Added a basic calculator in assembly x86

asmc32.sh

@@ -4,8 +4,8 @@ compile() {
     local filename="$(basename "$1")"
     local basename="${filename%.*}"
 
-    nasm -f elf32 -g -F dwarf -o "$basename.o" "$filename"
+    nasm -f elf32 -g -F dwarf -o "$basename.o" "$filename" && \
-    ld -m elf_i386 -o "$basename" "$basename.o"
+        ld -m elf_i386 -o "$basename" "$basename.o" && \
         rm "$basename.o"
 }
 

calc.asm

@@ -0,0 +1,233 @@
+; A simple calculator program that do simple operation (+, -, *, /)
+; 
+; Author: Fabio Scotto di Santolo
+; Date:   03/07/2025
+
+global _start
+
+section .text
+_start:
+    ; Prompt for first number:
+    mov eax, 0x04               ; write syscall 
+    mov ebx, 1                  ; STDOUT file descriptor
+    mov ecx, nprompt
+    mov edx, len1
+    int 0x80                    ; trigger write syscall
+    mov eax, 0x03               ; read syscall
+    mov ebx, 0                  ; STDIN file descriptor
+    mov ecx, buffer1
+    mov edx, 32 
+    int 0x80                    ; trigger read syscall
+    mov edi, buffer1            ; save buffer address
+    mov esi, eax                ; save length 
+
+    ; Prompt for second number:
+    mov eax, 0x04               ; write syscall 
+    mov ebx, 1                  ; STDOUT file descriptor
+    mov ecx, nprompt
+    mov edx, len1
+    int 0x80                    ; trigger write syscall
+    mov eax, 0x03               ; read syscall
+    mov ebx, 0                  ; STDIN file descriptor
+    mov ecx, buffer2
+    mov edx, 32 
+    int 0x80                    ; trigger read syscall
+
+    ; Convert second number
+    mov ecx, buffer2            ; save buffer address
+    mov ebx, eax                ; save length
+    call ascii_to_int
+    push eax                    ; save converted second number in the stack
+
+    ; Convert first number
+    mov ecx, edi                ; ECX = address
+    mov ebx, esi                ; EBX = length
+    call ascii_to_int           ; EAX = first number
+    push eax                    ; save converted first number in the stack
+
+    ; Prompt for operand:
+    mov eax, 0x04               ; write syscall 
+    mov ebx, 1                  ; STDOUT file descriptor
+    mov ecx, oprompt
+    mov edx, len2
+    int 0x80                    ; trigger write syscall
+    mov eax, 0x03               ; read syscall
+    mov ebx, 0                  ; STDIN file descriptor
+    mov ecx, buffer3
+    mov edx, 1
+    int 0x80                    ; trigger read syscall
+
+    ; Check operand
+    mov eax, [buffer3]          ; move in EAX operand
+    cmp eax, 0x2B               ; compare with +
+    je .add
+    cmp eax, 0x2D               ; compare with -
+    je .sub
+    cmp eax, 0x2A               ; compare with *
+    je .mul
+    cmp eax, 0x2F               ; compare with /
+    je .div
+    jmp end                     ; safety jmp to end
+
+.add:
+    pop eax
+    pop ebx
+    add eax, ebx
+    jmp result
+
+.sub:
+    pop eax
+    pop ebx
+    sub eax, ebx
+    jmp result
+    
+.mul:
+    pop eax
+    pop ebx
+    imul eax, ebx
+    jmp result  
+
+.div:
+    pop eax
+    pop ebx
+    xor edx, edx
+    idiv ebx
+    jmp result
+    
+result:
+    ; Print operation result
+    mov ebx, eax
+    mov eax, msg
+    call concat_string_num      ; concat result with final message
+   
+    mov eax, 0x04               ; write syscall 
+    mov ebx, 1                  ; STDOUT file descriptor
+    int 0x80                    ; trigger syscall
+    jmp end
+
+end:
+    ; call syscall exit
+    mov eax, 0x1
+    xor ebx, ebx                ; reset register to 0
+    int 0x80                    ; trigger syscall
+
+; --- ASCII to Integer Conversion Routine ---
+ascii_to_int:
+    push ebx
+    push ecx
+    push edx
+    push esi
+
+    xor eax, eax
+    xor edx, edx
+    mov esi, ecx
+    mov ecx, ebx
+
+convert_loop:
+    cmp byte [esi], 0xA         ; newline?
+    je convert_done
+    cmp byte [esi], 0xD         ; carriage return?
+    je convert_done
+
+    mov ebx, 10
+    mul ebx                     ; EAX *= 10
+
+    movzx ebx, byte [esi]
+    sub ebx, '0'
+    add eax, ebx                ; EAX += digit
+
+    inc esi
+    loop convert_loop
+
+convert_done:
+    pop esi
+    pop edx
+    pop ecx
+    pop ebx
+    ret
+
+; ----------------------------------------------------------------
+; concat_string_num
+; Concatenates a null-terminated string in EAX with a number in EBX.
+; Result:
+;   ECX = pointer to result string (concat_buf)
+;   EDX = length of result string (excluding null terminator)
+; Clobbers:
+;   EAX, EBX, ESI, EDI, EDX, AL, ECX
+; ----------------------------------------------------------------
+concat_string_num:
+    push eax
+    push ebx
+    push esi
+    push edi
+
+    ; Copy string from [EAX] to concat_buf
+    mov esi, eax
+    mov edi, concat_buf
+.copy_str:
+    lodsb
+    stosb
+    test al, al
+    jnz .copy_str
+    dec edi                     ; go back to overwrite null terminator
+
+    ; Convert EBX (number) to ASCII in num_buf (reversed order)
+    mov eax, ebx                ; number to convert
+    mov esi, num_buf + 11       ; write from the end
+    mov byte [esi], 0           ; null terminator
+.convert_digit:
+    dec esi
+    xor edx, edx
+    mov ebx, 10
+    div ebx                     ; EAX = EAX / 10, EDX = remainder
+    add dl, '0'
+    mov [esi], dl
+    test eax, eax
+    jnz .convert_digit
+
+    ; Copy number string from [ESI] to buffer (at current EDI)
+    mov ecx, num_buf + 12
+    sub ecx, esi                ; ECX = number string length
+    rep movsb
+    
+    ; Add newline at end
+    mov byte [edi], 0xA
+    inc edi
+
+    ; Null terminator
+    mov byte [edi], 0
+
+    ; Output: ECX = buffer, EDX = length
+    mov ecx, concat_buf
+    mov edi, concat_buf
+    xor edx, edx
+.calc_len:
+    cmp byte [edi + edx], 0
+    je .done
+    inc edx
+    jmp .calc_len
+
+.done:
+    pop edi
+    pop esi
+    pop ebx
+    pop eax
+    ret
+
+section .data
+    nprompt: db "insert a number: "
+    len1: equ $ - nprompt
+
+    oprompt: db "insert a operand (+, -, * or /): "
+    len2: equ $ - oprompt
+
+    msg: db "Result is ", 0
+    msglen: equ $ - msg
+
+section .bss
+    buffer1: resb 32
+    buffer2: resb 32
+    buffer3: resb 1
+    concat_buf: resb 256
+    num_buf: resb 12
+