assignment.asm

.MODEL SMALL
.DATA
    NUMBERS DB 4 DUP (?)
    J DW 1
    I DW ?
    LINEBREAK DB 10, 13, "$"
    KEY DB ?
    
    MSG1 DB "Ascending Order: $"
    MSG2 DB "Descending Order: $"
.CODE
    MOV AX, @DATA
    MOV DS, AX

    ; take input of 4 numbers
    MOV CX, 4
    MOV AH, 1
    LEA SI, NUMBERS
    L1:
        INT 21h
        MOV [SI], AL
        INC SI
    LOOP L1
    
    ; line break
    MOV AH, 9
    LEA DX, LINEBREAK
    INT 21h
    
    ; sort the numbers
    MOV CX, 3
    L3:
        ; key = A[j]
        LEA SI, NUMBERS
        ADD SI, J
        MOV BH, [SI]
        MOV KEY, BH
        
        ; i = j - 1
        MOV DX, J
        MOV I, DX
        DEC I
        
        PREPREWHILE:
            ; i > 0
            CMP I, 0
            JGE PREWHILE
            JNGE AFTERWHILE
        
        PREWHILE:
            ; A[i] => BH
            LEA SI, NUMBERS
            ADD SI, I
            MOV BH, [SI]
            
            ; A[i] > key
            CMP BH, KEY
            JG WHILE
            JNG AFTERWHILE
            
        WHILE:
            ; A[i] => BH
            LEA SI, NUMBERS
            ADD SI, I
            MOV BH, [SI]
        
            ; A[i + 1] = A[i]
            LEA SI, NUMBERS
            ADD SI, I
            INC SI
            MOV [SI], BH
            
            DEC I
            JMP PREPREWHILE
            
        AFTERWHILE:
            ; A[i + 1] = key
            LEA SI, NUMBERS
            ADD SI, I
            INC SI
            MOV BH, KEY
            MOV [SI], BH
            
            INC J
    LOOP L3
    
    ; ascending order
    MOV AH, 9
    LEA DX, MSG1
    INT 21h
    
    MOV CX, 4
    LEA SI, NUMBERS
    MOV AH, 2
    L2:
        MOV DL, [SI]
        INT 21h
        INC SI
    LOOP L2
    
    ; line break
    MOV AH, 9
    LEA DX, LINEBREAK
    INT 21h
    
    ; descending order
    MOV AH, 9
    LEA DX, MSG2
    INT 21h
    
    MOV CX, 4
    LEA SI, NUMBERS
    ADD SI, CX
    MOV AH, 2
    L4:
        DEC SI
        MOV DL, [SI]
        INT 21h
    LOOP L4