checkhiddenbx PROC NEAR
	push	si
	mov	ax,es:[bx]
	mov	si,es:[bx+2]
	sub	ax,es:[bx+4]
	sub	si,es:[bx+8+2]
	imul	si
	push	ax
	push	dx
	mov	ax,es:[bx+2]
	mov	si,es:[bx]
	sub	ax,es:[bx+4+2]
	sub	si,es:[bx+8]
	imul	si
	pop	cx
	pop	si
	sub	ax,si
	sbb	dx,cx
	pop	si
	cmp	dx,0
	jl	@@1
	clc
	ret
@@1:	stc
	ret
checkhiddenbx ENDP