Tryig to translate C code to MIPS assembly to work on spim

Question

i wrote a code for computing factorial on C, however im trying to translate it to assembly language to work on PCspim but have no idea how?? can someone help please?

C code:

 #include <stdio.h>

 #include <stdlib.h>

 #include <string.h>

void factorial(long argument, long *result) {

    if(argument < 2) {
    printf("%ld", *result);
    } else {
        long before = argument - 1;
        *result = *result * before;
        argument = before;
      factorial(argument, result);
         }
}

 int main() {

   long argument, answer, *result;

   printf("Factorial ");

   scanf("%ld", &argument);

   result = &answer;

   *result = argument;

   printf("%ld! = ",argument);

   factorial(argument, result);
 }

Answer 1

SPIM is a MIPS interpreter, so you'll have to write those procedures in MIPS assembly... You might take a look at the output of

gcc -s <filename>

, which produces assembly representations, however I suspect it is limited to the architecture upon which you are running GCC (likely X86. X86 != MIPS).

When I had to write MIPS assembly for my Fundamentals course a few weeks ago I made heavy use of the Wikipedia article and the following website: http://en.wikibooks.org/wiki/MIPS_Assembly/Arithmetic_Instructions

Answer 2

Are you writing the factorial from scratch, or 'compiling' the C code? two very different approaches.

When I did some RISC coding, I found it best to pseudocode it out and implement it directly without reference to C.

If you are compiling, then each C statement needs to be expanded out to the equivalent RISC assembly.

edit: Here is some information: A page from U of Idaho's course that uses MIPS/spim.

Answer 3

I wrote a compiler that does it for fun, with a subset of C to SPIM asm syntax (of course recursion is supported)..

According to it

int f(int x) 
{
  if (x == 1)
       return 1;
    else
     return (x*f(x-1));
}

int main (void) {
  f(8);
}

compiles to

    .data
.align 4
.align 1

    .text
    .globl main
main:
    subu $sp, $sp, 32
    sw $ra, 20($sp)
    sw $fp, 16($sp)
    addiu $fp, $sp, 28
    li $t6, 8
    move $a0, $t6
    jal f
    lw $ra, 20($sp)
    lw $fp, 16($sp)
    addu $sp, $sp, 32
    jr $ra

f:
    subu $sp, $sp, 36
    sw $ra, 24($sp)
    sw $fp, 20($sp)
    addiu $fp, $sp, 32
    li $t0, 1
    bne $a0, $t0, equal0
    li $t1, 1
    b equal1
equal0:
    li $t1, 0
equal1:
    li $t2, 0
    beq $t1, $t2, if2
    li $v0, 1
    lw $ra, 24($sp)
    lw $fp, 20($sp)
    addu $sp, $sp, 36
    jr $ra
    b if3
if2:
    li $t3, 1
    subu $t4, $a0, $t3
    sw $a0, 0($sp)
    move $a0, $t4
    jal f
    move $t5, $v0
    lw $a0, 0($sp)
    mulou $v0, $a0, $t5
    lw $ra, 24($sp)
    lw $fp, 20($sp)
    addu $sp, $sp, 36
    jr $ra
if3:
    lw $ra, 24($sp)
    lw $fp, 20($sp)
    addu $sp, $sp, 36
    jr $ra

Try if it works, it's not optimized at all but you can get a clue and modify it according to your needs..