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Path: utzoo!utgpu!water!watmath!clyde!cbatt!ihnp4!meccts!ahby
From: ahby@meccts.UUCP
Newsgroups: comp.sys.apple
Subject: Re: FRE
Message-ID: <2759@meccts.MECC.MN.ORG>
Date: Sat, 16-May-87 01:06:38 EDT
Article-I.D.: meccts.2759
Posted: Sat May 16 01:06:38 1987
Date-Received: Sun, 17-May-87 01:04:09 EDT
References: <8705111018.aa01214@SPARK.BRL.ARPA> <610@fai.UUCP>
Reply-To: ahby@meccts.UUCP (Shane P. McCarron)
Distribution: world
Organization: MECC Technical Services, St. Paul, MN
Lines: 41
Keywords: garbage collection

In article <610@fai.UUCP> dalea@fai.UUCP (Dale M. Arends) writes:
>Unless it was changed by Apple, the BASIC.SYSTEM interpreter has it's own
>version of FRE that is extremely fast.  To call it, instead of FRE(0) issue
>the following ProDOS call:
>
>xx PRINT D$;"FRE" : REM Where xx is the line # and D$ is a CONTROL-D
>
>This can be called as often as desired but should be often enough that the 
>Applesoft FRE(0) routine be avoided.

Actually, I'm pretty sure that BASIC.SYSTEM is constantly monitoring
the bottom of strings/top of arrays area.  If it notices them getting
too close together, it automatically calls its internal fre()
handler.  It will also automatically do a fre whenever you open a file,
it has to allocate a file buffer.  It frees memory by moving the
strings down by 1k or so.

Also, I was pretty sure that ProDOS would spot a call to fre() and
use its internal routine instead of handing it over to Applesoft.
However, I haven't taken a close look at that part of BASIC.SYSTEM 
since its initial beta release in 82(?), so I could be wrong about this.

It is interesting to note that BASIC.SYSTEM is really over-zealous in
the way it hooks into basic.  The link into chrget (I think its
chrget) causes a performance loss of something like 4% off of the
already slow Applesoft!  Also, it has its own internal version of the
BASIC token table, so there is no way to supply additional or changed
tokens to applesoft.  We discovered this when trying to port our
version of extended Applesoft (EBASIC) into the ProDOS world.  We had
defined additional tokens for things like WHILE, CASE, WHEN, ELSE,
SELECT, etc - and there was no way to do this under BASIC.SYSTEM.
Thanks for another piece of software engineering genius, Apple!

If you want a real laugh, take a look at the code inside BASIC.SYSTEM.
Or better yet, look at the color screen dump driver that is supplied
with the Imagewriter II.  Hah!  What a mess!  (giggle, giggle)
-- 
Shane P. McCarron		UUCP	ihnp4!meccts!ahby, ahby@MECC.MN.ORG
MECC Technical Services		ATT	(612) 481-3589
(C) Copyright 1987 Shane P. McCarron
	Redistribution allowed only if your recipients can redistribute