Question

Write a function (subroutine) that inputs a data value in register r0 and returns value in r0. The function returns y 5 a 1 bx 1 cx2, where a, b, and c are parameters built into the function (i.e., they are not passed to it). The subroutine also performs clipping. If the output is greater than a value d, it is constrained to d (clipped). The input in r0 is a positive binary value in the range 0 to 0xFF. Apart from r0, no other registers may be modified by this subroutine. Write ARM code to implement the following C operation.
Int s=0;
for ( i = 0; i < 10; i++) { s = s + i*i;)

Answer 1

Solution :

  int f(int x){

      $\text{return a + b*x +c*x*x}$;

  }*/

  int f($\text{int R0}$){

      int stack[2] = {$\text{R1,R2}$};

      $\text{R1 = R0}$;

      $\text{R1 = R1}\times \text{ R1}$;

      $\text{R2 = C}$;

      R1 = R1 * C; /*R1 = $cx^2$*/

      $\text{R2 = B}$;

      $\text{R0 = R0}$ * R2; /* R0 = bx */

      $\text{R0 = R0 + R1}$; /*R0 = $bx + cx^2$ */

      $\text{R2 = C}$;

      $\text{R0 = R0 + R2}$; /*R0 = a+bx+cx^2 */

      $\text{R1 = stack[0];}$

     $\text{ R2 = stack[1];}$

     $\text{ return R0;}$

  }

  /*$\text{ARM code to implement the following C operation}$

  int s=0;

  $\text{for ( i = 0; i < 10; i++)}$

  { $\text{s = s + i } \times i$;)

  */

          AREA SumSquares, code, readWrite

          ENTRY

          $\text{MOV r0, #0}$        ;loop $\text{ counter i present at 0}$

          MOV r1, #0       ; s = 0

  Loop   $\text{MUL r2, r0, r0}$   ;calculate i*i

          $\text{ADD r1, r1, r2}$   ;s = s+ i*i

          $\text{ADDS r0, r0}$, #1   ; i = i+1

          $\text{CMP r0}$,#10       ; test for end

          $\text{BNE}$ Loop        ; $\text{continue until all added}$

          END