How do I split in Assembly?


good guys ,

I'm new to assembly, I'm having problems doing division. When I compile the program from the command line, I get this Floating point exception error.

.section .data

.global op1
.global op2
.global resultado

.section .text

.global Conta    



pushl %ebp    
movl %esp, %ebp   

movl op1, %edx
movl op2, %eax
divl %edx, %eax
movl %eax, resultado


movl %ebp, %esp  
popl %ebp   



The div instruction, divides the value (unsigned integer) stored in the pair of registers edx:eax (dividend – 64 bits) by the destination operator (can be a register or memory location – 32 bits), and stores the quotient in eax and the rest in edx .

Since you are storing the value of op1 in edx , and dividing edx:eax by edx (which is part of the dividend), the result of the division is probably greater than 32 bits and this generates the Floating point exception error (or divide error , as per the Intel manual ).

A possible solution to the problem is to reset the edx register and use a register other than edx and eax to store the divisor (if the division you are trying to do is 32 bits and not 64 bits).

Here is an example of your changed code, using the ebx register to store the divider:

        push %ebp
        movl %esp, %ebp
        movl op2, %ebx       # armazena o divisor em ebx
        xorl %edx, %edx      # zera edx (parte alta do dividendo)
        movl op1, %eax       # armazena o dividendo (parte baixa) em eax
        divl %ebx, %eax      # divide edx:eax por ebx
        movl %eax, resultado
        movl %ebp, %esp
        pop %ebp

Execution example: division 13 by 3:

Conta () at teste.a:30
30              movl op2, %ebx
31              xorl %edx, %edx
32              movl op1, %eax
33              divl %ebx, %eax
(gdb) info registers
eax            0xd      13      <----- parte "baixa" do dividendo
ecx            0x0      0
edx            0x0      0       <----- parte "alta" do dividendo
ebx            0x3      3       <----- divisor
(gdb) s
34              movl %eax, resultado
(gdb) info registers
eax            0x4      4       <----- quociente
ecx            0x0      0
edx            0x1      1       <----- resto
ebx            0x3      3
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