can someone help me convert this C code to MIPS assembly? I keep getting an infinte loop.

C code:

uint32_t reverse_sum(uint32_t *arr) {
  uint32_t r;

  if(*arr == -1) return 0;
  r = reverse_sum(arr 1)   (uint32_t)*arr;
  *arr = r;        
  return(r);
}

This is what I tried, I see why I am getting an infinite loop, but I can't think of another approach to this without getting an infinite loop. (Assume $a0 holds the arr, and $v0 is the return register).

reverse_prefix_sum:
   # PROLOGUE
   subu $sp, $sp, 8        # expand stack by 8 bytes
   sw   $ra, 8($sp)        # push $ra (ret addr, 4 bytes)
   sw   $fp, 4($sp)        # push $fp (4 bytes)
   addu $fp, $sp, 8        # set $fp to saved $ra

   lw $t0, 0($a0)          # t0 now stores first array element

   bne $t0, -1, rec        
   li $v0, 0               
   j ret                   

rec:
   subu $sp, $sp, 4        # expand stack by 1 spot 
   sw $t0, 4($sp)          # store t0 (first element in array) on the stack
   lw $a0, 4($a0)          # load arr   1 element in a0
   jal reverse_prefix_sum
   lw $a0, 4($sp)
   add $t1, $v0, $a0
   sw $t1, 0($t0)
   move $v0, $t1 


ret:
   # EPILOGUE
   move $sp, $fp           # restore $sp
   lw   $ra, ($fp)         # restore saved $ra
   lw   $fp, -4($sp)       # restore saved $fp
   jr   $ra                # return to kernel

CodePudding user response：

That has this instruction:

lw $a0, 4($a0)          # load arr   1 element in a0

to pass a pointer parameter to the recursive function

But the C code wants a pointer to the element, not an array element value.  To pass arr 1 you merely need an add instruction, not a load.

In C, arr 1 is a pointer arithmetic expression, not a dereference.