From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,703c4f68db81387d
X-Google-Thread: 109fba,703c4f68db81387d
X-Google-Thread: 115aec,703c4f68db81387d
X-Google-Thread: f43e6,703c4f68db81387d
X-Google-Attributes: gid103376,gid109fba,gid115aec,gidf43e6,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!news.glorb.com!border1.nntp.dca.giganews.com!nntp.giganews.com!wn14feed!worldnet.att.net!12.120.4.37!attcg2!ip.att.net!news.binc.net!kilgallen
From: Kilgallen@SpamCop.net (Larry Kilgallen)
Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
Subject: Re: [OT] Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: 28 Mar 2005 11:41:29 -0600
Organization: Berbee Information Networks Corporation
Message-ID: <oiqNGidTC11I@eisner.encompasserve.org>
References: <4229bad9$0$1019$afc38c87@news.optusnet.com.au>
 <1110032222.447846.167060@g14g2000cwa.googlegroups.com>
 <871xau9nlh.fsf@insalien.org>
 <3SjWd.103128$Vf.3969241@news000.worldonline.dk>
 <87r7iu85lf.fsf@insalien.org> <1110052142.832650@athnrd02>
 <hwciddo3rp1S@eisner.encompasserve.org>
 <e39403d5.0503100359.5c975706@posting.google.com>
 <1lr611thktbau$.1dj95z21h7l5v.dlg@40tude.net>
 <e39403d5.0503110005.6586fa3f@posting.google.com>
 <wccis3k1zq0.fsf@shell01.TheWorld.com>
 <kb9f41tmpibkirj29fu2golfsqpefikOrganization: LJK Software
NNTP-Posting-Host: eisner.encompasserve.org
X-Trace: grandcanyon.binc.net 1112031669 18494 192.135.80.34 (28 Mar 2005
 17:41:09 GMT)
X-Complaints-To: abuse@binc.net
NNTP-Posting-Date: Mon, 28 Mar 2005 17:41:09 +0000 (UTC)
Xref: g2news1.google.com comp.lang.ada:10080 comp.lang.c++:47635
 comp.realtime:1785 comp.software-eng:5420
Date: 2005-03-28T11:41:29-06:00
List-Id: <comp.lang.ada>

In article <d29c80$mpp3@cui1.lmms.lmco.com>, "REH" <bogus@nowhere.net> writes:
> 
> "Ioannis Vranos" <ivr@remove.this.grad.com> wrote in message
> news:1112026376.920221@athnrd02...
>> REH wrote:
>>
>> > These will mostly fail on systems with alignment constraints (SPARC,
> PPC,
>> > etc.).
>>
>> Why?
>>
>>
>> -- 
> 
> Well, suppose your class contains a variable of type double, which on some
> systems is 8 bytes and requires 8 byte alignment.  The array you are
> defining to hold the class is a character array, which only requires 1 byte
> alignment.  If it is created with a 1 byte alignment, when you create the
> class in it using placement new, now the double is misaligned.  When you
> access it nasty things can happen.  Intel processors can handled misaligned
> variables, but take extra clock cycles to do so.  On a SPARC or PowerPC, you
> will throw a hardware exception (segmentation fault or machine check most
> likely).  A way around this problem is to either 1) make an array of
> doubles, 2) union the array with a double, or 3) allocate from the heap.

This can depend on the operating system.

On Alpha (and I presume on Itanium) VMS catches such exceptions and fixes
them up.  It slows things down, but the result is still correct.