mirror of https://github.com/GnoConsortium/gno.git
115 lines
4.2 KiB
Plaintext
115 lines
4.2 KiB
Plaintext
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Release Notes for STEVIE - Version 3.10a
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Source Notes
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Tony Andrews - March 6, 1988
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Overview
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--------
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This file provides a brief description of the source code for
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Stevie. The data structures are described later as well. For information
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specific to porting the editor, see the file 'porting.doc'. This document
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is more relevant to people who want to hack on the editor apart from doing
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a simple port.
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Most of this document was written some time ago so a lot of the
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discussion centers on problems related to the Atari ST environment and
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compilers. Most of this can be ignored for other systems.
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Things You Need - ATARI
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-----------------------
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Stevie has been compiled with both the Alcyon (4.14A) and the
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Megamax C compilers. For the posted binary, Megamax was used because
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it's less buggy and provides a reasonable malloc(). Ports to other
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compilers should be pretty simple. The current ifdef's for ALCYON and
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MEGAMAX should point to the potential trouble areas. (See 'porting.doc'
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for more information.)
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The search code depends on Henry Spencer's regular expression
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code. I used a version I got from the net recently (as part of a 'grep'
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posting) and had absolutely no trouble compiling it on the ST. Thanks,
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Henry!
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The file 'getenv.c' contains a getenv routine that may or may
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not be needed with your compiler. My version works with Alcyon and
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Megamax, under either the Beckemeyer or Gulam shells.
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Lastly, you need a decent malloc. Lots of stuff in stevie is
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allocated dynamically. The malloc with Alcyon is problematic because
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it allocates from the heap between the end of data and the top of stack.
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If you make the stack big enough to edit large files, you wind up
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wasting space when working with small files. Mallocs that get their memory
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from GEMDOS (in fairly large chunks) are much better.
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Things You Need - AMIGA
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-----------------------
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Lattice C version 5.0 or later.
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Data Structures
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---------------
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A brief discussion of the evolution of the data structures will
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do much to clarify the code, and explain some of the strangeness you may
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see.
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In the original version, the file was maintained in memory as a
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simple contiguous buffer. References to positions in the file were simply
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character pointers. Due to the obvious performance problems inherent in
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this approach, the following changes were made.
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The file is now represented by a doubly linked list of 'line'
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structures defined as follows:
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struct line {
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struct line *next; /* next line */
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struct line *prev; /* previous line */
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char *s; /* text for this line */
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int size; /* actual size of space at 's' */
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unsigned long num; /* line "number" */
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};
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The members of the line structure are described more completely here:
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prev - pointer to the structure for the prior line, or NULL for the
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first line of the file
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next - like 'prev' but points to the next line
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s - points to the contents of the line (null terminated)
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size - contains the size of the chunk of space pointed to by s. This
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is used so we know when we can add text to a line without getting
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more space. When we DO need more space, we always get a little
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extra so we don't make so many calls to malloc.
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num - This is a pseudo line number that makes it easy to compare
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positions within the file. Otherwise, we'd have to traverse
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all the links to tell which line came first.
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Since character pointers served to mark file positions in the
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original, a similar data object was needed for the new data structures.
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This purpose is served by the 'lptr' structure which is defined as:
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struct lptr {
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struct line *linep; /* line we're referencing */
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int index; /* position within that line */
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};
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The member 'linep' points to the 'line' structure for the line containing
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the location of interest. The integer 'index' is the offset into the line
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data (member 's') of the character to be referenced.
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The following typedef's are more commonly used:
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typedef struct line LINE;
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typedef struct lptr LPtr;
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Many operations that were trivial with character pointers had to be
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implemented by functions or macros to manipulate LPtr's. Most of these are in
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the files 'ptrfunc.c' and 'macros.h'. There you'll find functions to increment,
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decrement, and compare LPtr's.
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