Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!airs!ian
From: ian@airs.com (Ian Lance Taylor)
Newsgroups: comp.compression
Subject: Re: Proposed data compression interface standard.
Keywords: data compression interface standard
Message-ID: <1923@airs.com>
Date: 21 Jun 91 05:42:13 GMT
References: <859@spam.ua.oz>
Sender: news@airs.com
Lines: 36

ross@spam.ua.oz.au (Ross Williams) writes:

>2.3 Use of Memory
>-----------------
>2.3.1 A  conforming procedure must read  and write only the  memory in
>the  parameters of  its  parameter list  with  the  exception of  some
>"extra" memory  (which can take the  form of registers or  local stack
>variables)  which  it  may  use for  temporary  use,  subject  to  the
>following conditions:

>   1) The particular language/environment must ensure that the memory
>      will be available (i.e. failure during allocation is impossible).
>   2) The total size of the extra memory does not exceed 1024 bytes.
>   3) The memory is not used to transfer information in or out of the
>      instantiation of the conforming procedure.

This doesn't quite make sense to me as written, although this is
really just nitpicking.  The program itself is probably in memory, and
it surely acceptable to read it.  It is surely also acceptable to use
some sort of constant table during compression (a precomputed
frequency count, perhaps).  Finally, restriction 3 appears to prohibit
the accumulation of statistics across several calls; if those
statistics do not affect the compression, but merely provide
information that the program can access in some non-standard fashion,
why prohibit them?

>2.6.3 The  identity record must  contain the information  contained in
>the fields of the following "model" record:

How about a field for the version number of the standard, so that new
fields can be more easily added to this record?
-- 
Ian Taylor                   ian@airs.com                 uunet!airs!ian
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