我正在编写一个简单的MIPS汇编代码，用于遍历字符串的字符
并找到给定子字符串的实例..
首先，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，当我运行此代码时，我得到了这个无限循环的错误
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
的第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，所以我不确定为什么这是
...发生
以下是我的问题：
为什么我会得到这个无限循环？ （我以为我已经为i和j正确实现了for循环）
为什么我收到错误的地址错误？
谢谢：）
答案 0 :(得分：2)
j_test:
blt $t4, $t2, j_body
j_skip:
addi $t4, $t4, 1 # j++
j j_body
j_break:
addi $t0, $t0, 1 # i++
j i_body
如果j_break的条件失败，您是不是应该跳到j_test？现在编写此代码的方式即使j >= strlen(substring)也继续执行“j循环”的主体。
此外，j i_body之后的j_break:应该是j i_test（您已经增加了i，因此您需要检查“i循环”的条件“仍然是真的。”
答案 1 :(得分：1)
在j_body中，你使用$ t7来存储str（i + j）和sub_str（j）;然后决定是否通过比较beq $ t7，$ t7，j_body来退出j_body（此指令总是会评估为真，并使其成为无限循环）。将sub_str（j）中的字节存储在$ t8中，并将beq行更改为比较$ t7和$ t8。
可能会有更多;但这绝对必须改变。在你纠正这个之后，我建议你运行，并用你得到的任何新错误更新你的问题。