string - 带递归的 MIPS 程序

Question

这是我这个学期的最后一个作业。我需要将一个以 33 为底的数字转换为以 10 为底的数字（这部分有效），并且需要通过递归来完成（这部分无效）。我编写了这段代码，但出现了一个错误，称为“异常 5”。

为什么会这样，我该如何解决？我真的不知道如何解决它。

这是我的代码：

    .data
  userInput:    .space  700
  empty:   .asciiz "Input is empty."
   long:    .asciiz "Input is too long."
  invalid: .asciiz "Invalid base-33 number."

.text

ErrorLong:
#prints message for input that is too long
  la $a0, long
  li $v0, 4
  syscall
  j end

ErrorInvalid:
#prints message for invalid input
  la $a0, invalid
  li $v0, 4
  syscall
  j end

ErrorEmpty:
#prints message for empty string
  la $a0, empty
  li $v0, 4
  syscall
  j end

.globl main

main:
  li $v0, 8
  la $a0, userInput
  li $a1, 200
  syscall

Rid:
#takes care of leading spaces
li $t9, 32 # space
lb $t8, 0($a0)
beq $t9, $t8, Character
move $t8, $a0
j length

Character:
addi $a0, $a0, 1
j Rid

#takes care of length
length:
addi $t0, $t0, 0
addi $t1, $t1, 10
add $t2, $t2, $a0

#itertates through the array
traverse:
lb $s2, 0($a0)
beqz $s2, discovered
beq $s2, $t1, discovered
addi $a0, $a0, 1
addi $t0, $t0, 1
j traverse

#busted empty space or input that violates limit
discovered:
#if it's empty go to case for empty which outputs 
beqz $t0, ErrorEmpty
slti $t4, $t0, 5
#if it's too long, go to case for too long and print 
beqz $t4, ErrorLong
move $a0, $t2
#go to next verification process
j verify

#checks inputs
verify:
lb $s3, 0($a0)  #loads address here
beqz $s3, initial
beq $s3, $t1, initial
slti $t3, $s3, 48                 #invalid for anything below 0
bne $t3, $zero, ErrorInvalid
slti $t3, $s3, 58                 #legal input for everything less than or equal to 9
bne $t3, $zero, Move
slti $t3, $s3, 65                 #legal input for everything less than or equal to 65,  'a'
bne $t3, $zero, Move
slti $t3, $s3, 88                 #legal input for anything less than or equal to 88
bne $t3, $zero, Move
slti $t3, $s3, 97                 # invalid input, not numerical nor alphabetical
bne $t3, $zero, ErrorInvalid
slti $t3, $s3, 120                #legal input for lower case characters
bne $t3, $zero, Move
bgt $s3, 119, ErrorInvalid   # illegal input, out of range

#now I iterate again, this time to check for invalid input
Move:
addi $a0, $a0, 1 #iterates
j verify #goes to verification point

#first step of conversion, does the prerequisite work for translation 
initial:
move $a0, $t2  #moves content
addi $t5, $t5, 0  #$t5 has 0 now
add $s0, $s0, $t0  
addi $s0, $s0, -1 #decrement    
#load immediate puts values in registers to be used

Must:
addi $sp, $sp, -16
sw $ra, 0($sp)
sw $ra, 4($sp)
sw $ra, 8($sp)
sw $ra, 12($sp)
jal Must

ExitMust:

lw  $ra,16($sp)
lw $s4, 3($sp) 
lw $s5, 2($sp)
lw  $s6, 1($sp)
lw $s1, 0($sp)

jr $ra   #return

#li $s4, 3  #each digit
#li $s5, 2
#li $s6, 1
#li $s1, 0

translate:
lb $s7, 0($a0)   #loads digits
beqz $s7, final  #final conversion step
beq $s7, $t1, final #if branch statement is true, move to final conversion statement
slti $t3, $s7, 58  #checks for less than or equal to 58
bne $t3, $zero, Base  #OK to move forward if $t3 is not null
slti $t3, $s7, 88  #max for upper
bne $t3, $zero, Mari  #OK to go to conversion of upper characters if $t3 is not null
slti $t3, $s7, 120     #max for lower
bne $t3, $zero, Mici #OK to go to conversion of lower characters if $t3 is not null

Base:
addi $s7, $s7, -48  #conversion for regular numbers
j row

Mari:
addi $s7, $s7, -55  #conversion for upper case
j row

Mici:
addi $s7, $s7, -87  #conversion for lower case

row:  #determines which digit needs to be converted
beq $s0, $s4, one  
beq $s0, $s5, two
beq $s0, $s6, three
beq $s0, $s1, last

#first character
one:
li $t6, 35937   #values to multiply by for the power of 3
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
addi $s0, $s0, -1
addi $a0, $a0, 1
j translate

#second character
two:
li $t6, 1089   #values to multiply by for the power of 2
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
addi $s0, $s0, -1
addi $a0, $a0, 1
j translate

#third character
three:
li $t6, 33   #values to multiply by for the power of 1
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
addi $s0, $s0, -1
addi $a0, $a0, 1
j translate

#fourth character
last:
li $t6, 1    #values to multiply by for the power of 0
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
#no more need to go back to translation step


final:                  #final step
li $v0, 1
move $a0, $t5  #moves content to $a0 so it can be printed
syscall

#last system call of the program will end program
end:   #prints result
 li $v0, 10

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