Printing out a number in assembly language?

Question

mov al,10
add al,15

How do I print the value of \'al\'?

Answer 1

Assuming you are writing a bootloader or other application that has access to the BIOS, here is a rough sketch of what you can do:

• Isolate the first digit of the hex byte
• If it is greater than 9 (i.e. 0x0A to 0x0F), subtract 10 from it (scaling it down to 0 to 5), and add 'A' (0x41).
• If it is less than or equal to 9 (i.e. 0x00 to 0x09), add '0' to it.
• Repeat this with the next hex digit.

Here is my implementation of this:

; Prints AL in hex.
printhexb:
    push ax
    shr al, 0x04
    call print_nibble
    pop ax
    and al, 0x0F
    call print_nibble
    ret
print_nibble:
    cmp al, 0x09
    jg .letter
    add al, 0x30
    mov ah, 0x0E
    int 0x10
    ret
.letter:
    add al, 0x37
    mov ah, 0x0E
    int 0x10
    ret