2_full_adder_chained/2adder.asm at main · CodeWithCompound/2_full_adder_chained · GitHub

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section .data
    a db 0b11          ; first number (bits: a1 a0)
    b db 0b01          ; second number (bits: b1 b0)
    result db 0        ; will hold sum bits (r1 r0)
    carry db 0         ; final carry out
    newline db 10      ; line feed

section .text
    global _start

_start:
    mov al, [a]
    mov bl, [b]

    ; ----- LSB full adder -----
    mov cl, al
    and cl, 1          ; cl = a0
    mov dl, bl
    and dl, 1          ; dl = b0

    mov ch, cl         ; save a0
    xor cl, dl         ; sum0 = a0 XOR b0
    mov [result], cl

    and ch, dl         ; carry0 = a0 AND b0
    mov [carry], ch

    ; ----- MSB full adder -----
    mov cl, al
    shr cl, 1
    and cl, 1          ; cl = a1
    mov dl, bl
    shr dl, 1
    and dl, 1          ; dl = b1

    mov dh, cl         ; save a1
    xor cl, dl         ; a1 XOR b1
    mov ch, [carry]    ; previous carry
    xor cl, ch         ; sum1 = (a1 XOR b1) XOR carry

    shl cl, 1
    mov dl, [result]
    or  cl, dl
    mov [result], cl

    ; ----- Final carry -----
    mov cl, dh         ; a1
    mov dl, bl
    shr dl, 1
    and dl, 1          ; dl = b1
    mov ch, [carry]    ; previous carry

    mov al, cl
    and al, dl         ; a1 & b1
    mov bl, cl
    and bl, ch         ; a1 & prev_carry
    or  al, bl
    mov bl, dl
    and bl, ch         ; b1 & prev_carry
    or  al, bl
    mov [carry], al

    ; ----- Print result and carry -----
    mov al, [result]
    add al, '0'
    mov [result], al

    mov eax, 4         ; sys_write
    mov ebx, 1         ; stdout
    mov ecx, result
    mov edx, 1
    int 0x80

    mov eax, 4
    mov ebx, 1
    mov ecx, newline
    mov edx, 1
    int 0x80

    mov al, [carry]
    add al, '0'
    mov [carry], al

    mov eax, 4
    mov ebx, 1
    mov ecx, carry
    mov edx, 1
    int 0x80

    mov eax, 4
    mov ebx, 1
    mov ecx, newline
    mov edx, 1
    int 0x80

    ; Exit
    mov eax, 1
    xor ebx, ebx
    int 0x80