Dec to Bin 2

[TipGiver]

Hello,

I want some help on converting a signed dec to bin.
I'll use the div and not the idiv. The registers for the div are:
AH AL / 2 . After this the mod is in the AH and AL has either 0 or 1

How can I know that the entered dec by the keyboard (using the INT 21H, AH=07H) is positive or negative? Let's say that i'll enter a 2-digit dec so min values is -99 and max +99. The problem is that i want to get the number; the user can enter e.g +60 or 60 which are the same.


Thank you in advance for any tip, or any other way to do this

 

[TipGiver]

I could use a little of your help at this.

I want to accept only 0 to 9. It is not working.


MOV AH,01H ;read with echo

NOTNUM: INT 21H ;read it
CMP AL,"0" ;do <ascii> - 30h
JB NOTNUM ;jump if below

CMP AL,"9" ;do <ascii> - 39h
JA NOTNUM ;jump if above


I use the Carry flag (ja and jb) but they both do not work.
Any ideas?

 

[earthandfire]

I've just type the following into debug and it woked ok (or at least seemed to)

C:\>debug
-a
0C96:0100 mov   ah, 1
0C96:0102 int   21
0C96:0104 cmp   al, 30
0C96:0106 jb    102
0C96:0108 cmp   al, 39
0C96:010A ja    102
0C96:010C mov   cl, al
0C96:010E mov   ah, 2
0C96:0110 mov   dl, 0d
0C96:0112 int   21
0C96:0114 mov   dl, 0a
0C96:0116 int   21
0C96:0118 mov   dl, cl
0C96:011A int   21
0C96:011C int   20
0C96:011E
-g
gbsgbshsh2
2
Program terminated normally
-

Hope this helps.

 

[TipGiver]

The program runs without errors, but with the two CMP i wanted to allow typing only numbers. I figured out that it will not work good if i enter ascii from 80h to ffh. These are negative, and there will be problem with the flags after the CMP.

Do you suggest an other way to accept only numbers?

 

[earthandfire]

I think you are confusing the ASCII representation of numbers and the numbers themselves.

cmp al, 30h

compares the ASCII character for 0 not 0 itself.

If you look at my earlier code you will see how I handled negative numbers.

Hope this helps.

 

[TipGiver]

Here is my working attempt. E&F requested for a little non-laughing; I'd request much more!
Here it is for anyone interested.

;Convert a 2-digit Dec number to Bin

.MODEL SMALL
.STACK
.DATA      
  table     DB ?
  msg1      DB "Enter a 2-digit decimal:",13,10,"$"
  msg2      DB 13,10,"Binary (signed):",13,10,"$"
.CODE
.STARTUP
   
MOV AX, @DATA     ; Define the DATA segment
MOV DS,AX         ;
          
MOV DH,"?"        ; Sign is undefined

;;; MESSAGE ;
MOV DX,OFFSET msg1
MOV AH,09H
INT 21H
; MESSAGE ;;;
  
REREADSIGN:     CALL READSIGN
                CALL READNUMBER
STORE1ST:       MOV table[0],AL  ; Treated as tenths   
                CALL READNUMBER     
                MOV table[1],AL  ; Treated as units

MOV BL,0

SHL table[0],1       ; Our number should be... 
ADD BL,table[0]      ; 10 * tenths + 1 * units...
SHL table[0],2       ; but it is binary, or pseudo-decimal
ADD BL,table[0]      ;
ADD BL,table[1]      ;

CMP DH,"-"           ; Check the sign of the...
JE NEGATIVE          ; inputed number
JMP POSITIVE         ;
NEGATIVE:   NEG BL   ;
POSITIVE:            ;

;;; MESSAGE ;
MOV DX,OFFSET msg2
MOV AH,09H
INT 21H
; MESSAGE ;;;

CALL SHOWBINARY

.EXIT 0


          
          
          

READNUMBER PROC NEAR
    ; READ A NUMBER. OUTPUT=AL

    NOTNUM:     CMP DH,"?"
                JE REREADSIGN
                MOV AH,07H
                INT 21H
                AND AL,7FH   ; 0111.1111B -> Remove the sign...
                CMP AL,30H   ; else trouble with flags at CMP...
    JC          NOTNUM       ; negative numbers after 80h     
                CMP AL,39H
    JNC         NOTNUM         
                CALL DISPLAYCHAR
                SUB AL,30H
    RET
READNUMBER ENDP

      
               
SHOWBINARY PROC NEAR
    ; PRINT 1 AND 0 DIGITS. INPUT=BL
    
    MOV AH,02H    ; Function to show the ascii of DL
    MOV CX,08H    ; Loop 8 times (8-bits).

    NEXT:       RCL BL,1    ; Rotate left through Carry Flag
                JNC ISZERO
        
                MOV DL,"1"
                JMP DISP
    ISZERO:     MOV DL,"0"
    DISP:       INT 21H     ; Show it
        
    LOOP        NEXT
    
    RET
SHOWBINARY ENDP
           
           

DISPLAYCHAR PROC NEAR
    ;DISPLAY THE CHAR THAT IS IN DL
    
    MOV AH,02H                 
    MOV DL,AL
    INT 21H 
    
    RET
DISPLAYCHAR ENDP



READSIGN PROC NEAR
    ; SET THE SIGN TO DH
    
    MOV AH,07H                 
    INT 21H
  
    CMP AL,"+"
    JE          SETSIGN
    CMP AL,"-"
    JE          SETSIGN
    
    ; Is number? If yes -> positive
    AND AL,7FH   
    CMP AL,30H   
    JC          ITISNOT          
    CMP AL,39H
    JNC         ITISNOT
    
    MOV DH,"+"               ; Update the sign
    CALL        DISPLAYCHAR
    SUB AL,30H
    JMP         STORE1ST     ; Store it     
    
    SETSIGN:    MOV DH,AL
                CALL DISPLAYCHAR
    RET
    ITISNOT:    JMP REREADSIGN     
READSIGN ENDP

 

[zeitghost]

You've got the "END" directive missing.

My ancient copy of TASM doesn't like the .EXIT macro.

It also whinges about "SHL table[0],2", will only take 1 as the parameter. (This might be processor related: 8088 vs anything later).

 

[TipGiver]

I do not use the END. Instead i use the .Exit which is equivalent to:
mov ax,4c00h
int 21h

The SHL gets a number and the times to perform the shift process.
This code runs at least for 80x86

 

[zeitghost]

Well TASM whinges about END being missing.

It's a directive not a macro.

.EXIT generates code (apparently, except not for me...).

END tells the assembler it's reached the end of the file...

Things may be different these days, but most of the assemblers I use throw a wobbly if END is missing.