A case inverter in 16-bit DOS assembly

This is a simple case inverter, if you want to try this out download the a86 assembler here. It works like a charm in dosemu-freedos.

; case inverter
	
start:
        mov ah, 0ah
        lea dx, strptr
        int 21h
	
        lea si, string
        mov cl, [strlen]
	
check:
        mov al, [si]
        cmp al, 'Z'
        ja lowercase
        cmp al, 'a'
        jb uppercase
	
lowercase:
        cmp al, 'a'
        jb traverse
        cmp al, 'z'
        jbe toupper
	
uppercase:
        cmp al, 'Z'
        ja traverse
        cmp al, 'A'
        jae tolower
	
toupper:
        sub al, 32
        mov [si], al
        jmp traverse
	
tolower:
        add al, 32
        mov [si], al
	
traverse:
        inc si
	
loop check
	
        mov ah, 02h
        mov dl, 10
        int 21h
	
        mov ah, 09h
        lea dx, string
        int 21h
        int 20h
	
strptr  label byte
maxlen  db 49
strlen  db ?
string  db 50 dup ('$')

“Fortune favors the prepared mind.” - Louis Pasteur