需要帮助对 MIPS 代码进行故障排除以计算小写字母

Question

我用 MIPS 编写了这段代码来计算用户输入的小写字母的数量：

.data
msg1: .asciiz
count_lower: .space 41
.text
.globl main
main:
la $a0, msg1 #load address of msg1 to store string
li $a1, 100 #msg1 is 100 bytes
li $v0, 8 #syscall for read str
syscall

add $s1, [=10=], [=10=] #interger to print later
la $t0, count_lower 
sw $a0, 0($t0) #store input string in $t0
loop:
lb $t1, 0($t0) #load char from $t0
beqz $t1, exit #if no more chars, exit
blt $t1, 'a', else #This line and line below are for if char is not lowercase
bgt $t1, 'z', else
addi $s1, $s1, 1 #if char is lowercase, +1 to $s1
sll $t0, $t0, 8 #shift one byte to get to next char
sll $t1, $t1, 8 #shift one byte to get to next char

else:
sll $t0, $t0, 8 #shift one byte to get to next char
sll $t1, $t1, 8 #shift one byte to get to next char
j loop #jump back to loop

exit:
move $a0, $s1 #move interge to print into $a0
li $v0, 1 #print interger in $a0
syscall
li $v0, 10 #exit 
syscall

但是当我运行它时，无论输入什么字符串，它都会打印整数“0”。谁能帮我解决问题？我在代码中写了注释来解释我的思考过程。

编辑：

1 .data
2 msg1: .space 100
3 .text
4 .globl main
5 main:
6 li $v0, 8 #syscall for read str
7 la $a0, msg1 #load address of msg1 to store string
8 li $a1, 100 #msg1 is 100 bytes
9 move $t0, $a0 #save user input to $t0
10 syscall
11 add $s1, [=11=], [=11=] #interger to print later
12 add $t1, [=11=], [=11=] #initialize $t1
13 loop:
14 sb $t0, 0($t1) #store rightmost char into memory 0
15 lb $t1, 0($t0) #load char from memory 0 into $t1
16 beqz $t1, exit #if no more chars, exit
17 blt $t1, 'a', else #This line and line below are for if char is not       
18 lowercase
19 bgt $t1, 'z', else
20 addi $s1, $s1, 1 #if char is lowercase, +1 to $s1
21 srl $t0, $t0, 8 #shift one byte to get to next char
22 add $t1, [=11=], [=11=] #re-initialize $t1
23 j loop #jump back to loop
24 else:
25 srl $t0, $t0, 8 #shift one byte to get to next char
26 add $t1, [=11=], [=11=] #re-initialize $t1
27 j loop #jump back to loop
28 
29 exit:
30 move $a0, $s1 #move interge to print into $a0
31 li $v0, 1 #print interger in $a0
32 syscall
33 li $v0, 10 #exit 
34 syscall

Answer 1

这并不像您认为的那样：

sw $a0, 0($t0) #store input string in $t0

该指令仅存储字符串的 地址 ($t0)（即 count_lower 的前 4 个字节）。

我真的不明白你为什么需要两个缓冲区。只需从您为系统调用 8 指定的同一缓冲区中读取字符。

此外，您的 msg1 声明不正确。你的评论说 #msg1 is 100 bytes，但你的声明是 msg1: .asciiz，这肯定不会保留 100 个字节。那应该改为 msg1: .space 100.

需要帮助对 MIPS 代码进行故障排除以计算小写字母

Need help troubleshooting MIPS code to count lowercase letters

string

add

mips

char