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 %TITLE 'WFREABCK - read previous line'
MODULE WFREABCK (				! Read previous line
		IDENT = '3-001'			! File: WFREABCK.BLI Edit: GB3001
		) =
BEGIN
!COPYRIGHT (c) DIGITAL EQUIPMENT CORPORATION 1981, 1988.  ALL RIGHTS RESERVED.
!
!THIS SOFTWARE IS FURNISHED UNDER A LICENSE AND MAY BE USED AND COPIED ONLY
!IN ACCORDANCE WITH THE TERMS OF SUCH LICENSE AND 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.  NO TITLE
!TO AND OWNERSHIP OF THE SOFTWARE IS HEREBY TRANSFERRED.
!
!THE INFORMATION IN THIS SOFTWARE IS SUBJECT TO CHANGE WITHOUT NOTICE AND 
!SHOULD NOT BE CONSTRUED AS A COMMITMENT BY DIGITAL EQUIPMENT CORPORATION.
!
!DIGITAL ASSUMES NO RESPONSIBILITY FOR THE USE OR RELIABILITY OF ITS 
!SOFTWARE ON EQUIPMENT THAT IS NOT SUPPLIED BY DIGITAL.
!
!
!++
! FACILITY:	EDT -- The DEC Standard Editor
!
! ABSTRACT:
!
!	Read the previous line from the work file system.
!
! ENVIRONMENT:	Runs at any access mode - AST reentrant
!
! AUTHOR: Bob Kushlis, CREATION DATE: October 16, 1978
!
! MODIFIED BY:
!
! 1-001	- Original.  DJS 23-Feb-1981.  This module was created by
!	extracting routine EDT$$RD_PRVLN  from module EDTWF.
! 1-002	- regularize headers.  JBS 19-Mar-1981
! 1-003 - Change index for line numbers from 10 to 15.  SMB 18-Jan-1982
! 1-004	- Remove EDT$$SET_WKLN.  JBS 14-Sep-1982
! 3-001 - Use word addressing for Tops 10/20. GB 17-Feb-1983
!--

%SBTTL 'Declarations'
!
! TABLE OF CONTENTS:
!

REQUIRE 'EDTSRC:TRAROUNAM';

FORWARD ROUTINE
    EDT$$RD_PRVLN;

!
! INCLUDE FILES:
!

REQUIRE 'EDTSRC:EDTREQ';

!
! MACROS:
!
!	NONE
!
! EQUATED SYMBOLS:
!
!	NONE
!
! OWN STORAGE:
!
!	NONE
!
! EXTERNAL REFERENCES:
!
!	In the routine
%SBTTL 'EDT$$RD_PRVLN  - read previous line'

GLOBAL ROUTINE EDT$$RD_PRVLN 			! Read previous line
    =

!++
! FUNCTIONAL DESCRIPTION:
!
!	Read a line backwards.  The line preceding the current line becomes the
!	current line.  If we are already at the top, return a 0 otherwise return
!	a 1.
!
! FORMAL PARAMETERS:
!
!	NONE
!
! IMPLICIT INPUTS:
!
!	CUR_BUF
!	WK_BUK
!	WK_CURBUK
!	LNO0
!	WK_LN
!
! IMPLICIT OUTPUTS:
!
!	CUR_BUF
!
! ROUTINE VALUE:
!
!	1 = previous line read successfully
!	0 = there is no previous line
!
! SIDE EFFECTS:
!
!	NONE
!
!--

    BEGIN

    EXTERNAL ROUTINE
	EDT$$WF_MAKECUR : NOVALUE;

    EXTERNAL
	CUR_BUF : REF TBCB_BLOCK,	! Current text buffer control block
	WK_BUK : 			! Pointer to current bucket
	    REF BLOCK [WF_BUKT_SIZE] FIELD (WFB_FIELDS),
	WK_CURBUK,			! Number of the current bucket
	LNO0 : LNOVECTOR [14],
	WK_LN : REF LIN_BLOCK;		! Pointer to work line

    CUR_BUF [TBCB_CHAR_POS] = 0;
!+
! See if we are at the beginning of a bucket.
!-

    IF (.CUR_BUF [TBCB_LINE_ADDR] EQL WFB_FIXED_SIZE)
    THEN

	IF (.WK_BUK [WFB_PREV_BUKT] EQL 0)
	THEN
	    RETURN (0)				! cannot read backward at beginning of buffer.
	ELSE
	    BEGIN
!+
! Read the previous bucket and position to it's end.
!-
	    EDT$$WF_MAKECUR (.WK_BUK [WFB_PREV_BUKT]);
	    CUR_BUF [TBCB_LINE_ADDR] = .WK_BUK [WFB_END];
	    CUR_BUF [TBCB_CUR_BUKT] = .WK_CURBUK;
	    END;

!+
! Now, move back a line.
!-
    CUR_BUF [TBCB_LINE_ADDR] = .CUR_BUF [TBCB_LINE_ADDR] - .(.WK_BUK + .CUR_BUF [TBCB_LINE_ADDR] - 1);
    SUBLINE (LNO0, CUR_BUF [TBCB_CUR_LIN], CUR_BUF [TBCB_CUR_LIN]);
!+
! Get the address of the current line.
!-
    WK_LN = .WK_BUK + .CUR_BUF [TBCB_LINE_ADDR];
    RETURN (1);
    END;


END
ELUDOM