convert c to mips assembly language

Question

I am trying to convert some instruction to MIPS code. But have no idea how to do that.. i know c language so i can decode it to C but dont know how to convert it to MIPS.

1. I need to write a main
2. create an array of 10 integers
3. Declare a variable
4. make a loop to check if it is odd or even
5. print a string saying "it is odd or it is even creating if else statement
6. and increment the variable.

I can write C program for these. But what would it be in MIPS?

int main()
{
  int array[10]={1,2,3,4,5,6,7,8,9,10};
  int i=0;
  while(i<10){
    if(i%2==0)
      printf("It is even\n");
    else
      printf("it is odd\n");
    i=i+1;
  }
  return 0;
}

Answer 1

Have you tried compiling it with gcc on MIPS?

Answer 2

Use mips_gcc -S test.c ,the generated assemble code is test.s.

Or you can

    mips_gcc -o test -g test.c
    mips_objdump -Sd test > test_2.s

Compared with the first method , the latter has some benifit :

• the register is in the form of $v0 ,v$1 instead of $0 , $1
• you can cross refer to the C code

see the comparison:

     #test.s       - use gcc -S 
    .frame  $fp,24,$31              # vars= 8, regs= 1/0, args= 0, gp= 8
    .mask   0x40000000,-8
    .fmask  0x00000000,0
    .set    noreorder
    .set    nomacro

    addiu   $sp,$sp,-24
    sw      $fp,16($sp)
    move    $fp,$sp
    sw      $0,12($fp)
    li      $2,24                   # 0x18
    sw      $2,8($fp)
    li      $2,3                    # 0x3
    sw      $2,12($fp)
    lw      $3,12($fp)
    lw      $2,8($fp)


 #test_2.s   - use objdump -Sd
 4005c0:   27bdffe8    addiu   sp,sp,-24
 4005c4:   afbe0010    sw  s8,16(sp)
 4005c8:   03a0f021    move    s8,sp
 int a = 0;
 4005cc:   afc0000c    sw  zero,12(s8)
 int b = 24;
 4005d0:   24020018    li  v0,24
 4005d4:   afc20008    sw  v0,8(s8)
 a = 3 ;
 4005d8:   24020003    li  v0,3
 4005dc:   afc2000c    sw  v0,12(s8)
a += b; 
4005e0:   8fc3000c    lw  v1,12(s8)
4005e4:   8fc20008    lw  v0,8(s8)
4005e8:   00000000    nop

Answer 3

> .txt
.globl main
main:
array: .word 0:10 #array of 10 integers

li $s0,0
li $1,10

begin: 
slt $t0,$s0,$s1
bne $t0, $zero,while

while:

Answer 4

Here is some stuff to think about.

Calls to printf: Those involve calling the system call write. Depending on what you want to do, you have 2 choices

• Call printf function
• Call write system call via syscall instruction.

compiler generated code and @pierr shows will call printf.

IF you want to work in mips in a "more real than spim or mars" environment, I recommend gxemul. You can simulate a netbsd running on mips.

Inside there, you have gcc, gdb, the works.

So, getting the assembly code of your main function (i.e not objdump) is really easy.

$gcc -S -mrnames main.c

The rest, is quite simple. As you are not asking for a mips to C translation, i'm not going to write the mips code, but will give you some tips.

int i=0;

Ok, this is a WORD, with the value 0x0. In mips, you have a special register ($0) called $zero,which is hardcoded to the 0 value. So to load a variable with 0x0, you have to alternatives.

mv $t1,$zero

or

li $t1,0

(there are more, such as subu $t1,t1,t1, but that's reinventing the wheel)

Then, you have your while loop.

Check your i variable ($t1). You'll have to use a branch instruction for that. Just load the 10 value in another register, and jump to a label according to the result.

Now, loading the array element. THis is the tricky part. That array is NOT in mains stack. Its defined like this.

.rdata
.align 2
$array: .word 1
        .word 2
        .word 3
        //you get the picture right?
main: //main function starts here.

The address of the first element of the array is $array (great isnt it?).

So to load the first (or the nth for that matter) element, just

   la $t3,$array #this load the address of the array into $t3 register
   lw $t2,0($t3) #this does $t2= *(array+0)

So now $t2 contains your array element.

The mod part is REALLY easy. As you are "modding" against 2, you can just take the lsb from your array element, something like

andi $t2,$t2,0x1

Now $t2 contains 1 if the number is odd (lsb is 1) or 0 if its even (lsb is 0). To compare, again, a branch instruction.

When you are done, increment your i variable (use one of the add instructions on t1) and branch back to the comparison.

The return is easy. Return values usually goes in $v0 register (this depends though)

 li $v0,0
 jr $ra

Answer 5

try the C/C++ to MIPS Assembly converter at http://ctomips.com. Let me know what you think!