MIPS: removing non alpha-numeric characters from a string
- by Kron
I'm in the process of writing a program in MIPS that will determine whether or not a user entered string is a palindrome. It has three subroutines which are under construction.
Here is the main block of code, subroutines to follow with relevant info:
.data
Buffer: .asciiz " " # 80 bytes in Buffer
intro: .asciiz "Hello, please enter a string of up to 80 characters. I will then tell you if that string was a palindrome!"
.text
main:
li $v0, 4 # print_string call number
la $a0, intro # pointer to string in memory
syscall
li $v0, 8 #syscall code for reading string
la $a0, Buffer #save read string into buffer
li $a1, 80 #string is 80 bytes long
syscall
li $s0, 0 #i = 0
li $t0, 80 #max for i to reach
la $a0, Buffer
jal stripNonAlpha
li $v0, 4 # print_string call number
la $a0, Buffer # pointer to string in memory
syscall
li $s0, 0
jal findEnd
jal toUpperCase
li $v0, 4 # print_string call number
la $a0, Buffer # pointer to string in memory
syscall
Firstly, it's supposed to remove all non alpha-numeric characters from the string before hand, but when it encounters a character designated for removal, all characters after that are removed.
stripNonAlpha:
beq $s0, $t0, stripEnd #if i = 80 end
add $t4, $s0, $a0 #address of Buffer[i] in $t4
lb $s1, 0($t4) #load value of Buffer[i]
addi $s0, $s0, 1 #i = i + 1
slti $t1, $s1, 48 #if ascii code is less than 48
bne $t1, $zero, strip #remove ascii character
slti $t1, $s1, 58 #if ascii code is greater than 57
#and
slti $t2, $s1, 65 #if ascii code is less than 65
slt $t3, $t1, $t2
bne $t3, $zero, strip #remove ascii character
slti $t1, $s1, 91 #if ascii code is greater than 90
#and
slti $t2, $s1, 97 #if ascii code is less than 97
slt $t3, $t1, $t2
bne $t3, $zero, strip #remove ascii character
slti $t1, $s1, 123 #if ascii character is greater than 122
beq $t1, $zero, strip #remove ascii character
j stripNonAlpha #go to stripNonAlpha
strip:
#add $t5, $s0, $a0 #address of Buffer[i] in $t5
sb $0, 0($t4) #Buffer[i] = 0
#addi $s0, $s0, 1 #i = i + 1
j stripNonAlpha #go to stripNonAlpha
stripEnd:
la $a0, Buffer #save modified string into buffer
jr $ra #return
Secondly, it is supposed to convert all lowercase characters to uppercase.
toUpperCase:
beq $s0, $s2, upperEnd
add $t4, $s0, $a0
lb $s1, 0($t4)
addi $s1, $s1, 1
slti $t1, $s1, 97
#beq $t1, $zero, upper
slti $t2, $s1, 123
slt $t3, $t1, $t2
bne $t1, $zero, upper
j toUpperCase
upper:
add $t5, $s0, $a0
addi $t6, $t6, -32
sb $t6, 0($t5)
j toUpperCase
upperEnd:
la $a0, Buffer
jr $ra
The final subroutine, which checks if the string is a palindrome isn't anywhere near complete at the moment. I'm having trouble finding the end of the string because I'm not sure what PC-SPIM uses as the carriage return character.
Any help is appreciated, I have the feeling most of my problems result from something silly and stupid so feel free to point out anything, no matter how small.
