erkyrath.infocom-zcode-terps/c-128/xzip/objects.asm

	PAGE	
	STTL "--- OBJECT & PROPERTY HANDLERS ---"


; ********************************************
; AN ASSUMPTION HAS BEEN MADE WITH EZIP OBJECT
; HANDLING. THAT IS THAT ALL THIS STUFF IS
; BEFORE PURBOT AND  IS IN MAIN MEMORY
; AND THEREFORE DIRECT ACCESSING IS JUST FINE
; LINDE
; ********************************************
; ----------------------------------
; GET ABSOLUTE ADDRESS OF OBJECT [A]
; ----------------------------------
; ENTER: OBJECT IN A/X (LO/HI)
; EXIT: ADDRESS IN [I]
; (EZIP VERSION)

OBJLOC:	STX	I+HI	; SAVE MSB FOR SHIFTING
	ASL	A	;	MULTIPLY BY LENGTH OF AN ENTRY (14)
	STA	I+LO	
	ROL	I+HI	
	LDX	I+HI	
	ASL	A		
	ROL	I+HI	; *4
	ASL	A		
	ROL	I+HI	; *8
	ASL	A		
	ROL	I+HI	; *16
	SEC		
	SBC	I+LO	; -(*2)
	STA	I+LO	; SO IS *14 TOTAL
	LDA	I+HI	
	STX	I+HI	
	SBC	I+HI	
	STA	I+HI	
	LDA	I+LO	
	CLC		
	ADC	#112	; ADD OBJECT TABLE OFFSET
	BCC	OBJ3	
	INC	I+HI	
OBJ3:
	CLC			; NEXT ADD THE ABS ADDR
	ADC	OBJTAB+LO	; OF THE OBJECT TABLE
	STA	I+LO	
	LDA	I+HI	
	ADC	OBJTAB+HI	
	STA	I+HI	
	RTS		
; -----------------------------
; GET ADDRESS OF PROPERTY TABLE
; -----------------------------
; EXIT: [I] HAS ABSOLUTE ADDR OF PROPERTY TABLE
; [Y] HAS OFFSET TO START OF PROP IDS
PROPB:	LDA	ARG1+LO	
	LDX	ARG1+HI	; (EZIP)
	JSR	OBJLOC	
	LDY	#12	; (EZIP)
	LDA	(I),Y	; GET MSB OF P-TABLE ADDRESS
	CLC		
	ADC	ZCODE	; MAKE IT ABSOLUTE
	TAX		; AND SAVE HERE
	INY		
	LDA	(I),Y	; NOW GET LSB
	STA	I+LO	
	STX	I+HI	; [I] NOW POINTS TO PROP TABLE
	LDY	#0	
	LDA	(I),Y	; GET LENGTH OF SHORT DESC
	ASL	A	;	WORD-ALIGN IT
	TAY		; EXPECTED HERE
	INY		; POINT JUST PAST THE DESCRIPTION
	RTS		


; -------------------
; FETCH A PROPERTY ID
; -------------------
; ENTRY: LIKE "PROPB" EXIT

PROPN:	LDA	(I),Y	
	AND	#%00111111	; MASK OUT LENGTH BITS (EZIP)
	RTS		


; -------------------------------
; FETCH # BYTES IN PROPERTY VALUE
; -------------------------------
; ENTRY: LIKE "PROPB" EXIT
; (EZIP)

PROPL:	LDA	(I),Y	; CHECK LENGTH FLAGS
	AND	#%10000000	; TEST BIT 7
	BEQ	SHORT	; OFF, SO 1 OR 2 BYTES
	INY		
	LDA	(I),Y	; NEXT BYTE HAS LENGTH
	AND	#%00111111	; MASK OFF EXTRA BITS
	RTS		

SHORT:	LDA	(I),Y	; PICK UP BYTE AGAIN
	AND	#%01000000	; BIT 6
	BEQ	ONE	
	LDA	#2	; BIT 6 = 1, LENGTH =2
	RTS		
ONE:	LDA	#1	; BIT 6 = 0, LENGTH =1
	RTS		


; ----------------------
; POINT TO NEXT PROPERTY
; ----------------------
; ENTRY: LIKE "PROPB" EXIT

PROPNX:	JSR	PROPL	; GET LENGTH OF CURRENT PROP
	TAX		; SAVE HERE
PPX:	INY		; LOOP UNTIL
	BNE	PPY	
	INC	I+LO	
	BNE	PPY	
	INC	I+HI	
PPY:	DEX		; [Y] POINTS TO
	BNE	PPX	; START OF NEXT PROP
	INY		; CORRECT ALIGNMENT
	RTS		


; -----------------------------------------
; CALL PROPNX, THEN ALIGN [I] AT THAT ENTRY
; -----------------------------------------
; EXIT: [I] IS ALIGNED AT CURRENT PROPERTY
; [Y] IS ZEROED
; (EZIP)

NEXTPI:	JSR	PROPNX	; GET ALIGNMENT OF NEXT PROPERTY INTO [Y]
	TYA		; ADD OFFSET TO NEXT PROP
	CLC		; TO [I] SO I POINTS DIRECTLY
	ADC	I+LO	; AT IT
	STA	I+LO	
	BCC	NXTPI1	
	INC	I+HI	; ADD IN CARRY
NXTPI1:	LDY	#0	; CLEAR [Y] AS IT IS USED AS AN INDEX
	RTS		


; ----------------
; GET OBJECT FLAGS
; ----------------
; ENTRY: OBJECT # IN [ARG1], FLAG # IN [ARG2]
; EXIT: FLAG WORD IN [K], BIT ID IN [J],
; FLAG WORD ADDRESS IN [I]

FLAGSU:	LDA	ARG1+LO	; (EZIP)
	LDX	ARG1+HI	
	JSR	OBJLOC	; GET OBJECT ADDR IN [I]
	LDA	ARG2+LO	; LOOK AT FLAG ID
	CMP	#$10	; FIRST SET OF FLAGS?
	BCC	FLS1	; YES, ADDR IN [I] IS CORRECT
	SBC	#16	; ELSE ZERO-ALIGN FLAG INDEX
	TAX		; SAVE IT HERE
	CMP	#$10	; CHECK IF IN 2ND WORD
	BCC	FLS	; YES, GO ALIGN FOR THAT
	SBC	#16	; ELSE ALIGN TO 3RD WORD
	TAX		
	LDA	I+LO	
	CLC		
	ADC	#4	; 3RD FLAG WORD
	STA	I+LO	
	BCC	FLS0	
	INC	I+HI	
	JMP	FLS0	; (END EZIP CHGS)
FLS:	LDA	I+LO	; ADD 2 TO ADDRESS IN [I]
	CLC		; TO POINT TO ADDRESS OF
	ADC	#2	; 2ND FLAG WORD
	STA	I+LO	
	BCC	FLS0	
	INC	I+HI	
FLS0:	TXA		; RESTORE INDEX
FLS1:	STA	K+LO	; SAVE FLAG ID HERE
	LDX	#1	; INIT THE
	STX	J+LO	; FLAG WORD TO
	DEX		; $0001
	STX	J+HI	
	LDA	#15	; SUBTRACT THE BIT POSITION
	SEC		; FROM 15
	SBC	K+LO	; TO GET THE SHIFT LOOP
	TAX		; INDEX
	BEQ	FLS2	; EXIT NOW IF NO SHIFT NEEDED
FLSL:	ASL	J+LO	; SHIFT THE BIT
	ROL	J+HI	; INTO POSITION
	DEX		
	BNE	FLSL	
FLS2:	LDY	#0	; MOVE THE FLAG WORD
	LDA	(I),Y	; INTO [J]
	STA	K+HI	; FIRST THE MSB
	INY		
	LDA	(I),Y	
	STA	K+LO	; THEN THE LSB
	RTS		

	END