Xref: utzoo comp.emacs:3695 comp.editors:217 Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!njin!princeton!udel!rochester!cornell!blandy From: blandy@marduk.cs.cornell.edu (Jim Blandy) Newsgroups: comp.emacs,comp.editors Subject: Buffer data structures Summary: What's your favorite? Keywords: data structures, buffers Message-ID: <18612@cornell.UUCP> Date: 26 Jun 88 18:13:10 GMT Sender: nobody@cornell.UUCP Reply-To: blandy@cs.cornell.edu (Jim Blandy) Followup-To: comp.emacs Organization: Cornell Univ. CS Dept, Ithaca NY Lines: 30 Okay everyone - I'm sick and tired of the old linked-list-of-lines and array-of-pointers-to-lines tricks - I've been trying to think of a new, creative data structure where insertion is free, block copies are minimal, memory isn't wasted, and the buffalos roam free (or are they GNUs?) What's the best data structure you've come up with (or heard of) for representing a text buffer? Does it implement true markers (you set them, they stay with their text as things move around)? If a big file shrinks, will the space be returned to the free pool? My favorite is a combination of the 'gap-in-the-middle' approach and the linked list approach. In the gap-in-the-middle approach, the buffer is one contiguous block of memory, where the unused portion acts as a gap for insertion and deletion; you move the gap by shifting characters from one side of it to the other. Once you've got the gap where you want it, insertion is as easy as storing the characters and shrinking the gap; to delete, enlarge the gap to enclose the characters you want gone. (I got this approach from an editor published in some computer magazine WAY BACK. Byte, maybe.) The problem comes when the gap gets filled in; if you've got the whole address space to yourself, you just tell the user "tough luck," but if you're in a multitasking environment, you need to ask for more space; I'd make a linked list of blocks, each with its own gap. If a block is empty, you free its space. Okay, now I've given you my favorite data structure. Feel free to use it if you like. Now what's your favorite? If you'd get fired for revealing it, don't bother, but if you can, post a quick description. -- Jim Blandy - blandy@crnlcs.bitnet "insects were insects when man was just a burbling whatsit." - archie