*************************************************************
          *                                                           *
          *     VMP$MAPFILE - Vicki Woolf's file mapping procedures   *
          *                                                           *
          *                  Software specification                   *
          *                       (02-FEB-80)                         *
          *                                                           *
          *************************************************************

	  VICKI WOOLF
	  PROGRAM OF COMPUTER GRAPHICS - CORNELL UNIVERSITY
	  120 RAND HALL   ITHACA   NEW YORK  14853

1) Mapping to a file:

    Calling format:
	retstatus = VMP$MAP_FILE(id,spec,type,access,
	2                        windowsize,filelength)

    Inputs:
	spec		= CHARACTER file specification
	type		= CHARACTER file type  ('OLD','NEW')
	access		= CHARACTER file access  ('R/O','R/W')
	windowsize	= INTEGER*4 number of bytes in mapping window

    Outputs:
	id		= INTEGER*4 file identification number
	filelength	= INTEGER*4 number of bytes in file
	retstatus	= INTEGER*4 return status  (to be defined)

    Action:
	Open the specified file, returning a unique identification
	number and the total number of bytes in the file to the
	caller (return filelength of zero if new file).
	No mapping is performed by this procedure.


2) Unmapping from a file:

    Calling format:
	retstatus = VMP$UNMAP_FILE(id,filelength)

    Inputs:
	id		= INTEGER*4 file identification number
	filelength	= INTEGER*4 number of bytes in file

    Outputs:
	retstatus	= INTEGER*4 return status  (to be defined)

    Action:
	Update, unmap and close the file, either extending or
	truncating the file to the specified number of bytes.


3) Finding a record:

    Calling format:
	retstatus = VMP$MAP_RECORD(id,recposition,reclength,address)

    Inputs:
	id		= INTEGER*4 file identification number
	recposition	= INTEGER*4 byte position of record in file  (0...)
	reclength	= INTEGER*4 number of bytes in record  (1..windowsize)

    Outputs:
	address		= INTEGER*4 virtual address of record
	retstatus	= INTEGER*4 return status  (to be defined)

    Action:
	For any specified recposition,  this procedure returns
	a virtual address through which at least reclength bytes
	starting at that position may be accessed by the caller.
	For file reading, this length is set by the caller to the
	largest record expected to occur in the file.  For writing,
	it is set to the actual length of the record being written.
	If the specified position is beyond the current end-of-file,
	the file is extended as necessary  (subject to access flag).