输入验证 MIPS

Question

如何使用 MARS 验证 MIPS 指令集中的用户输入？在我的以下程序中，我想知道如何向用户输入添加验证，例如，当询问用户是否要解密或加密他们需要输入 'E' 或 'D'（区分大小写）的消息时由于 ascii 值）。以及来自 (1-9) 的输入，它是加密或解密密钥。如果他们输入 'E'、'D' 和 1-9 以外的任何数字，我如何要求用户使用每个提示的子例程输入有效输入？

代码：

.data
    encrypt_decrypt: .asciiz "Type(E)ncrypt/(D)ecrypt:"
    key: .asciiz "\nEnter encryption key (1-9): "
    message_prompt: .asciiz "\nEnter message: "
    output: .asciiz ""
    re_enter: .asciiz "\nWrong input"
    buffer: .space 50
.text

main: 
    # Prints the prompt asking the user if they want to encrypt or decrypt
    li $v0, 4
    la $a0, encrypt_decrypt # Loads address from the user prompt
    syscall

    # Takes in E OR D based on user choice
    li $v0, 12      
    syscall
    add $t6, $v0, [=10=]    
    bne $t6, 69, ELSE # Branch to else if inputed value is not E

    # Prints the prompt asking the user for a message to either decrypt or 
    encrypt based on the users previous choice
    li $v0, 4
    la $a0, message_prompt # Loads address from the users message
    syscall

    # Takes the users message
    li $v0, 8
    la $a0, buffer
    lb $t0, 0($a0)
    li $a1, 48
    syscall
    la $s2, buffer

    # Asks the user for a key from 1-9
    li $v0, 4
    la $a0, key
    syscall


    # Takes the users key value from 1-9
    li $v0, 5
    syscall
    add $s0, $v0, [=10=]    

    la $t0, ($s0)   # Loads key
    li $t1, 0       # Lower order bit to be toggled
    la $t2, ($s2)   # Load user message


    beq $t6, 69, encrypt # 69 Is the printable ASCII value of "E"
    beq $t6, 68, decrypt # 68 is the printable ASCII value of "D"
ELSE:
    bne $t6, 68, E_D_VALIDATION # Branch to E_D_VALIDATION if user input is not D

E_D_VALIDATION:
    li $v0, 4
    la $a0, re_enter
    syscall
    j main  

encrypt: 

encrypt_loop: 

    lb   $t3, 0($t2)        # Loads character bytes
    beq  $t3, 10, encrypted # Branches to "encrypted" if we reach the end of a character
    add  $t3, $t3, $t0
    addi $t4, [=10=], 1       
    sllv   $t4, $t4, $t1    
    xor   $t3, $t3, $t4     # Lower order bit toggle

    sb   $t3, 0($t2)        # Stored encrypted character
    addi $t2, $t2, 1
    j encrypt_loop      # Loops through the list of encrypted characters
    
 encrypted:     
    li $v0, 4               # Print out encrypted message
    la $a0, output
    syscall
    la $a0, ($s2)
    syscall
    
    j exit              # Exits the program


decrypt: 
decrypted_loop:
    lb $t3, 0($t2)         # Loads character bytes
    beq $t3, 10, decrypted # Branches to "decrypted" if we reach the end of a character
    addi $t4, [=10=], 1
    sllv $t4, $t4, $t1
    xor $t3, $t3, $t4
    sub $t3, $t3, $t0
    sb $t3, 0($t2)        # Stored decrypted character
    addi $t2, $t2, 1

    j decrypted_loop      # Loops through the list of decrypted characters


decrypted: 
    li $v0, 4            # Print out decrypted message
    la $a0, output
    syscall
    la $a0, ($s2)
    syscall

    j exit              # Exit the program


    exit:

Answer 1

您所缺少的只是错误处理：

    beq $t6, 69, encrypt # 69 Is the printable ASCII value of "E"
    beq $t6, 68, decrypt # 68 is the printable ASCII value of "D"

    <handle error here>
     
encrypt:

如何处理错误：打印一条消息并退出，或者打印一条消息并转到代码中较早的位置，可能 main 或您为此引入的其他一些新标签。

但是，在进行到这里之前检查是否有错误输入可能会很好，如果你这样做了，你以后就不必再检查那么久了：你可以只检查 E 或只检查 D，而不是同时检查两者，因为在这一点上你知道它只是其中之一，没有别的。

所以你想在输入 E 或 D 后立即输入的伪代码：

if ( input != E && input != D ) { print input error message; goto reEnter; }

其中 reEnter 可能是主要位置或您选择返回以获取输入的其他位置。

我会使用以下一系列转换将其翻译成汇编语言。

首先，if-goto-label 样式，当条件为假时跳过 if 语句的 then 部分：

    if ( ! ( input != E && input != D ) ) goto inputOk;
    print input error message
    goto reEnter;
inputOk:
    ; continue with rest of program knowing good input (exactly E or D)

接下来：根据 De Morgan:

分配否定

    if ( ! ( input != E ) || ! ( input != D ) ) goto inputOk;
    print input error message
    goto reEnter;
inputOk:
    ; continue with rest of program knowing good input (exactly E or D)

下一步：取反关系运算符：

    if ( input == E || input == D ) goto inputOk;
    print input error message
    goto reEnter;
inputOk:
    ; continue with rest of program knowing good input (exactly E or D)

下一步：拆分析取(||)

    if ( input == E ) goto inputOk;
    if ( input == D ) goto inputOk;
    print input error message
    goto reEnter;
inputOk:
    ; continue with rest of program knowing good input (exactly E or D)

现在，用汇编写起来很容易。

输入验证 MIPS

Input Validation MIPS

validation

user-input

mips