;used for matrix inverses
invmacro MACRO	col1,col2,row1,row2
	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	cx,bx,1
	ENDM

;entry: es:di=matrix1
; exit: es:di=matrix1 (overwritten by it's inverse)
invmatrix PROC NEAR
	int 3

	invmacro 1,2,1,2
	push	cx ;(0,0)
	mov	ax,es:[di+0*2+0*6]
	imul	cx
	shld	dx,ax,1
	mov	si,dx
	invmacro 2,0,1,2
	neg	cx
	push	cx ;(1,0)
	mov	ax,es:[di+1*2+0*6]
	imul	cx
	shld	dx,ax,1
	add	si,dx
	invmacro 0,1,1,2
	push	cx ;(2,0)
	mov	ax,es:[di+2*2+0*6]
	imul	cx
	shld	dx,ax,1
	add	si,dx
	;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	cx
	push	cx ;(0,0)
	invmacro 2,0,0,2
	push	cx ;(1,0)
	invmacro 0,1,0,2
	neg	cx
	push	cx ;(2,0)
	
	invmacro 1,2,0,1
	push	cx ;(0,0)
	invmacro 2,0,0,1
	neg	cx
	push	cx ;(1,0)
	invmacro 0,1,0,1
	push	cx ;(2,0)
	
	
	pop	dx
	xor	ax,ax
	sar	dx,1
	rcr	ax,1
	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
	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
	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
	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
	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
	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
	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
	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
	sar	dx,1
	rcr	ax,1
	idiv	si
	mov	es:[di+2*2+2*6],ax
	
	ret
invmatrix ENDP

IFDEF notdef
;北北北北 _calc_invrmatrix(rmatrix *dest) 北北北北
;entry: dest=destination matrix (matrix modified)
; exit:	(data written to dest matrix)
;descr: dest=dest^-1.
_calc_invrmatrix PROC FAR
	CBEG
	lespar	di,0
	call	invmatrix
	CEND
_calc_invrmatrix ENDP
ENDIF