Adding two numbers in base 10 on Assembler

Question

How can I add 2 numbers that their value is on base 16 and make the result on "base 10" on assembler. For example:

"5h+5h=10h" - I know it's wrong, I just want it to be visually 10h

And not:

5h+5h=Ah

CODE:

MOV AX,5h
MOV BX,5h
ADD AX,BX

result: ax=Ah - Not the result that i want...

result: ax=10h - The result that i want.

I tried to figure it out with google but didn't find anything that can help me...

Check out the DAA instruction http://x86.renejeschke.de/html/file_module_x86_id_69.html — BitBank, Mar 04 '15 at 10:59
Sounds like you're talking about BCD (binary coded decimal) Arithmetic. You may find [this answer](http://stackoverflow.com/questions/2359527/assembler-why-bcd-exists) useful. — Component 10, Mar 04 '15 at 10:59
The addition operation is base-agnostic. This is a matter of representation, i.e. how to convert a string from/to a number — Niklas B., Mar 04 '15 at 11:09
What's the point? How would 5h+5h yield 10h? If that's some magic arithmetic you'll have to craft it yourself? — sharptooth, Mar 04 '15 at 11:26
Can you please give me a link for Assembler code that do that practicly? — BananaBuisness, Mar 04 '15 at 11:26
Look i did " "5h+5h=10h" " that mean that I just want it visualy do 10h and not 0Ah — BananaBuisness, Mar 04 '15 at 11:31
the question really is do you want `BCD` or `hex to dec` conversion? what is the range of input operands? what about sign? the output should be hex number which is printed the same as decadic result would be (and the input values also ...)? how many digits ? no decimals I hope .... — Spektre, Mar 04 '15 at 11:50
Well I'm building a calculator and it take number with max length of 5 chars in num... — BananaBuisness, Mar 04 '15 at 19:19

score 4 · Answer 1 · answered Mar 04 '15 at 11:53

4

Here is the code you are looking for

MOV AX,5h
MOV BX,5h
ADD AX,BX
DAA

Now AX contains 10h

answered Mar 04 '15 at 11:53

Fifoernik

9,779
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Can you explain what DAA does? – BananaBuisness Mar 04 '15 at 19:15
There is a problem if u do MOV ax,999h MOV bx,1h ADD AX,BX DAA its return: 900h and not 1000h – BananaBuisness Mar 04 '15 at 19:54
1

`DAA` corrects the result of an addition of 2 packed BCD's. The first pair of packed BCD has to be in the AL register. – Fifoernik Mar 05 '15 at 11:55

BananaBuisness · Accepted Answer · 2015-03-05T11:57:17.313

Ok so i figure it out with @Fifoernik 's help so the problem is that if i want to do it with 16bit (for example 99h+1h) values i need to do it like this using DAA operan and CF flag

    pop ax
    pop bx
    add al,bl
    daa ; dec id values
    mov cl,al
    mov al,ah
    jc Carry; do i have carry 
    add al,bh
    daa ; do the magic thing
    JMP finito
    Carry:
    add al,1 ; add the carring...
    add al,bh
    daa ;can some one tell me what exactly daa does?
    finito:
    mov ch,al
    push cx
    ret

daa working only on AL so you'ill need to use the carry flag to add the carry like:

AH AL
 1 <----- carry
00 99 <-- DAA take care of the 99 and make it 0 when its A0h
00 01+
-- --
01 00 ---> result 100h

Please note that the `ret` at the tenth line should be replaced with a `jmp` towards the 3 last lines! Now you do not always return the desired result in CX and on the stack. — Fifoernik, Mar 05 '15 at 11:50

Adding two numbers in base 10 on Assembler

2 Answers2