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Message-ID: <3C734B2D.F82A42FB@yahoo.com>
Date: Wed, 20 Feb 2002 02:07:25 -0500
From: CBFalconer <cbfalconer AT yahoo DOT com>
Organization: Ched Research
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To: djgpp-workers AT delorie DOT com
Subject: Re: Malloc/free DJGPP code
References: <10202200445 DOT AA15769 AT clio DOT rice DOT edu>
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Reply-To: djgpp-workers AT delorie DOT com

Charles Sandmann wrote:
> 
> > If sbrk alignment is controlled malloc alignment is controlled.
> > Pick a size.
> 
> sbrk() alignment is NOT controlled - it is up to malloc to to do
> the alignment.  Alignment should be on an 8 byte boundary to
> maximize performance with floating point arrays.  The overhead per
> block must be a multiple of 8 bytes (at a minimum) to keep the
> blocks aligned.  Larger alignments might add value but not proven.
> 
... snip ...
> 
> I posted both; little feedback on which should be committed.  But it's
> important that the block overhead be a factor of the alignment or you
> will almost never merge blocks.

Important to know.  I would suggest always requesting at least
ALIGN more than needed, so that an unexpected sbrk can be
truncated.  Expected sbrks simply extend the size of the current
lastsbrk, and are automatically aligned.  Unexpected ones have no
bottom adjacencies anyhow.  Once the correction is made in the
first expected sbrk all will be quiet until the next unexpected. 
That leaves the wastage at the bottom of a connected group.

How does my proposal for matching the unclean linkages look,
hopefully by just matching the offset of the size component?

I gather ALIGN = 8 is needed.  I had assumed 4 from the action of
the present system.

-- 
Chuck F (cbfalconer AT yahoo DOT com) (cbfalconer AT XXXXworldnet DOT att DOT net)
   Available for consulting/temporary embedded and systems.
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