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From: mike@unmvax.UUCP
Newsgroups: comp.lang.c,comp.unix.questions
Subject: Re: Optimizing use of malloc
Message-ID: <695@unmvax.unm.edu>
Date: Mon, 2-Nov-87 01:34:50 EST
Article-I.D.: unmvax.695
Posted: Mon Nov  2 01:34:50 1987
Date-Received: Wed, 4-Nov-87 06:07:22 EST
References: <7264@brl-adm.ARPA> <1015@cup.portal.com> <126@fxgrp.UUCP> <1665@geac.UUCP>
Sender: news@unmvax.unm.edu
Reply-To: mike@turing.unm.edu (Michael I. Bushnell)
Followup-To: comp.lang.c
Organization: University of New Mexico, Albuquerque
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Xref: utgpu comp.lang.c:4984 comp.unix.questions:4238
In-reply-to: daveb@geac.UUCP

In article <1665@geac.UUCP>, daveb@geac writes:
~In article <4753@oberon.USC.EDU> you write:
~>Most versions of malloc will round the amount of memory you request to
~>some number convienient for it.  Since the pointer returned must be
~>maximally alligned, this is normally a multiple of the size of the
~>largest type.  What I need to know what sizes of memory requests to
~>malloc will reduce wasted space for a variety of systems: 

~  The basic rule is laid down by the hardware designers: if a machine
~will fetch longwords from a byte address, its a don't-care. If it
~requires an even address, use int alignment.  Otherwise use long.
~IBM /376's can require double! (/370's require long).
~  The information should vary mostly with cpu-chip, and can be
~obtained from CPU manuals.

This is not the whole story.  On BSD, malloc uses a binary buddy
system.  So, if you request 33 longs of data, you are liable to get
more like 60.  (Not 64, because there is some header information kept
for free().)
--
				Michael I. Bushnell
				a/k/a Bach II
				mike@turing.unm.edu
				{ucbvax,gatech}!unmvax!turing!mike
---
Those aren't WINOS--that's my JUGGLER, my AERIALIST,
 my SWORD SWALLOWER, and my LATEX NOVELTY SUPPLIER!!
				-- Zippy the Pinhead
				Michael I. Bushnell
				a/k/a Bach II
				mike@turing.unm.edu
				{ucbvax,gatech}!unmvax!turing!mike
---
Those aren't WINOS--that's my JUGGLER, my AERIALIST,
 my SWORD SWALLOWER, and my LATEX NOVELTY SUPPLIER!!
				-- Zippy the Pinhead