fxpseek.pro
1.82 KB
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;+
; NAME:
; FXPSEEK
;
; AUTHOR:
; Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
; craigm@lheamail.gsfc.nasa.gov
; UPDATED VERSIONs can be found on my WEB PAGE:
; http://cow.physics.wisc.edu/~craigm/idl/idl.html
;
; PURPOSE:
; Internal routine to perform seek on a Unix Pipe.
;
; DESCRIPTION:
;
; See the following procedures for appropriate documentation.
;
; FXGOPEN - open resource
; FXGCLOSE - close resource
; FXGREAD - read from resource
; FXGWRITE - write to resource
; FXGSEEK - seek on resource (i.e., perform POINT_LUN)
;
; FXGFILTERED - determine if resource is a normal file.
;
; PARAMETERS
;
; unit - the pipe LUN. If positive, then the file pointer is moved
; to POSITION in the pipe output. [ In reality the file
; pointer is moved in the cache file. ] If negative, then
; the file pointer of the file unit -LUN is returned in
; POSITION.
;
; position - the file pointer, either passed or returned as defined
; by UNIT.
;
; Side Effects
;
; The file pointer may be updated.
; Actual file accesses are postponed until needed (ie, when FXPREAD
; is called).
;
; MODIFICATION HISTORY:
; Changed copyright notice, 21 Sep 2000, CM
;
; $Id: fxpseek.pro,v 1.2 2001/03/25 18:10:47 craigm Exp $
;
;-
; Copyright (C) 1999-2000, Craig Markwardt
; This software is provided as is without any warranty whatsoever.
; Permission to use, copy, modify, and distribute modified or
; unmodified copies is granted, provided this copyright and disclaimer
; are included unchanged.
;-
PRO FXPSEEK, UNIT, POSITION
@fxpcommn
IF UNIT GT 0 THEN BEGIN
POINT_LUN, CACHE_UNIT(UNIT), POSITION
POINTER(UNIT) = POSITION
ENDIF ELSE BEGIN
POINT_LUN, -CACHE_UNIT(-UNIT), POSITION
POINTER(-UNIT) = POSITION
ENDELSE
RETURN
END