并发症递归的MIPS代码反转字符串

Question

我已经写了这个MIPS递归反转字符串的代码。但是，输出结果与用户输入的结果相同。有人可以帮助我，并指出我哪里错了？请尽可能尽快回复。

# Program to reverse a string input by the user 

.data 

.align 2 

array: .space 50 

input: .asciiz "Enter a string: " 

output: .asciiz "\nThe reversed string is: " 

.text 

.globl main 

main: 

     addi $s0, $zero, 50 
     addi $t0, $zero, 0 

     la $a0, input 
     li $v0, 4 
     syscall 

     la $a0, array 

     li $v0, 8 
     syscall 

initiate: 

     add $t0, $a0, $zero  # initial address 
     add $t1, $zero, $zero # count=0 
     add $t2, $zero, $zero # i=0 
     la $t0, array  # base address of the array 
     add $t3, $t0, $t2 # & array[i] 

loop: 

     lb $t3, 0($t3)  # fetch array[i] 
     beqz $t3, EndOfString # loop exits if it is a null character;array[i] !='\0' 
     bne $t3, $0, continue # otherwise loop continues 
     add $t1, $t1, 1  # count++ 

continue: 

     add $t2, $t2, 1  # i++ 
     j loop 

     addi $a1, $zero, 50 

     jal StringReversal 

EndOfString: 

     la $a0, output 
     li $v0, 4 
     syscall 

     la $a0, array 
     li $v0, 4 
     syscall 

     li $v0, 10 
     syscall 

StringReversal: 

     add $t0, $a0, $zero  # initial address 
     add $t4, $zero, $zero # j = start = 0 
     addi $t5, $a1, -1 # k = end-1 

SwapLoop: 

     add $t6, $t0, $t4 
     lb $t7, 0($t6)   # load byte array[start] 
     add $t8, $t0, $t5 
     lb $t9, 0($t8)  # load byte array[end-1] 
     sb $t7, 0($t8)  # array[end-1] = array[start] 
     sb $t9, 0($t6)  # array[start] = array[end-1] 
     addi $t4, $t4, 1  # j++ 
     addi $t5, $t5, -1 # k-- 
     slt $t9, $t5, $t4 
     beqz $t9, SwapLoop 
     jr $ra 

Answer 1

在你continue标签，它看起来好像j loop被称为太早，因此

addi $a1, $zero, 50 

jal StringReversal 

永远达不到，因此在StringReversal标签的指令不执行。

Answer 2

# Program to reverse a string input by the user 
.data 
.align 2 
    array: .space 50 
    input: .asciiz "Enter a string: " 
    output: .space 50 
    size: .word 49 
.text 
j main 

length: 
    # return length of the input string 
    # $a0 - address of string 
    # $v0 - length of the string 
    move $v0, $zero # set $v0 to 0 
length_loop: 
    lb $t0, 0($a0) 
    beqz $t0, length_end 
    addi $v0, $v0, 1 
    addi $a0, $a0, 1 
    b length_loop 
length_end: 
    subi $v0, $v0, 1 
    jr $ra 

reverse: 
    # $a0 - address of string to reverse 
    # a1 - length of the string 
    # a2 - address of string where to store the reverse 
    addi $sp, $sp, -4 
    sw $ra, 0($sp) 
    bltz $a1, reverse_end 
    lb $t0, 0($a0) 
    subi $a1, $a1, 1 
    subi $a0, $a0, 1 
    sb $t0, 0($a2) 
    addi $a2, $a2, 1 
    jal reverse 
reverse_end: 
    lw $ra, 0($sp) 
    addi $sp, $sp, 4 
    jr $ra 


main: 
    addi $s0, $zero, 50 
    addi $t0, $zero, 0 

    la $a0, input 
    li $v0, 4 
    syscall 

    # read string from the user into $a0 
    la $a0, array 
    lw $a1, size 
    li $v0, 8 
    syscall 

    # reverse the string 
    jal length # $v0 contains length of string 
    la $a0, array 
    move $a1, $v0 
    add $a0, $a0, $a1 # pointer to the last character 
    la $a2, output 
    jal reverse 

    # print the reverse string 
    la $a0, output 
    li $v0, 4 
    syscall 

输出：

Enter a string: hello 

olleh 
-- program is finished running (dropped off bottom) --