I have written the following code for a programming assignment. I would appreciate some help to improve this code and see if it meets all the requirements and criteria. I would like to improve my loop and supporting continue function.
###############################
#String to int.
###############################
#########################################################################
##| The program obeys MIPS function calling convetions.
##|
##| The program accepts two arguments for function stringToInt.
##| Argument A (testInput): address of null terminated string.
##| Argument B (base): An integer in the range of 2 and 16.
##|
##| The program outputs an integer result converting the given
##| argument a into an integer.
##| If the second argument is not in the range of 2-16 the program
##| returns error message and returns the value of zero. The same
##| applies if the legal digits are not entered.
##|
##| Legality of the input
##| If the string has only the characters from '0' to '9'
##| and from 'a' to 'f' and from 'A' to 'F'
##| Input starting with '-' is accetped '+' is illegal.
##| If the digits are not legal:
##| The program prints out error message and returns value 0.
##|
##|
##|_______________________________________________________________________#
#******************************Begin***************************************
.data
############### Test Case ###################
stringInput: .asciiz "-1234" #String
base: .byte 16 #Base (2-16)
##############################################
#Prints out error message.
errorMessage: .asciiz "\nError. Please check input string."
.text
###########################################################################
# Function: stringToInt
# Excepts two arguments string address and base. Loads base argument
# into $a1 and char address into $t0. Converts string into ascii notation.
# Checks the validity of base (between 2 and 16 incluseive) and if
# the input is negative. If negative convert it using twos complement.
# If the base is not between 2-16 prints an error message return zero.
# Converts the string into integer. Terminates program at '\n' or '\0'.
stringToInt:
la $t0, stringInput #current char address in t0
li $t2, 0 #decimal equivalent intialized to 0
li $t4, 1 #power
lb $a1, base #load base into register a1
bgt $a1, 16, invalid #checks if base is valid
lb $s6, base #loads base into register s6
addi $s6, $s6, 48 # converts s6 to ascii notation
lb $s0, ($t0)
la $t5, stringInput
beq $s0, '-', negSet #checks first element of string to see if it is a minus sign
j check #jump to check
#_________________________________________________________________________#
###########################################################################
# Checks if the nubmer is negative.
negSet:
addi $s7, $zero, 1 #s1 will store a value to check if no is negative
addi $t0, $t0, 1
addi $t5, $t5, 1
#_________________________________________________________________________#
###########################################################################
#Go till end of end of input
check:
lb $t1, ($t0)
beq $t1, '\n', endCheck
beq $t1, '\0', endCheck
add $t0, $t0, 1
b check
endCheck:
#_________________________________________________________________________#
###########################################################################
# Go from last char to first, decrementing address. Compare from highest
# ascii value. If less than start address jummp to countinue4. Else invalid
loop:
sub $t0, $t0, 1
blt $t0, $t5 , valid #if less than start address stop
lb $t1, ($t0)
bgt $s6, 57, continue3 #compare from highest ascii value
bge $t1, $s6, invalid #branch to invaldi if $t1 >= $s6
j continue4 #jump to continue 4
# exit point if base is greater than 10
continue3:
# makes sure only needed values are used
continue4:
bge $t1, 'g', invalid
bge $t1, 'a', lower
bge $t1, 'G', invalid
bge $t1, 'A', upper
bge $t1, '9', invalid
bge $t1 , '0', digit
#print error message and exit.
invalid:
li $v0,1
li $a0,0
syscall
li $v0, 4
la $a0, errorMessage
syscall
b exit
#Peforms validity checks.
#Check if the vlaue is negative. (Using twos complement)
valid:
addi $t1, $zero, 1
sll $t1, $t1, 31
and $s1, $t2, $t1
bne $s1, $zero, bignegative
bne $s7, $zero, twosComplement # checkes the s7 register to see if our value is negative
# Return point after converting to negative number if a minus sign
# was detected. Print and exit.
continue2:
li $v0, 1 # Print content of t2
move $a0, $t2
syscall
b exit
# manipulates the digit to convert and checks validity.
digit:
bgt $t1, '9', invalid
sub $t3, $t1, '0' #get numeric digit value
mul $t3, $t3, $t4 #mulitply by the current power
add $t2, $t2, $t3
mul $t4, $t4, $a1 #next power
j loop #jump back to loop
#get numeric digit value
lower:
bgt $t1, 'f', invalid
sub $t3, $t1, 'a'
add $t3, $t3, 10
mul $t3, $t3, $t4 #mulitply by the current power
add $t2, $t2, $t3
mul $t4, $t4, $a1 #next power
b loop #branch to loop
#get numeric digit value
upper:
bgt $t1, 'F', invalid
sub $t3, $t1, 'A'
add $t3, $t3, 10
mul $t3, $t3, $t4 #mulitply by the current power
add $t2, $t2, $t3 #add to decimal
mul $t4, $t4, $a1 #next power
b loop #branch to loop
bignegative:
li $t7, 10 # load value 10 into register t7
divu $t2, $t7
mflo $t1 # move value of LO register into $t1
mfhi $t7 # move value of HI register into $t7
#Print t1
add $a0, $t1, $zero
li $v0, 1
syscall
# printt7
add $a0, $t7, $zero
li $v0, 1
syscall
#Ends the program and exit.
#tell the system this is the end of stringToInt
exit:
li $v0, 10
syscall
#Perform the twos complement by subracting zero. To convert
#negative input.
twosComplement:
sub $t2, $zero, $t2 # convert number to negative
j continue2 #jump to continue2
#_________________________________________________________________________#
