How to write a program that applies run length encoding compression to a given string using MIPS - mips

Question

Dynamic memory allocation and strings
Write a program that applies run length encoding compression to a given string. Follow the below steps:
Dynamically allocate memory from heap for two strings (an input string and an output string).
Read an input string (a-z, A-Z) of size less than 40 characters in this dynamic memory.
Iterate over the string looking for consecutive occurrences of the same character and replace
them with the character and a count.
Example, if the input string is AAAAAA, the output string should be A6. If you see
BBCCCCCCCCCCCCC, the output should be B2C13.
Note that the number 13 is represented as two separate characters ‘1’ and ‘3’ in the output string.
Single character occurrences do not need a count.
The output string should also be stored in the dynamic memory before it is displayed on the
console.
Implement a loop back to the main function. See the prompts below:
“Enter a string:”
“Compressed string is:”
“Do you want to apply run length encoding again?”
Test the program using the following data:
a. Input: AAAAaaabbcde Compressed string: A4a3b2cde
b. Input: XXXXXXXXXXYYZZZWERTT Compressed string: X10Y2Z3WERT2
.data
Prompt1: .asciiz "\n Enter a string."
.text
main:
li $v0, 4
la $a0, Prompt1
syscall
li $v0, 9
li $a0, 80
syscall
move $s0, $v0
li $v0, 8
la $a0, 0($s0)
li $a1, 40
syscall
move $t0, $a0
li $t4, 0
Loop:
lb $t1, 0($t0)
sb $t1, 40($s0)
addi $t0, $t0, 1
addi $t4, $t4, 1
addi $s0, $s0, 1
beq $t1, 0, End
j Loop
End:
neg $t4, $t4
add $s0, $s0, $t4
li $v0, 4
la $a0, 40($s0)
syscall

Answer 1

Generally, the algorithm should look something like this:
Get the pointers to your input string and your output buffer.
Loop:
Read the nth letter.
If it's the null terminator, exit.
Read the (n+1) th letter. If it's the null terminator, GOTO 5. If it's the same as the nth letter, GOTO 6.
Otherwise, add 1 to your index into the input string and GOTO 2.
Compress:
Create a counter variable for how many times you've seen the same letter in a row. It should start at two since you've seen two letters that are the same.
Add 2 to your index.
Compress_Loop:
Read the nth letter (remember, we added 2 to n in step 6.)
If it's not the same letter we've saw in Step 4, GOTO 11. Otherwise, continue.
Add 1 to your index into the input string, and add 1 to the counter variable, then GOTO 8.
Store the letter we saw in Step 4 into the output string.
Convert the counter variable to a string, and store it in the output string.
Adjust your index into the output string past what you just wrote.
GOTO 2.