I have a MIPs project that involves inputting a String value and having it decrypted or encrypting it by subtracting / adding an integer value in each character's ascii value(an input), then flipping a bit (bitshifting, another input value) and print it back out. I believe I've written the prompt to read and iterate through the string input, but I don't know how to implement or write the subroutines for adding, shifting each character. Any help is appreciative

.data

prompt: .asciiz "enter 'e' or 'd' to encrypt or decrypt:"

inspace: .space 100

plaintext: .asciiz "Enter text to Encrypt: "

encryptedText: .asciiz "Encrypted Text:"

lameText: .asciiz "Enter text to Decrypt:"

decryptedText: .asciiz "Decrypted Text:"

data: .space 100

addKey: .asciiz "Enter addition key:"

toggleKey: .asciiz "Enter bit toggle key:"

wrongInput: .asciiz "Enter a valid input instead"

bitKey: .asciiz "Enter toggle key"

.text

main:

start:

#encrypt or decrypt

la $a0,prompt

li $v0,4

syscall

#read input

la $a0,inspace

la $a1,5

li $v0,8

syscall

lb $t2,0($a0)

# encrypt

beq $t2,101,Plaintext #if $t2 = ascii value e,go to plaintext

# decrypt

beq $t2,100,decryptText #if t2 = ascii value d, go to decryptText

# incorrect input

la $a0,wrongInput

li $v0,4

syscall

# terminates program if a wrong input entered

li $v0,10

syscall

Plaintext:

# Read Plain text value

la $a0,plaintext

li $v0,4

syscall

la $a0,data

la $a1,40 # Maximum 40 characters can be read ( This can be changed )

li $v0,8

syscall

la $t0,($a0) # Entered string is stored in the t0 register

li $t1,0 # string length

# Read Key

la $a0,addKey

li $v0,4

syscall

li $v0,5

syscall

move $t3,$v0

#read shift key

la $a0,bitKey

li $v0,4

syscall

li $v0,5

syscall

move $t2,$v0

Encrypt:

lb $t4, 0($t0) # The first character is read

beq $t4,10,end # Terminate program on the

beqz $t4,end # Terminate Program when the end of the string is reached

jal addShift

PrintEncryptChar:

la $a0,encryptedText

li $v0,11 # print the encrypted character

syscall

add $t0,$t0,1 # Points to the next character

add $t1,$t1,1 # length is incremented

j Encrypt

decryptText:

# Read decrypt text value

la $a0,lameText

li $v0,4

syscall

la $a0,data

la $a1,40

li $v0,8

syscall

la $t0,($a0) # Entered string is stored in the t0 register

li $t1,0 # string length

# Read Key

la $a0,addKey

li $v0,4

syscall

li $v0,5

syscall

move $t3,$v0

#read bitKey

la $a0,bitKey

li $v0,4

syscall

li $v0,5

syscall

move $t2,$v0

Decrypt:

lb $t4, 0($t0) # First character is read

beq $t4,10,end # Terminate program when is pressed

beqz $t4,end # Terminate program when the end of the string is reached

jal subShift

PrintDecryptChar:

la $a0,decryptedText

li $v0,11 # Print the Decrypted character

syscall

add $t0,$t0,1 # Points to the next character

add $t1,$t1,1 # length is incremented

j Decrypt

end:

li $v0,10

syscall

#adding/ subtracting ascii value

addShift:

jr $ra

subShift:

jr $ra