1.asm

binary to decimal converter

; input8 bit binary number and print out decimal to screen. 
; zeros and ones -> decimal value 

ORG 100h

; this macro prints a char in AL and advances 
; the current cursor position: 
PUTC    MACRO   char
        PUSH    AX
        MOV     AL, char
        MOV     AH, 0Eh
        INT     10h
        POP     AX
ENDM

.data
; null terminated input string: 
DB "0"
s1 DB "00000000", 0
sum DW 0  ; result. 
flag DB 0


.code
CALL print
DB 0dh, 0ah, "8 bit binary: ", 0



; get string: 
MOV DX, 9   ; buffer size (1+ for zero terminator). 
LEA DI, s1
CALL GET_STRING


; check that we really got 8 zeros and ones 
MOV CX, 8
MOV SI, OFFSET s1
check_s:
        CMP [SI], 0
        JNE ok0
        MOV flag, 1     ; terminated. 
        JMP convert
    ok0:
        CMP [SI], 'b'
        JNE ok1
        MOV flag, 1     ; terminated. 
        JMP convert
    ok1:
        ; wrong digit? Not 1/0? 
        CMP [SI], 31h
        JNA ok2
        JMP error_not_valid
    ok2:
        INC SI
    LOOP check_s







; start the conversion from string to value in SUM variable. 
convert:
MOV BL, 1   ; multiplier. 
MOV CX, SI
SUB CX, OFFSET s1
DEC SI

JCXZ stop_program

next_digit:
    MOV AL, [SI]  ; get digit. 
    SUB AL, 30h
    MUL BL      ; no change to AX. 
    ADD SUM, AX
    SHL BL, 1
    DEC SI          ; go to previous digit. 
    LOOP next_digit

; done! converted number is in SUM. 

; check if signed 
TEST sum, 0000_0000_1000_0000b
JNZ  print_signed_unsigned

print_unsigned:
CALL print
DB 0dh, 0ah, "decimal: ", 0
MOV  AX, SUM
CALL PRINT_NUM_UNS
JMP  stop_program

print_signed_unsigned:
CALL print
DB 0dh, 0ah, "unsigned decimal: ", 0
; print out unsigned: 
MOV  AX, SUM
CALL PRINT_NUM_UNS
CALL print
DB 0dh, 0ah, "signed decimal: ", 0
; print out singed: 
MOV  AX, SUM
CBW  ; convert byte into word. 
CALL PRINT_NUM
JMP  stop_program


error_not_valid:
CALL print
DB 0dh, 0ah, "error: only zeros and ones are allowed!", 0

stop_program:

; wait for any key.... 
CALL print
DB 0dh, 0ah, "press any key...", 0
MOV AH, 0
INT 16h
RET





; copied from c:\emu8086\emu8086.inc 
GET_STRING      PROC    NEAR
PUSH    AX
PUSH    CX
PUSH    DI
PUSH    DX

MOV     CX, 0                   ; char counter. 

CMP     DX, 1                   ; buffer too small? 
JBE     empty_buffer            ; 

DEC     DX                      ; reserve space for last zero. 


;============================ 
; loop to get and processes key presses: 

wait_for_key:

MOV     AH, 0                   ; get pressed key. 
INT     16h

CMP     AL, 13                  ; 'RETURN' pressed? 
JZ      exit


CMP     AL, 8                   ; 'BACKSPACE' pressed? 
JNE     add_to_buffer
JCXZ    wait_for_key            ; nothing to remove! 
DEC     CX
DEC     DI
PUTC    8                       ; backspace. 
PUTC    ' '                     ; clear position. 
PUTC    8                       ; backspace again. 
JMP     wait_for_key

add_to_buffer:

        CMP     CX, DX          ; buffer is full? 
        JAE     wait_for_key    ; if so wait for 'BACKSPACE' or 'RETURN'... 

        MOV     [DI], AL
        INC     DI
        INC     CX

        ; print the key: 
        MOV     AH, 0Eh
        INT     10h

JMP     wait_for_key
;============================ 

exit:

; terminate by null: 
MOV     [DI], 0

empty_buffer:

POP     DX
POP     DI
POP     CX
POP     AX
RET
GET_STRING      ENDP




; copied from c:\emu8086\emu8086.inc 
PRINT_NUM       PROC    NEAR
        PUSH    DX
        PUSH    AX

        CMP     AX, 0
        JNZ     not_zero

        PUTC    '0'
        JMP     printed_pn

not_zero:
        ; the check SIGN of AX, 
        ; make absolute if it's negative: 
        CMP     AX, 0
        JNS     positive
        NEG     AX

        PUTC    '-'

positive:
        CALL    PRINT_NUM_UNS
printed_pn:
        POP     AX
        POP     DX
        RET
ENDP



; copied from c:\emu8086\emu8086.inc 
PRINT_NUM_UNS   PROC    NEAR
        PUSH    AX
        PUSH    BX
        PUSH    CX
        PUSH    DX

        ; flag to prevent printing zeros before number: 
        MOV     CX, 1

        ; (result of "/ 10000" is always less or equal to 9). 
        MOV     BX, 10000       ; 2710h - divider. 

        ; AX is zero? 
        CMP     AX, 0
        JZ      print_zero

begin_print:

        ; check divider (if zero go to end_print): 
        CMP     BX,0
        JZ      end_print

        ; avoid printing zeros before number: 
        CMP     CX, 0
        JE      calc
        ; if AX<BX then result of DIV will be zero: 
        CMP     AX, BX
        JB      skip
calc:
        MOV     CX, 0   ; set flag. 

        MOV     DX, 0
        DIV     BX      ; AX = DX:AX / BX   (DX=remainder). 

        ; print last digit 
        ; AH is always ZERO, so it's ignored 
        ADD     AL, 30h    ; convert to ASCII code. 
        PUTC    AL


        MOV     AX, DX  ; get remainder from last div. 

skip:
        ; calculate BX=BX/10 
        PUSH    AX
        MOV     DX, 0
        MOV     AX, BX
        DIV     CS:ten  ; AX = DX:AX / 10   (DX=remainder). 
        MOV     BX, AX
        POP     AX

        JMP     begin_print

print_zero:
        PUTC    '0'

end_print:

        POP     DX
        POP     CX
        POP     BX
        POP     AX
        RET
ten             DW      10      ; used as divider.       
ENDP


; print text that follows the caller 
print PROC
MOV     CS:temp1, SI  ; store SI register. 
POP     SI            ; get return address (IP). 
PUSH    AX            ; store AX register. 
next_char:
        MOV     AL, CS:[SI]
        INC     SI            ; next byte. 
        CMP     AL, 0
        JZ      printed_ok
        MOV     AH, 0Eh       ; teletype function. 
        INT     10h
        JMP     next_char     ; loop. 
printed_ok:
POP     AX            ; re-store AX register. 
; SI should point to next command after 
; the CALL instruction and string definition: 
PUSH    SI            ; save new return address into the Stack. 
MOV     SI, CS:temp1  ; re-store SI register. 
RET
temp1  DW  ?    ; variable to store original value of SI register. 
ENDP