; This simple program takes 10 integers from the user and
; counts how many of these integers are odd
;
; Source: http://courses.ics.hawaii.edu/ReviewICS312/modules/subprograms/
;

%include "asm_io.inc"

segment .data
    msg_odd    db    "The number of odd numbers is: ",0

segment .bss
    integers resd    10     ; space to store 10 32-bit integers

segment .text
    global    asm_main
asm_main:
    enter   0,0             ; set up
    pusha                   ; set up

    push    integers        ; we pass integers to get_integers
    push    dword 10        ; we pass the number of integers to get_integers 
    call    get_integers    ; call get_integers
    add     esp, 8          ; clean up the stack (often done as op ecx twice, which may be quicker)
    mov     eax, msg_odd    ; store the address of the message to print into eax
    call    print_string    ; print the message
    push    integers        ; we pass integers to count_odds    
    push    10              ; we pass the number of integers to count_odds
    call    count_odds      ; call count_odds
    add     esp, 8          ; clean up the stack
    call    print_int       ; print the content of eax as an integer (this is what count_odds returned)
    call    print_nl        ; print a new line

    popa                    ; clean up
    mov     eax, 0          ; clean up
    leave                   ; clean up
    ret                     ; clean up

;   FUNCTION: Get_Integers
;   Takes two parameters:  an address in memory in which to store integers, and a number of integers to store (>0)
;   Destroys values of eax, ebx, and ecx!!

segment .data
    msg_int        db    "Enter an integer: ",0

segment .text
get_integers:
    push    ebp             ; save the value of EBP of the caller
    mov     ebp, esp        ; update the value of EBP for this subprogram

    mov     ecx, [ebp + 12] ; ECX = address at which to store the integers (parameter #1)
    mov     ebx, [ebp + 8]  ; EBX = number of integers to read (parameter #2)
    shl     ebx, 2          ; EBX = EBX * 4  (unsigned)
    add     ebx, ecx        ; EBX = ECX + EBX = address beyond that of the last integer to be stored
loop1:
    mov     eax, msg_int    ; EAX = address of the message to print
    call    print_string;   ; print the message
    call    read_int        ; read an integer from the keyboard (which will be stored in EAX)
    mov     [ecx], eax      ; store the integer in memory at the correct address
    add     ecx, 4          ; ECX = ECX + 4 
    cmp     ecx, ebx        ; compare ECX, EBX
    jb      loop1           ; if ECX < EBX, jump to loop1   (unsigned)

    pop     ebp             ; restore the value of EBP
    ret                     ; clean up

;   FUNCTION: count_odds
;   Takes two parameters:  an address in memory in which integers are stored, and the number of integers (>0)
;   Destroys values of eax, ebx, and edx!!  (eax = returned value)

segment .text
count_odds:
    push    ebp             ; save the value of EBP of the caller
    mov     ebp, esp        ; update the value of EBP for this subprogram

    mov     eax, [ebp + 12] ; ECX = address at which integers are stored (parameter #1)
    mov     ebx, [ebp + 8]  ; EBX = number of integers (parameter #2)
    shl     ebx, 2          ; EBX = EBX * 4  (unsigned)
    add     ebx, eax        ; EBX = ECX + EBX = address beyond that of the last integer
    sub     ebx, 4          ; EBX = EBX - 4 = address of the last integer
    xor     edx, edx        ; EDX = 0
loop2:

    push    dword [ebx]     ; store the current integer on the stack
    call    is_odd          ; call is_odd  
    add     esp, 4          ; clean up the stack
    add     edx, eax        ; EDX += EAX  (EAX = 0 if even, EAX = 1 if odd)
    sub     ebx, 4          ; ECX = ECX - 4 
    cmp     ebx, [ebp+12]   ; compare EBX and the address of the first integer
    jnb     loop2           ; if EBX >= [EBP+12]  jump to loop2   (unsigned)
    
    mov     eax, edx        ; EAX = EDX (= number of odd integers)
    
    pop     ebp             ; restore the value of EBP
    ret                     ; clean up


;   FUNCTION: is_odd
;   Takes one parameter:  an integers (>0)
;   Destroys values of eax and ecx (eax = returned value)

segment .text
is_odd:
    push    ebp             ; save the value of EBP of the caller
    mov     ebp, esp        ; update the value of EBP for this subprogram

    mov     eax, 0          ; EAX = 0
    mov     ecx, [ebp+8]    ; EBX = integer (parameter #1)
    shr     ecx, 1          ; Right logical shift
    adc     eax, 0          ; EAX = EAX + carry  (if even: EAX = 0, if odd: EAX = 1)
    
    pop     ebp             ; restore the value of EBP
    ret                     ; clean up