Descending bubblesort with 68k

Question

i'm learning Assembly on Motorola 68k, i was able to do BubbleSort in ascending order but not descending, i don't know why the program goes into infinite loop; Thx;: The code:

  ORG  $2000
  START LEA  ARRAY,A0
  CLR  D0 *Flag di scambio      
  MOVE.B #L-1,D1 *contatore      
  LOOP  MOVE.B (A0),D2
  MOVE.B 1(A0),D3
  CMP    D2,D3
  BLE    ELSE
  MOVE.B D2,1(A0)
  MOVE.B D3,(A0)
  MOVE.B #1,D0      
  ELSE  ADD  #1,A0
  DBRA D1,LOOP      
  TST D0
  BNE START
  SIMHALT
  ORG  $1000
  ARRAY DC.B 1,5,2,4,3
  L     EQU  5           
  END  START  

Answer 1

      MOVE.B #L-1,D1 *contatore      
LOOP  MOVE.B (A0),D2
      MOVE.B 1(A0),D3
      CMP    D2,D3
      BLE    ELSE
      MOVE.B D2,1(A0)
      MOVE.B D3,(A0)
      MOVE.B #1,D0      
ELSE  ADD    #1,A0
      DBRA   D1,LOOP

Your loop that is based on the D1 contatore runs for too long, In an array that has 5 elements. you can do at most 4 comparisons. That's why you wrote #L-1 . However the DBRA instruction repeats until the count is -1 , so in this case you still get 5 iterations which is 1 too many.

i don't know why the program goes into infinite loop;

An infinite loop could result from not having initialized the whole 16-bit counter for the DBRA D1,LOOP instruction! Better use MOVE.W #L-1,D1 .

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When the non-zero D0 register tells you that a change was made to the array, you repeat the whole code. That can work ok, but it is more efficient to realize that the smallest element will have bubbled to the far end and need not be processed any more. The solution is to have a variable contatore instead of the constant #L-2 (after correction).

START MOVE.W #L-2,D4   *first_contatore

NEXT  LEA    ARRAY,A0
      CLR    D0        *Flag di scambio      
      MOVE.W D4,D1     *contatore      
      
LOOP  ...
      ...
      DBRA   D1,LOOP
      TST.B  D0
      BEQ    DONE      *Nothing was changed, earliest exit
      DBRA   D4,NEXT

DONE  SIMHALT