I’m trying to write a procedure in assembly that sorts an array using bubble-sort algorithm but I’m having a problem which is:
In line 22, when the first iteration executed nothing is wrong, program loads array[i+1] perfectly into registrar $a1 and if the swap condition is valid, program swaps without any problem. However, in the second iteration, program always loads 0 into $a1 whatever the real value of the element was! I tried debugging it but nothing was clear and I don’t know what is the cause of this.
1. # Procedure: bubbleSort 2. # Objective: sort an array of integer elements in nondecreasing order 3. # Input: an address of an array of integers 4. # Output: an array sorted in nondecreasing order 5. 6. bubbleSort: 7. 8. move $t0, $a0 # move address of the array into $t0 9. li $s0, 1 # boolean swap = false. 0 --> false, 1 --> true 10. li $t1, 0 # j = 0; 11. li $t2, 0 # i = 0; 12. li $s1, 9 # array length 13. loop: 14. beqz $s0, exit # exit if swap = false 15. li $s0, 0 # swap = false; 16. addiu $t1, $t1, 1 # j++; 17. move $t2, $0 # i = 0; 18. subu $s2, $s1, $t1 # s2 = length - j 19. forLoop: 20. bge $t2, $s2, exitForLoop # if i>=s2, exit 21. lw $a0, 0($t0) # a0 = array[i] 22. lw $a1, 4($t0) # a1 = array[i+1] 23. ble $a0, $a1, update # if array[i]<=array[i+1] skip 24. sw $a1, 0($t0) # a[i+1] = a[i] 25. sw $a0, 4($t0) # a[i] = a[i+1] 26. li $s0, 1 # swap = true; 27. update: 28. addiu $t2, $t2, 1 # i++ 29. sll $t3, $t2, 2 # t3 = i*4 30. addu $t0, $t0, $t3 # point to next element --> 31. j forLoop 32. exitForLoop: 33. j loop 34. exit: 35. jr $ra