Question

Write a program in "RISC-V" assembly to convert an ASCII string containing a positive or negative integer decimal string to an integer. ‘+’ and ‘-’ will appear optionally. And once they appear, they will only appear once in the first byte. If a non-digit character appears in the string, your program should stop and return -1.

Answer 1

Source Code:

.data

String:         .asciz "1234\n"
Show_integer:   .asciz  "The integer = %d\n"
Intg:           .long 0

.text
.global main

main:   
        movl    $1, %edi
        movl    $0, %ebx
        movl    $String, %ecx

character_push_loop:
        
        movb    (%ecx), %dl     /*Take one byte from the string and put in %dl*/
        cmpb    $0, %dl
        je      conversion_loop
        movb    %dl, (%eax)
        pushl   %eax            /*Push the byte on the stack*/
        incl    %ecx
        incl    %ebx
        jmp     character_push_loop

conversion_loop:
        popl    %eax
        subl    $48, %eax       /*convert to ASCII number*/
        imul    %edi            /* eax = eax*edi */
        addl    %eax, Intg
        movl    $10, %eax
        movl    %edi, %eax
        imul    %ecx            /* eax = eax*ecx */
        movl    %eax,%edi       /* edi = eax */
        decl    %ebx
        cmpl    $0, %ebx
        je      end             /*When done jump to end*/
        jmp     conversion_loop

end:            
        pushl   Intg
        pushl   $Show_integer
        call    printf          /*Print out integer*/
        addl    $8, %esp
        call    exit

Let me know if you have any doubts or if you need anything to change. 

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Thank You!
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