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@kthompson
Forked from jsutlovic/print_hex.asm
Last active August 15, 2022 15:52
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Assembly print hex
[org 0x7c00]
mov dx, 0x1fb7 ; Set the value we want to print to dx
call print_hex ; Print the hex value
jmp $ ; Hang once we're done
%include "print_string.asm"
; Prints the value of DX as hex.
print_hex:
pusha ; save the register values to the stack for later
mov cx,4 ; Start the counter: we want to print 4 characters
; 4 bits per char, so we're printing a total of 16 bits
char_loop:
dec cx ; Decrement the counter
mov ax,dx ; copy bx into ax so we can mask it for the last chars
shr dx,4 ; shift bx 4 bits to the right
and ax,0xf ; mask ah to get the last 4 bits
mov bx, HEX_OUT ; set bx to the memory address of our string
add bx, 2 ; skip the '0x'
add bx, cx ; add the current counter to the address
cmp ax,0xa ; Check to see if it's a letter or number
jl set_letter ; If it's a number, go straight to setting the value
add al, 0x27 ; If it's a letter, add 0x27, and plus 0x30 down below
; ASCII letters start 0x61 for "a" characters after
; decimal numbers. We need to cover that distance.
jl set_letter
set_letter:
add al, 0x30 ; For and ASCII number, add 0x30
mov byte [bx],al ; Add the value of the byte to the char at bx
cmp cx,0 ; check the counter, compare with 0
je print_hex_done ; if the counter is 0, finish
jmp char_loop ; otherwise, loop again
print_hex_done:
mov bx, HEX_OUT ; print the string pointed to by bx
call print_string
popa ; pop the initial register values back from the stack
ret ; return the function
HEX_OUT: db '0x0000', 0
; Padding and magic number
times 510-($-$$) db 0
dw 0xaa55
print_string: ; Push registers onto the stack
pusha
string_loop:
mov al, [bx] ; Set al to the value at bx
cmp al, 0 ; Compare the value in al to 0 (check for null terminator)
jne print_char ; If it's not null, print the character at al
; Otherwise the string is done, and the function is ending
popa ; Pop all the registers back onto the stack
ret ; return execution to where we were
print_char:
mov ah, 0x0e ; Linefeed printing
int 0x10 ; Print character
add bx, 1 ; Shift bx to the next character
jmp string_loop ; go back to the beginning of our loop
@KowalczykBartek
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Thank you very much ! thanks to that gist I was able to complete exercise 3.4.8

@s0h1s2
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s0h1s2 commented Jun 29, 2022

Thanks buddy it's an amazing thing when you see those bits and bytes.

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