Newsgroups: comp.editors
Path: utzoo!utgpu!watserv1!watmath!mks.com!ant
From: ant@mks.com (Anthony Howe)
Subject: Re: REPOST: editor.101
Date: Wed, 12 Jun 91 14:39:30 GMT
Message-ID: <1991Jun12.143930.14186@mks.com>
Organization: Mortice Kern Systems, Waterloo, Ontario, CANADA
References: <1991Jun4.155657.4357@mks.com> <1991Jun11.195732.25500@wpi.WPI.EDU>

rcarter@wpi.WPI.EDU (Randolph Carter (nee. Joseph H. Allen)) writes:
>Another buffer technique I recently found is the "pieces" method from the
>pointing editor (I can't remember the author's name).  As you edit, you break
 ^^^^^^^^^^^^^^^
What and where?  Could you find a reference.  This might make for another
article -- Editor.202 maybe.

>a contiguous buffer up into pieces and add or delete characters from the edges
>of the pieces.  Each piece is stored in a malloc-like structure in a virtual
>memory file.  You have to maintain a list of all the pieces and search through
>this list when you move out of a piece.  You also glue pieces together when
>possible.  This is a neat technique, but it's complicated.

This sounds like a variation of the scratch file method described in
"Software Tools" chapter 6.  (I'm hoping to write an Editor.201 article
based on this chapter later this summer.)

>An important technique for this and other buffer methods is to have routines
>which adjust pointer/size pairs as you move between pieces (or blocks or over
>the gap).  This way, high level routines (like screen update) only have to
>keep track of the pointer and size and can simply call a function to update
>these when the beginning or end of a block is reached.  

Why sizes?  (I'm a bit slow this morning)

>Another usefull technique is to try to keep buffer pointers in the form of a
>byte offset from the beginning of the file in the buffer.  There then needs to
>be logical to physical translation functions but keeping the pointer this
>simple will make implementing higher level functions much easier.

This technique is fine for the Buffer Gap Scheme, but I don't see how this
would apply in a Link List Scheme.  Link List and Pieces would require that 
pointers become structures suitable for the scheme n'est pas?  

- ant
-- 
ant@mks.com                                                   Anthony C Howe 
Mortice Kern Systems Inc. 35 King St. N., Waterloo, Ontario, Canada, N2J 6W9
"Fate favors fools, small children, and ships named Enterprise" - Riker