; Description:
;	atan2の整数(256度系)版
;
; Function
;	int pascal iatan2( int y, int x ) ;
;
; Author:
;	恋塚昭彦
;
; History:
;	92/ 7/29 Initial
;	93/ 5/29 [M0.18] .CONST->.DATA
;

MRETURN macro
	pop	BP
	ret	4
	EVEN
	endm

; int iatan2( int y, int x ) ;
func IATAN2
	push	BP
	mov	BP,SP

	; 引数
	@@y = (RETSIZE+2)*2
	@@x = (RETSIZE+1)*2

	mov	CX,[BP+@@y]
	mov	BP,[BP+@@x]

	mov	AX,CX
	or	AX,BP
	jz	short @@RETURN

	mov	AX,CX
	cwd
	xor	AX,DX
	sub	AX,DX
	mov	BX,AX			; BX = abs(y)

	mov	AX,BP
	cwd
	xor	AX,DX
	sub	AX,DX
	mov	DX,AX			; DX = abs(x)

	cmp	DX,BX			; abs(x) <= abs(y) -> jump
	je	short @@L100
	jl	short @@L150

	mov	AX,BX
	mov	BX,DX
	xor	DH,DH
	mov	DL,AH
	mov	AH,AL
	mov	AL,DH
	div	BX
	mov	BX,offset AtanTable8
	xlatb
	jmp	short @@L200
	EVEN

@@L100:	mov	AL,32
	jmp	short @@L200
	EVEN

@@L150:	mov	AX,DX
	xor	DH,DH
	mov	DL,AH
	mov	AH,AL
	mov	AL,DH
	div	BX
	mov	BX,offset AtanTable8
	xlatb
	neg	AL
	add	AL,64
@@L200:
	xor	AH,AH

	or	BP,BP
	jge	short @@L300
	neg	AX
	add	AX,128
@@L300:
	or	CX,CX
	jge	short @@L400
	neg	AL		; ax = 256 - axだけど…省略
@@L400:
	xor	AH,AH
@@RETURN:
	MRETURN
endfunc