.MCALL	.MODULE
.MODULE	DIRDK,VERSION=02,COMMENT=<Disk directory handler>,IDENT=NO

; Copyright (c) 1998 by Mentec, Inc., Nashua, NH.
; All rights reserved
;
; This software is furnished under a license for use only on a
; single computer system and  may  be  copied  only  with  the
; inclusion of the above copyright notice.  This software,  or
; any other copies thereof, may not be provided  or  otherwise
; made available to any other person except for  use  on  such
; system and to one who agrees to these license  terms.  Title
; to  and  ownership of the software shall at all times remain
; in Mentec, Inc.
;
; The information in this document is subject to change without
; notice and should not be construed as a commitment by Digital
; Equipment Corporation, or Mentec, Inc.
;
; Digital and Mentec  assume  no  responsibility for the use or
; reliability of its software on equipment which is not supplied
; by Digital  or Mentec,  and listed  in the  Software  Product
; Description.
;
; DIR (Directory Program)
;
	.NLIST
	.LIST
	.PSECT	DISK

;+
; Module DIRDK
; This module contains routines to get directory entries for disks.
;-

	.SBTTL	NEXTDK-	Get a disk directory entry

;+
; NEXTDK
; This routine points R5 at the next directory entry of a disk directory.
; R5 cannot be modified once NEXTDK has been called.
; OUTPUTS:
;	R5 -> next directory entry, if one exists
;	C-bit = 1 if no more directory entries
;-

XTERNL	<ILDIR,	INERR>

GBLDAT	<AVAIL,	DE.SIZ,	DH.AVL,	DH.EXB,	DH.HI,	DH.NXT>
GBLDAT	<DH.SIZ,DH.STB,	DS.EOS,	EOSFLG,	HISEG,	IBUF>
GBLDAT	<ICHAN,	INBFSZ,	IOAREA,	NXTDSG,	NXTFIL,	RBLK>
GBLDAT	<SBLOCK,XTRABY>

NEXTDK::TST	EOSFLG		;Have we got a segment?
	BNE	7$		;Branch if yes
1$:	MOV	NXTDSG,RBLK	;Get the next directory segment
	BNE	2$		;If NE then we're not at end
	SEC			;Flag no more entries
	BR	9$		; and return to caller

2$:	MOV	SP,EOSFLG	;Fix the end-of-segment flag
	ASL	RBLK		;Each directory segment is 2 blocks
	ADD	#4,RBLK		;Offset to block 6 for 1st one
	MOV	#IBUF,R5	;Point R5 at the input buffer
	MOV	R5,NXTFIL	;Set the pointer to the next file
	ADD	#DH.SIZ,NXTFIL	;Skip the header words
	.READW	#IOAREA,#ICHAN,R5,#INBFSZ/2,RBLK ;Read a directory segment
	BCC	3$		;Branch if no error
	JMP	INERR		;Else issue the error

3$:	MOV	DH.EXB(R5),XTRABY ;Set the number of extra bytes
	BIT	#1,XTRABY	;Odd number of extra bytes?
	BNE	4$		;Branch if so.  Illegal directory.
	MOV	DH.NXT(R5),NXTDSG ;Set the next directory segment
	MOV	DH.STB(R5),SBLOCK ;Get starting block number for segment
	BNE	5$		;If EQ, then illegal directory
4$:	JMP	ILDIR		;Give "Illegal directory" error

5$:	TST	HISEG		;Is this the first segment?
	BNE	6$		;Branch if not
	MOV	DH.HI(R5),HISEG	;Else get the highest segment open
	MOV	DH.AVL(R5),AVAIL ; and the highest available
	BLE	4$		;If <= 0, illegal directory
	CMP	#37,AVAIL	;Too many directory segments?
	BLO	4$		;Branch if so
6$:	TST	EOSFLG		;Was the last entry end of a segment?
	BEQ	1$		;Branch if so
7$:	MOV	NXTFIL,R5	;Point R5 at the next entry
	BIT	#DS.EOS,@R5	;Are we pointing to end of the segment?
	BEQ	8$		;Branch if not
	CLR	EOSFLG		;Set the flag
8$:	ADD	#DE.SIZ,NXTFIL	;Point to next file entry for next loop
	ADD	XTRABY,NXTFIL	;Don't forget extra bytes
	CLC			;Clear the carry bit
9$:	RETURN

	.END