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!newscon02.news.prodigy.com!newscon06.news.prodigy.com!prodigy.net!newsfeed-00.mathworks.com!bigboote.WPI.EDU!news.tufts.edu!uunet!dca.uu.net!spool.news.uu.net!ash.uu.net!newsfd02.forthnet.gr!not-for-mail From: Ioannis Vranos 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: Thu, 24 Mar 2005 03:44:12 +0200 Organization: FORTHnet S.A., Atthidon 4, GR-17671 Kalithea, Greece, Tel: +30 2109559000, Fax: +30 2109559333, url: http://www.forthnet.gr Message-ID: <1111628652.131663@athnrd02> 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> <42309456$1@news.broadpark.no> <1110569032.207770@athnrd02> <1110607809.837000@athnrd02> <1110608948.651588@athnrd02> <1111613984.430545@athnrd02> NNTP-Posting-Host: athnrd02.forthnet.gr Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Trace: athprx02.forthnet.gr 1111628652 11764 193.92.150.73 (24 Mar 2005 01:44:12 GMT) X-Complaints-To: abuse@forthnet.gr NNTP-Posting-Date: Thu, 24 Mar 2005 01:44:12 +0000 (UTC) User-Agent: Mozilla Thunderbird 1.0 (Windows/20041206) X-Accept-Language: en-us, en In-Reply-To: Cache-Post-Path: newsfd02!unknown@ppp16-adsl-51.ath.forthnet.gr Xref: g2news1.google.com comp.lang.ada:9860 comp.lang.c++:46956 comp.realtime:1653 comp.software-eng:5257 Date: 2005-03-24T03:44:12+02:00 List-Id: Dr. Adrian Wrigley wrote: >>Dr. Adrian Wrigley wrote: >> >> >>>And you can do really handy stuff passing arrays not indexed from 0, >>>and accessing the attributes: >>> >>>-- No particular purpose but to demo >>> type MyString is array (Integer range <>) of Integer; >>> >>> procedure UpdateString (Blob : in out MyString; K : Integer) is >>> begin >>> >>> if Blob'Length = 0 then >>> return; >>> elsif Blob'Length = 1 then >>> Blob (Blob'First) := Blob (Blob'First) + K; >>> return; >>> else >>> UpdateString (Blob (Blob'First .. Blob'First+Blob'Length/2-1), 19); >>> UpdateString (Blob (Blob'First+Blob'Length/2 .. Blob'Last), 27); >>> return; >>> end if; >>> >>> end UpdateString; >>>... >>> UpdateString (Fred (10 .. 19), 0); >> >> >>If you provide some explanations, I will give you the C++ equivalent. > > > UpdateString takes an array indexed by integers, updating bottom > and top halves recursively in some obscure way. OK. > > The point is that the input parameter is an array with upper and lower > bounds which are arbitrary, and are different at each level of > recursion. Which provides no real benefit at least in this function. > I have created the arguments to the recursive call > by slicing the input parameter into two half arrays, with the > help of the array attributes ('First, 'Last, 'Length). Normally, > this takes place without any copying. No heap allocation is > required, and any accesses outside the intended array range for > updating at each level of recursion are excepted. > > The most obvious C++ implementation is with vectors, but I think > you need three additional parameters and several checks to get > equivalent semantics. The three new parameters might be > 'StartElement' 'EndElement' and 'BaseOffset'. You need the > BaseOffset to accommodate the vectors always starting at 0, > so you can find the problem-domain start. > > You may get into problems if the procedure needs to call > other functions that take a vector, if they are unable to > take upper and lower limits to process. Can you make a > vector which is a slice of another vector without copying > all the elements in and out? > > This kind of recursive slicing of arrays is something I > have found *much* more natural and reliable in Ada than in C, > where hacking with pointer arithmetic and extra parameters > would be the usual solution. One can use two iterators while passing the length as an extra function parameter. Besides that, nothing else changes. -- Ioannis Vranos http://www23.brinkster.com/noicys