Question

Two arrays “Array1” and “Array2” are given with 25 words each. Design an ARM assembly code to compare sum of the numbers sotred in the arrays. If sum of Array1 is greater, save a “1” in R10, otherwise, save “0’ in R10.

Answer 1

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******* ARM Code **********

ENTRY ; /*starting of program*/
  LDR r2, LENGTH ; /*length of the array(=25)*/
  SUB r2, r2, #1 ; /*r2 contains (LENGTH-1) */
  MOV r6, #0 ; /*r6 sum set to 0 */
FOR_INIT MOV r1, #0 ; /*r1 index I set to 0 forA[I]*/
  ADR r3, ARRAY1 ; /*start r3 with address of A[0] */
FOR_CMP CMP r1, r2 ; /*compare I and (LENGTH-1) */
  BGT END_FOR ; /*drop out of loop if I < (LENGTH-1) */  
  LDR r4, [r3],#4 ; /*load r4 with A[I] then walk r3 down ARRAY */
  ADD r6, r6, r4 ; /*update sum with A[I] */
  ADD r1, r1, #1 ; /*increment I */
  B FOR_CMP ; /*loop back to for-loop check */
END_FOR
  STR r6, SUM1; /*store result in SUM1 */

  /*****   the second array summing operation ******/

   LDR r2, LENGTH ; /*length of the array(=25)*/
  SUB r2, r2, #1 ; /*r2 contains (LENGTH-1) */
  MOV r6, #0 ; /*r6 sum set to 0 */
FOR_INIT MOV r1, #0 ; /*r1 index I set to 0 forA[I]*/
  ADR r3, ARRAY2 ; /*start r3 with address of A[0] */
FOR_CMP CMP r1, r2 ; /*compare I and (LENGTH-1) */
  BGT END_FOR ; /*drop out of loop if I < (LENGTH-1) */  
  LDR r4, [r3],#4 ; /*load r4 with A[I] then walk r3 down ARRAY */
  ADD r6, r6, r4 ; /*update sum with A[I] */
  ADD r1, r1, #1 ; /*increment I */
  B FOR_CMP ; /*loop back to for-loop check */
END_FOR
  STR r7, SUM2; /*store result in SUM2*/

  CMP r6,r7;
  BLT     R6_lower   /* jump to R6_lower in case R7 is bigger */
  MOV r10, #1     /* if not, save 1 to R10*/
  B STOP

R6_lower:
          MOV r10, #0        /* save 0 to R10*/
  B STOP

STOP   B STOP

********* End of code ************