;used for matrix inverses
invmacro MACRO	row1,row2,col1,col2
	mov	ax,es:[di+col1+row1*6]
	imul	word ptr es:[di+col2*2+row2*6]
	mov	cx,dx
	mov	bx,ax
	mov	ax,es:[di+col1*2+row2*6]
	imul	word ptr es:[di+col2*2+row1*6]
	sub	cx,dx
	sbb	bx,ax
	shld	ecx,bx,1+16
	ENDM

;entry: es:di=matrix1
; exit: es:di=matrix1 (overwritten by it's inverse)
invmatrix PROC NEAR
	invmacro 1,2,1,2
	push	ecx ;(0,0)
	movsx	eax,es:[di+0*2+0*6]
	imul	ecx
	mov	esi,eax
	invmacro 2,0,1,2
	neg	ecx
	push	ecx ;(1,0)
	movsx	eax,es:[di+1*2+0*6]
	imul	ecx
	add	esi,eax
	invmacro 0,1,1,2
	push	ecx ;(2,0)
	movsx	eax,es:[di+2*2+0*6]
	imul	ecx
	add	esi,edx
	;si=determinant
	
	or	si,si
	jnz	@@1
	pop	cx
	pop	cx
	pop	cx
	ret	;matrix can not be inversed
@@1:
	invmacro 1,2,0,2
	neg	ecx
	push	ecx ;(0,0)
	invmacro 2,0,0,2
	push	ecx ;(1,0)
	invmacro 0,1,0,2
	neg	ecx
	push	ecx ;(2,0)
	
	invmacro 1,2,0,1
	push	ecx ;(0,0)
	invmacro 2,0,0,1
	neg	ecx
	push	ecx ;(1,0)
	invmacro 0,1,0,1
	push	ecx ;(2,0)
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+0*2+0*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+0*2+1*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+0*2+2*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+1*2+0*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+1*2+1*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+1*2+2*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+2*2+0*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+2*2+1*6],ax
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+2*2+2*6],ax
	
	ret
invmatrix ENDP