Initial commit

nasm.asm

@@ -0,0 +1,204 @@
+; demo data for (2c – d/3) / (b – a/4):
+
+; 1. a = 12, b = 7, c = 7, d = 18
+; (2 * 7 - 18 / 3) / (7 - 12 / 4) = (14 - 6) / (7 - 3) = 8 / 4 = 2
+
+; 2. a = 180, b = 50, c = 100, d = 30
+; (2 * 100 - 30 / 3) / (50 - 180 / 4) = (200 - 10) / (50 - 45) = 190 / 5 = 38
+
+; 3. a = 10, b = 6, c = 2, d = 11
+; (2 * 2 - 11 / 3) / (6 - 10 / 4) = (4 - 3) / (6 - 2) = 1 / 4 = 0
+    
+section .data
+    GREETING: db '(2c – d / 3) / (b – a / 4)', 10
+    GREETING_LEN: equ $-GREETING 
+    LIM: db 'Limitations: 6c >= d, 4b >= a, b - a / 4 != 0, division is integer, all variables are integers', 10
+    LIM_LEN: equ $-LIM
+    ENTER_A: db 'Enter a (0 <= a <= 255): '
+    ENTER_B: db 'Enter b (0 <= b <= 255): '
+    ENTER_C: db 'Enter c (0 <= c <= 255): '
+    ENTER_D: db 'Enter d (0 <= d <= 255): '
+    RES_STR: db '(2c – d/3) / (b – a/4) = '
+    RES_STR_LEN: equ $-RES_STR
+    NEWLINE: db 10
+section .bss
+    num_buf: resb 4
+    a: resb 1
+    b: resb 1
+    c: resb 1
+    d: resb 1
+    res: resb 1
+    t1: resb 1
+    t2: resb 1
+section .text
+    global _start
+    
+%macro print 2
+    mov ecx, %1
+    mov edx, %2
+    mov eax, 4
+    mov ebx, 1
+    int 80h
+%endmacro
+
+%macro print_int 1
+; prints integer without leading 0
+; arg is a memory address of an 3 char max int as a string
+    mov eax, 3
+    cmp byte [%1], 48
+    jne %%done
+    dec eax
+    cmp byte [%1 + 1], 48
+    jne %%done
+    dec eax
+
+%%done:
+    mov ebx, 3
+    sub ebx, eax
+    mov edx, %1
+    add edx, ebx
+    
+    mov ecx, edx
+    mov edx, eax
+    mov eax, 4
+    mov ebx, 1
+    int 80h
+%endmacro
+
+%macro inttostr 2
+; CONVERTING NUMBER TO STRING
+    xor eax, eax
+    mov al, [%1]
+    mov cx, 10 ; divider
+    
+    mov dx, 0
+    div cx ; divides edx:eax by arg stores result in eax and remainder in edx
+    add dx, 48
+    mov [%2 + 2], dl
+    
+    mov dx, 0
+    div cx
+    add dx, 48
+    mov [%2 + 1], dl
+    
+    mov dx, 0
+    div cx 
+    add dx, 48
+    mov [%2], dl
+%endmacro
+
+%macro readln_int 1
+    mov eax, 3
+    mov ebx, 2
+    mov ecx, num_buf
+    mov edx, 4
+    int 80h
+    
+    mov byte [num_buf + 3], 10 ; manually set end of line (user can try to input 1234)
+    
+    mov ebx, 0
+    mov edx, num_buf
+%%int_len:
+    xor eax, eax ; ~ mov eax, 0
+    mov al, byte [edx]
+    push eax
+    inc edx
+    inc ebx
+    cmp al, 10
+    jne %%int_len
+    
+    pop eax ; removing \n from the stack
+    dec ebx ; \n is not the digit
+; now ebx contains amount of digits in number and stack contains all the digits as chars
+
+    xor ecx, ecx
+    cmp ebx, 0 ; if 0 digits => done
+    je %%done
+
+    pop ecx
+    sub ecx, 48 ; converting from char to int, that it represent
+    cmp ebx, 1 ; if 1 digit
+    je %%done
+    
+    pop eax
+    sub eax, 48
+    mov edx, 10
+    mul dl ; mul multiplies eax by arg and stores res in eax
+    add ecx, eax
+    cmp ebx, 2 ; if 2 digits
+    je %%done
+    
+    pop eax
+    sub eax, 48
+    mov edx, 100
+    mul dl
+    add ecx, eax
+%%done: 
+; now ecx contains the number
+
+    mov [%1], cl ; storing first byte of it to the memory
+%endmacro
+    
+_start:
+    print GREETING, GREETING_LEN
+    print LIM, LIM_LEN
+    
+    print ENTER_A, 25
+    readln_int a
+    
+    print ENTER_B, 25
+    readln_int b
+    
+    print ENTER_C, 25
+    readln_int c
+    
+    print ENTER_D, 25
+    readln_int d
+    
+    ; t1 = (2c – d/3)
+    xor eax, eax
+    mov al, [c]
+    mov ecx, 2
+    mul cx
+    mov [t1], al
+    
+    xor eax, eax
+    mov al, [d]
+    mov ecx, 3
+    div cx
+    mov [t2], al
+    
+    xor eax, eax
+    xor ebx, ebx
+    mov al, [t1]
+    mov bl, [t2]
+    sub eax, ebx
+    mov [t1], al
+    
+    ; t2 = (b – a/4)
+    xor eax, eax
+    mov al, [a]
+    mov ecx, 4
+    div cx
+    xor ebx, ebx
+    mov bl, [b]
+    sub ebx, eax
+    mov [t2], bl
+    
+    ; res = (t1 / t2) = (2c – d/3) / (b – a/4)
+    xor eax, eax
+    xor ecx, ecx
+    xor edx, edx
+    mov al, [t1]
+    mov cl, [t2]
+    div cx
+    mov [res], al
+    
+    print RES_STR, RES_STR_LEN
+    inttostr res, num_buf
+    print_int num_buf
+    print NEWLINE, 1
+    
+    mov eax, 1
+    mov ebx, 0
+    int 80h