cpu 8086
org 0x3000

mov bx, si

rotloop:
	cmp byte [bx], 0
	jz .end

	cmp byte [bx], 'A'
	jl .next
	cmp byte [bx], 'M'
	jle .inc
	cmp byte [bx], 'Z'
	jle .dec

	cmp byte [bx], 'a'
	jl .next
	cmp byte [bx], 'm'
	jle .inc
	cmp byte [bx], 'z'
	jle .dec

	.next:
		inc bx
		jmp short rotloop

	.inc:
		add byte [bx], 13
		jmp short .next
	.dec:
		sub byte [bx], 13
		jmp short .next
	.end:

mov ah, 2
int 0x21
int 0x20