; master library - 
;
; Description:
;	EGCによる部分下スクロール
;
; Functions/Procedures:
;	void egc_shift_down(int x1, int y1, int x2, int y2, int dots);
;
; Parameters:
;	dots
;
; Returns:
;	none
;
; Binding Target:
;	Microsoft-C / Turbo-C / Turbo Pascal
;
; Running Target:
;	PC-9801VX
;
; Requiring Resources:
;	CPU: 186
;	EGC
;
; Notes:
;	
;
; Assembly Language Note:
;	
;
; Compiler/Assembler:
;	TASM 3.0
;	OPTASM 1.6
;
; Author:
;	Kazumi
;
; Revision History:
;$Id: dshift.asm 0.02 92/05/28 22:49:49 Kazumi Rel $
;	94/ 5/16 Initial: egcsftd.asm/master.lib 0.23
;
;
;

func EGC_SHIFT_DOWN	; egc_shift_down() {
	push	BP
	mov	BP,SP
	push	DS
	push	SI
	push	DI

	x1	= (RETSIZE+5)*2
	y1	= (RETSIZE+4)*2
	x2	= (RETSIZE+3)*2
	y2	= (RETSIZE+2)*2
	dots	= (RETSIZE+1)*2

	mov	CX,[BP+x1]
	mov	DX,[BP+x2]
	mov	SI,[BP+y2]
	mov	DI,[BP+dots]
	mov	AX,DI
	shl	AX,2
	add	AX,DI
	shl	AX,4			; dots * 80
	mov	WORD PTR CS:[egcsftd_diff],AX
	mov	AX,SI
	sub	AX,[BP+y1]
	mov	BX,AX
	inc	BX			; line count
	mov	AX,SI
	shl	SI,2
	add	SI,AX
	shl	SI,4			; y2 * 80
	mov	AX,DX
	shr	AX,3
	and	AX,0fffeh		; LSB = 0
	add	SI,AX			; start address
	shr	AX,1
	mov	BP,CX
	shr	BP,4
	sub	AX,BP
	inc	AX
	mov	BP,DX
	sub	BP,CX			; bit length(not inc !!)
	mov	CX,AX			; 転送 word 数
	and	DL,0fh
	mov	DH,15
	sub	DH,DL			; Src Bit Address
	mov	DL,DH
	xor	DH,DH
	mov	AX,DX			; Dest Bit Address
	push	BX
	push	BP
	mov	BX,BP
	add	BX,AX
	shr	BX,4
	add	BP,DX
	shr	BP,4
	cmp	AL,DL
	je	short @@none
	jl	short @@less
	cmp	BX,BP
	jne	short @@none
	jmp	SHORT @@plus
	EVEN
@@less:	cmp	BX,BP
	jge	short @@none
	EVEN
@@plus:	inc	CX
	EVEN
@@none:	pop	BP
	pop	BX
	shl	DL,4
	or	DL,AL
	mov	DI,DX
	mov	AX,41
	sub	AX,CX
	shl	AX,1
	mov	BYTE PTR CS:[egcsftd_sub_si],AL
	mov	BYTE PTR CS:[egcsftd_sub_di],AL
	mov	AL,00000111b		; RegWriteEnable
	out	6ah,AL
	mov	AL,80h			; CGmode = 1
	out	7ch,AL
	mov	AL,05h			; ExBit = 1
	out	6ah,AL
	mov	DX,04a0h
	mov	AX,0fff0h		; アクティブプレーン
	out	DX,AX
	mov	DX,04a2h
	mov	AX,00ffh		; FGC/BGC/リードプレーン
	out	DX,AX
	mov	DX,04a4h
	mov	AX,28f0h		; モードレジスタ/ROPコードレジスタ
	out	DX,AX
	mov	DX,04a8h
	mov	AX,0ffffh		; マスクレジスタ
	out	DX,AX
	mov	DX,04ach
	mov	AX,DI			; dir/Bitアドレス
	or	AX,1000h		; dir = 1
	out	DX,AX
	mov	DX,04aeh
	mov	AX,BP			; ビット長
	out	DX,AX
	std
	mov	AX,0a800h
	mov	DS,AX
	mov	ES,AX
	mov	DI,SI
	add	DI,1111h		; dummy
egcsftd_diff	EQU	$-2
	mov	DX,CX
	EVEN
@@next_line:	mov	CX,DX
	rep	movsw
	inc	SI
	inc	SI
	inc	DI
	inc	DI
	sub	SI,80			; dummy
egcsftd_sub_si	EQU	$-1
	sub	DI,80			; dummy
egcsftd_sub_di	EQU	$-1
	dec	BX
	jne	@@next_line
	cld
	mov	DX,04a0h
	mov	AX,0fff0h
	out	DX,AX
	mov	AL,04h			; ExBit = 0
	out	6ah,AL
	mov	AL,00h			; GRCG stop
	out	7ch,AL
	mov	AL,00000110b		; RegWriteDisable
	out	6ah,AL

	pop	DI
	pop	SI
	pop	DS
	pop	BP
	ret	5*2
endfunc		; }