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        org 100h
Start:
        mov ah, 09h
        mov dx, TestStr+1
        int 21h

        mov ah, 02h
        mov dl, [Char]
        int 21h

        mov ah, 09h
        mov dx, EndStr
        int 21h

        push TestStr
        xor ax, ax
        mov al, [Char]
        push ax
        call SearchChar

        mov ah, 02h
        mov dl, al
        add dl, '0'
        int 21h

        mov ah, 08h
        int 21h


SearchChar:
.prolog:
        push bp
        mov bp, sp

.searching:
        mov di, [bp+6]
        movzx cx, byte[di]
        inc di

        mov al, [bp+4]
        repne scasb

        test cx, cx
        jz .notFound


        mov si, [bp+6]
        inc si
        sub di, si
        mov ax, di
        jmp .epilog
.notFound:
        xor ax, ax

.epilog:
        mov sp, bp
        pop bp
        ret 4

TestStr db 8, "aasdasda"
EndStr db 13, 10, '$'
Char db 'q'