;
;	File:		Queue.a
;
;	Contains:	Macintosh Core Utility Routines -- Enqueue, Dequeue, InitQueue
;
;	Written by:	Andy Hertzfeld  23-APR-81
;
;	Copyright:	© 1982-1993 by Apple Computer, Inc., all rights reserved.
;
;	Change History (most recent first):
;
;	   <SM3>	 9/12/93	pdw		Added EnqueueHead routine.
;	   <SM2>	 5/21/92	kc		Append "Trap" to the names of Enqueue and Dequeue to avoid name
;									conflict with the glue.
;		 <3>	 8/30/91	JSM		Cleanup header.
;		 <2>	 6/12/91	LN		Changed #include 'HardwareEqu.a' to 'HardwarePrivateEqu.a'
;	   <1.1>	11/10/88	CCH		Fixed Header.
;	   <1.0>	 11/9/88	CCH		Adding to EASE.
;	  <¥1.1>	 9/23/88	CCH		Got rid of inc.sum.d and empty nFiles
;	   <1.0>	 2/10/88	BBM		Adding file for the first time into EASEÉ
;	  <C206>	 10/9/86	bbm		Modified to mpw aincludes.
;				 2/19/86	BBM		Made some modifications to work under MPW
;				 7/24/85	RDC		Changed interrupt level settings to use equate Added spearate
;									include statement for HWequ file (no longer in systlqk.sym)
;				 1/31/85	LAK		Removed unsightly RTE's (for 68020 compatibility).
;				 1/23/85	LAK		Adapted for new equate files.
;				  8/8/83	LAK		made code-savings changes suggested in walkthru.
;				 2/23/83	LAK		changed a Move to a MoveQ, a Cmp to a Cmp.L.
;				  5/2/82	LAK		removed set and reset of queue-in-use flags since disabling
;									interrupts already guaranteed exclusion.
;

				BLANKS			ON
				STRING			ASIS


				LOAD		'StandardEqu.d'
				INCLUDE		'HardwarePrivateEqu.a'

;
;-----------------------------------------------------------------------
;
; ENQUEUE -- add a queue element to a queue.  
;	On entry, 
;		A0 points to the queue element
;		A1 points to the queue header
;
;	All registers are preserved; there are no error conditions.
;
;	The element is inserted at the end of the list.
;
;	We don't check to see if the element is already in the queue because
;	this would be slow and if the caller needs such functionality, it should
;	do it itself.
;	
;-----------------------------------------------------------------------
;
ENQUEUETRAP		PROC	EXPORT

				MOVE	SR,-(SP)				;preserve status
				ADDQ	#2,A1					;point to QHead
				ORI 	#HiIntMask,SR			;disable interrupts for exclusion		<24Jul85>

				CLR.L	QLINK(A0)				;clear the link of the element
				TST.L	(A1)+					;anything in the queue? (QHead)
				BNE.S	DOQINSERT				;if so, skip ahead
;
; the queue is empty so make the head and tail point to the new element
;
				MOVE.L	A0,(A1) 				;QTail
				MOVE.L	A0,-(A1)				;QHead
				BRA.S	ENQDONE
;
; insert the element at the end of the list
;
DOQINSERT		MOVE.L	A2,-(SP)				;preserve A2
				MOVE.L	(A1),A2 				;get ptr to old QTail
				MOVE.L	A0,QLINK(A2)			;update its link
				MOVE.L	A0,(A1) 				;update QTail
				MOVE.L	(SP)+,A2				;restore A2
				SUBQ	#4,A1					;point to QHead
;
ENQDONE 		SUBQ	#2,A1					;restore A1
				MOVE	(SP)+, SR				;restore status and go home
				RTS

				ENDP


;
;-----------------------------------------------------------------------
;
; DEQUEUE -- delete an element from a queue. On entry, A0 points to the queue
; element while A1 points to the queue header.	On exit, D0 contains an error
; code.  The only possible error is if the queue element is not present in the
; queue.  All registers except D0 are preserved.
;
;-----------------------------------------------------------------------
;
DEQUEUETRAP		PROC	EXPORT

				MOVE	SR,-(SP)				;preserve status
				MOVEM.L A2-A3,-(SP) 			;preserve work registers
				ORI 	#HiIntMask,SR			;disable interrupts for exclusion		<24Jul85>
;
				MOVE.L	QHEAD(A1),A2			;start searching at the head
				MOVE.L	A2,A3
;
QDELSRCH		CMP.L	A3,A0					;is this the one?
				BEQ.S	GODEL					;(Escher and Bach)if so, go delete it
;
				MOVE.L	A3,A2					;update previous pointer
				MOVE.L	QLINK(A2),A3			;follow the link
				CMP.L	QTAIL(A1),A2			;have we reached the tail?
				BNE.S	QDELSRCH
;
; the queue element can't be found so it's an error
;
				MOVEQ	#QERR,D0
				BRA.S	QDONE1
;
; we found the element so delete it
;
GODEL			CMP.L	A2,A3					;deleting the first element?
				BNE.S	QUNLINK 				;if not, skip
;
; special case to delete the first element in the queue
;
				MOVE.L	QLINK(A2),QHEAD(A1)
				BNE.S	QDELDONE				;was it the only element?
				CLR.L	QTAIL(A1)				;if so, clear the tail too
;
QDELDONE		MOVEQ	#0,D0					;clear the error code
QDONE1			MOVEM.L (SP)+,A2-A3 			;restore work registers
				MOVE	(SP)+, SR				;restore status and go home
				RTS
;
; delete for the general case
;
QUNLINK 		MOVE.L	QLINK(A3),QLINK(A2) 	;unlink it from the chain
				CMP.L	QTAIL(A1),A3			;was it the tail?
				BNE.S	QDELDONE				;if not we're done
				MOVE.L	A2,QTAIL(A1)			;update tail pointer
				BRA.S	QDELDONE

				ENDP


;------------------------------------------------------------------
;
;  INITQUEUE -- initialize the queue header pointed to by A1
;
;------------------------------------------------------------------

INITQUEUE		PROC	EXPORT

				CLR.W	(A1)+					;QFlags
				CLR.L	(A1)+					;qHead
				CLR.L	(A1)					;qTail
				SUBQ	#6,A1					;preserve A1
				RTS
				
				ENDP

				END