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我正在编写一个简单的 MIPS 汇编代码，它遍历字符串的字符

并找到给定子字符串的实例..

一、c代码：

for (i=0; i<length(text)-length(sub_string); i++) {

    match = TRUE

    for (j=0; j<length(sub_string); j++)
        if (text[i+j] != sub_string[j]) {
            match = False;
            break;
        }
}


这是我的 MIPS 代码的一部分。

.text

# a0: text
# a1: substring
# v0: count
myfunction:
    move $s0, $ra

    move $a2, $a0
    jal  strlen
    move $t1, $v1           # text_len

    move $a2, $a1
    jal  strlen
    move $t2, $v1           # substring_len

    sub  $t1, $t1, $t2      # text_len - substring_len

    li   $t0, 0             # i = 0

    j i_test



i_body:
    li $t3, 1    # match = TRUE
    li $t4, 0    # j = 0

    j j_test

i_test:
    blt $t0, $t1, i_body
    move $ra, $s0
    jr $ra



j_body:
    add $t6, $a0, $t0       # &text[i]
    add $t6, $t6, $t4       # &text[i+j]
    lb  $t6, 0($t6)         # text[i+j]

    add $t7, $a1, $t4       # &sub_string[j]
    lb  $t7, 0($t7)         # sub_string[j]

    beq $t6, $t7, j_skip    # if (text[i+j] == sub_string[j])

    # if (text[i+j] != sub_string[j])
    li  $t3, 0              # match = FALSE
    j   j_break             # break

j_test:
    blt $t4, $t2, j_body

j_skip:
    addi $t4, $t4, 1    # j++
    j    j_body

j_break:
    addi $t0, $t0, 1    # i++
    j    i_body



strlen:
    li $v1, 0           # i = 0
    b strlen_test
strlen_body:
    addi $v1, $v1, 1    # len++
strlen_test:
    add $t0, $a2, $v1           # &str[i]
    lb $t0, 0($t0)              # str[i]
    bne $t0, $0, strlen_body    # loop
    jr $ra




.globl main
main:

    la $a0, text1
    la $a1, substring1
    jal myfunction
    la $a0, text1
    jal print_string

    li  $v0, 10         # Exit
    syscall


print_string: 
          li    $v0, 4
          syscall
          la    $a0, newline
          li    $v0, 4
          syscall
          jr    $ra


.data
text1:      .asciiz "Hello, world!"
substring1: .asciiz "lo"

newline:    .asciiz "\n"


但是，当我运行这段代码时，我得到了这个坏的无限循环

地址错误：


Exception occurred at PC=0x00400070                                                 
Bad address in data/stack read: 0x10021778                                                                                                                           
  Exception 7  [Bad address in data/stack read]  occurred and ignored                                                                                                    
Exception occurred at PC=0x00400078                                                                                                                                      
  Bad address in data/stack read: 0x10021786                                                                                                                             
  Exception 7  [Bad address in data/stack read]  occurred and ignored                                                                                                    
Exception occurred at PC=0x00400070                                                                                                                                      
  Bad address in data/stack read: 0x10021779                                                                                                                             
  Exception 7  [Bad address in data/stack read]  occurred and ignored                                                                                                    
Exception occurred at PC=0x00400078                                                                                                                                      
  Bad address in data/stack read: 0x10021787                                                                                                                             
  Exception 7  [Bad address in data/stack read]  occurred and ignored                                                                                                    
Exception occurred at PC=0x00400070                                                                                                                                      
  Bad address in data/stack read: 0x1002177a                                                                                                                             
  Exception 7  [Bad address in data/stack read]  occurred and ignored                                                                                                    
Exception occurred at PC=0x00400078                                                                                                                                      
  Bad address in data/stack read: 0x10021788                                                                                                                             
  Exception 7  [Bad address in data/stack read]  occurred and ignored                                                                                                    
Exception occurred at PC=0x00400070                                                                                                                                      
  Bad address in data/stack read: 0x1002177b                                                                                                                            
  Exception 7  [Bad address in data/stack read]  occurred and ignored                                                                                                    
Exception occurred at PC=0x00400078                                                                                                                                      
  Bad address in data/stack read: 0x10021789                                                                                                                             
  Exception 7  [Bad address in data/stack read]  occurred and ignored


我意识到错误的地址错误来自第 3 行和第 5 行

j_body（加载字节指令）。我已经初始化了字符串地址，所以我不确定这是为什么

发生...

以下是我的问题：

  1. 为什么我得到这个无限循环？（我以为我已经正确实现了 i 和 j 的 for 循环）

  2. 为什么我收到错误的地址错误？

谢谢 ：）

4

2 回答 2

2 
j_test:
    blt $t4, $t2, j_body

j_skip:
    addi $t4, $t4, 1    # j++
    j    j_body

j_break:
    addi $t0, $t0, 1    # i++
    j    i_body

j_break如果条件j_test失败，您不应该跳到吗？现在编写这段代码的方式，你继续执行“j循环”的主体，即使j >= strlen(substring).

此外，j i_body之后j_break:可能应该是j i_test（你已经增加i了，所以你需要检查“i 循环”的条件是否仍然为真）。

于 2013-11-09T20:29:19.493 回答
1

在 j_body 中，您使用 $t7 来存储 str(i+j) 和 sub_str(j); 然后通过比较 beq $t7, $t7, j_body 来决定是否退出 j_body （这条指令本身总是会评估为真，并使其成为无限循环）。将来自 sub_str(j) 的字节存储在 $t8 中，并将 beq 行更改为比较 $t7 和 $t8。

可能还有更多；但这绝对必须改变。更正此问题后，我建议运行，并使用您遇到的任何新错误更新您的问题。

于 2013-11-09T20:24:59.793 回答