Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!overload!dillon
From: dillon@overload.Berkeley.CA.US (Matthew Dillon)
Newsgroups: comp.sys.amiga.tech
Subject: Re:  Files larger than available memory.
Message-ID: <dillon.6310@overload.Berkeley.CA.US>
Date: 2 Oct 90 14:07:14 GMT
References: <924@ucsvc.ucs.unimelb.edu.au> <1990Sep23.174736.16118@lavaca.uh.edu> <83986@tut.cis.ohio-state.edu> <14646@cbmvax.commodore.com> <MWM.90Sep25180852@raven.pa.dec.com> <1089@ucsvc.ucs.unimelb.edu.au> <523@public.BTR.COM>
Lines: 48


    I've always envisioned a scheme like this:

    char **Lines;
    long **Storage;
    long NumLines;
    long MaxLines;

    Basically, Lines points to an array of pointers to each line in the
    file.  NumLines specifies the number of lines in the file and MaxLines
    specifies the maximum number of entries in the Lines & Storage arrays
    that have been allocated (determines when you have to reallocate Lines
    due to extending past the MaxLines limit).	Storage points to the
    file position in either the original file or a scratch file.

    Unmodified line, line not in memory
	Lines[i] = NULL;
	Storage[i] = seek-position-in-original-file

    Modified line, line not in memory
	Lines[i] = NULL;
	Storage[i] = 0x80000000 | seek-position-in-scratch-file

    Unmodified line, line in memory
	Lines[i] = <ptr-to-memory>
	Storage[i] = seek-position-in-original-file

    Modified line, line in memory
	Lines[i] = <ptr-to-memory>
	Storage[i] = 0x80000000 | seek-position-in-scratch-file

    In anycase, all that would be required to remain in main memory is
    NumLines * 8 bytes.  You also get random access out of this scheme.
    Additionally, you could implement a locking system (lock line in memory)
    internally to make editor functions more efficient.

    The scratch file would slowly fill up with changes and, upon reaching
    a certain size, would be 'packed' by creating a new scratch file,
    copying pertainent entries, and deleting the old.

					-Matt

--

    Matthew Dillon	    dillon@Overload.Berkeley.CA.US
    891 Regal Rd.	    uunet.uu.net!overload!dillon
    Berkeley, Ca. 94708
    USA