.
Test it on the source strings: "loop2:" and "Elephant!" In other words, code in your main program calls the procedure twice, once for each source string. You should print a memory screen shot after the program runs, showing that both strings were converted - check the ASCII box.
You should add code to check if each byte is in fact a lowercase letter, and only convert if it is; otherwise it should just copy it.
In the program for problem 1 you could use $tn registers but in this program you should follow the conventions for using $sn and $tn registers.
Also, use the directive .space for the upper case strings, reserving at least 10 bytes for each of the 2 upper strings.
Table 2: Rubric for problem 2
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Task
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Points
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Code and screen shot
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5
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Memory screen shots for 2 inputs
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10
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Correct procedure usage
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5
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Code checks a-z range
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5
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Correct use of $tn and $sn
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5
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Main code calls procedure twice
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5
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Code comments, formatting
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5
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Total
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40
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Single-step through your program through the first subroutine call and back, then answer the following questions. Copy a-g below and paste your answers/screen shot here.
What is the value of PC before you execute the jal?
What is the value of $ra before you execute the jal?
Set a breakpoint to the jr instruction and run until then. What is the value of PC before the jr?
Single step back to the main program. What address is in the next instruction?
What value is in the PC?
Write a 2-3 sentence summary describing how the PC and $ra registers change when a subroutine is called and when we return from a subroutine.