Use 286 shifts and rotates

ponydos.asm

@@ -100,8 +100,7 @@ mainloop:
 	mov bx, [mouse_x]
 	shr bx, 1
 	mov cx, [mouse_y]
-	shr cx, 1
-	shr cx, 1
+	shr cx, 2
 	cmp [mouse_column], bl
 	jne .update_cursor
 	cmp [mouse_row], cl
@@ -155,8 +154,7 @@ flip_mouse_cursor:
 	; Swap foreground and background colours
 	inc bx
 	mov al, [es:bx]
-	mov cl, 4
-	ror al, cl
+	ror al, 4
 	mov [es:bx], al
 
 	popa
@@ -404,8 +402,7 @@ hexprint16:
 hexprint8:
 	push ax
 	push cx
-	mov cl, 4
-	shr al, cl
+	shr al, 4
 	call hexprint4
 	pop cx
 	pop ax