func.asm

extern printf
extern putchar

section .data
    format: dd "%d", 10, 0
    char_form: db "%c", 10, 0
    int_form: db "%d", 10, 0
    str_form: db "%s", 10, 0
    string: db "Wind On The Hills!", 20, 0

section .text
    global  IsBetweenAandB, RemCharCodeFromAToB, DebugStart, DebugEnd

;==========================================================================
; RemCharCodeFromAToB - removes all chars between a and e from str
; arguments:
;   str - string to be processed
;   a   - start
;   e   - end
; return value:
;   n/a
;--------------------------------------------------------------------------
RemCharCodeFromAToB:
    ; standard entry sequence
    push    ebp             ; save the previous value of ebp for the benefi$
    mov     ebp, esp        ; copy esp -> ebp so that ebp can be used as a $

    ; accessing arguments
                            ; [ebp + 0] = old ebp stack frame
                            ; [ebp + 4] = return address
    mov     edx, [ebp + 8]  ; string address

    while_loop_rcc:
        mov cl, [edx]       ; obtain the address of the 1st character of the string
        cmp cl, 0           ; check the null value

        je  while_loop_exit_rcc     ; exit if the null-character is reached

        mov al, cl ; save cl
        mov cl, [ebp + 16]      ; end-char
        push cx                 ; push end-char
        mov cl, [ebp + 12]      ; start-char
        push cx                 ; push start-char
        push ax;                ; push ch
        call IsBetweenAandB
        add esp, 12

        cmp eax, 0          ; if(ch is not between 'a' and 'e')

        je inner_loop_exit_rcc

        mov eax, edx    ; copy the current address

        inner_loop_rcc:
            mov cl, [eax+1]
            cmp cl, 0
            je  inner_loop_exit_rcc

            mov [eax], cl

            inc eax
            jmp inner_loop_rcc
        inner_loop_exit_rcc:

        inc edx             ; increment the address
        jmp while_loop_rcc  ; start the loop again
    while_loop_exit_rcc:

    ; standard exit sequence
    mov     esp, ebp        ; restore esp with ebp
    pop     ebp             ; remove ebp from stack
    ret                     ; return the value of temporary variable
;===================================================================

DebugStart:
    mov eax, 'x'
    call PrintChar_db
    ret

DebugEnd:
    mov eax, 'y'
    call PrintChar_db
    ret

;===================================================================
; IsBetweenAandB - tests a character if it is between 'a' and 'b'
; arguments:
;   ch = character to be tested
;   a = start character
;   b = end character
; return value:
;   1 = yes
;   0 = no
;----------------------------------------------------------------
IsBetweenAandB:
    push    ebp
    mov ebp, esp
                        ; [ebp]     = old ebp stack frame
                        ; [ebp + 4] = return address
    mov eax, [ebp + 8]  ; [ebp+8] = ch
    push ecx
    mov ecx, [ebp + 12] ; 'a' = start
    mov edx, [ebp + 16] ; 'e' = end

    cmp eax, ecx    ; compare 'ch' with 'a'
    jae next_test_ibab  ; if(ch>='a')
    jb  set_zero_ibab   ; if(ch<'a')

next_test_ibab:
    cmp eax, edx    ; compare 'ch' with 'e'
    jbe set_one_ibab        ; if(ch<='e')
    ja  set_zero_ibab   ; if(ch>'e')

set_one_ibab:
    mov eax, 1
    jmp returns_ibab

set_zero_ibab:
    mov eax, 0

returns_ibab:
    pop ecx

    mov     esp, ebp
    pop     ebp
    ret