Question

C3. Convert the following C-code to MIPS code. [Use register $al for the variable i, temporary registers for other values, and load the base memory address of the array OxA0000080 to Şao] int i i int array [101; for (i= 0; i<5 ; i=i+1 ) { [i+1] [i] 8; * array = array

Answer 1

Let's first take a look directly at the converted MIPS code.

1) # i -> $a1

2) # array address -> $a0

3) # to hold immediate value 8 -> $t3

3) .globl main

4) main:

5) li $a1, 0

6) la $a0, 0xA0000080

7) loop:

8) bgt $a1, 4, exit

9) lw $t1, 0($a0)

10) mul $t2, $t1, $t3

11) sw $t2, 4($a0)

12) addi $a0, $a0, 4

13) addi $a1, $a1, 1

14) j loop

15) exit:

Now let's move through the code and see how it works.

First three lines are comments indicating which register is used to store what.

4), 7) and 14) are labels which help to branch from one part to another.

5) 'li' loads immediate value '0' to register '$a1'

6) 'la' loads address '0xA0000080' to $a0

8) 'bgt' branches to label 'exit' i.e line 14 if $a1 is greater than 4, else it continues to next statement. 'bgt' stands for branch if greater than.

9) loads value at address in $a0 register to register $t1 i.e. first element of array.

10) multiplies the element with 8 (stored in $t3) and stores the result in temporary register $t2. i.e. value of 'array[i]*8'. This is to be stored in the next location of the array according to the C code.

11) stores the value ($t2) to the memory address specified as '$a0 + 4' i.e. next memory location (represented as '4($a0)' in MIPS assembly syntax).

12) now the address in $a0 is increased by 4 i.e. it's made to point to the next memory location so that the next iteration of the loop can deal with the next set of values of the array.

13) the loop variable 'i' value is incremented i.e. $a1 register is incremented.

14) the statement execution jumps to 'loop' label. and the next iteration starts.

This repeats until the value $a1 register (i value) increases to 5 upon which the 'bgt $a1, 4, exit' statement will branch to 'exit' label and the program will end. This means the loop will repeat 5 times $a1 register will vary from 0 to 4, at the end of which the array in memory will have gotten modified as per the description in the C code.

Hope this Helped :) All the best.