CODEWITHSUNDEEP
assemblymips
user1814946
user1814946

Reputation: 181

QTSpim MIPS program help. Program errors in conversion from ascii string to integer

I am working on a mips program to convert numbers from ascii string into integers, with the parameter that it should accept positive and negative integer decimal strings. I know this is a pretty common a assignment but I wasn't able to resolve my problems online. I was able to get some tips, but still receiving errors when trying to run the program.

Here is the code I have at this time: 

main:    # convert string to integer
li $t6, 0x00    # $t6 = 0
li $t7, 0x09    # $t7 = 9
li $v0, 0x00    # initialize $v0 = 0
move $t0, $a0   # $t0 = pointer to string
lb $t1, ($t0)   # load $t1 = digit character

loop:
blt $t1, $t6, Done  # char < 0
bgt $t1, $t7, Done  # char > 9
subu $t1, $t1, $t6   # convert char to int
mul $v0, $v0, 10    # multiply by 10
add $v0, $v0, $t1   # $v0 = $v0 * 10 + digit
addiu $t0, $t0, 1   # point to next char
lb $t1, ($t0)        # load $t1 = next digit
bne $t1, $0, loop   # repeat if not end of string
jr $ra   # return integer

Done:          #exit program if string not a number
li $v0, -1      # return -1 in $v0
jr $ra

I am getting tons of errors trying to run this and I just have no idea why. This is my first time writing in mips so I don't have a feel for it. Any tips? Thanks!

I did fix the errors I could understand. There is no TA and no available tutors in my area. I'd really like help understanding this if possible. I'd love some constructive replies.

Upvotes: 0

Views: 3441

Answers (1)

gusbro
gusbro

Reputation: 22585

The code you provided tries to convert unsigned (positive) integers from an asciiz buffer to an integer. It fails because you provided the wrong constants for digits '0 and '9'. '0' in the ASCII table uses code 0x30, and '9' uses code 0x39, or alternatively just use '0' and '9' to load those immediates.

Therefore, to fix your program you should use:

li $t6, '0'    # $t6 = 0x30
li $t7, '9'    # $t7 = 0x39

To allow the routine to correctly parse negative integers you would need to:

  • Read the first input character to see whether it is a minus sign '-', maybe setting the result from this comparison in some unused register. If it is a negative number, move pointer to the next char
  • Now continue parsing the string as you did, except that you have to take into account if the number was negative. If the number was negative instead of issuing $v0 = $v0 * 10 + digit you should issue $v0 = $v0 * 10 - digit

Upvotes: 1

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