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-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,78b2880bc7e78e39 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2001-03-28 17:02:05 PST Path: supernews.google.com!sn-xit-03!supernews.com!hermes2.visi.com!news-out.visi.com!news-out.visi.com!hermes.visi.com!nycmny1-snh1.gtei.net!bstnma1-snf1.gtei.net!news.gtei.net!USEAST.RATIONAL.com NNTP-Posting-Host: 172.20.21.30 Newsgroups: comp.lang.ada Date: Wed, 28 Mar 2001 19:52:31 -0500 Message-ID: From: "Corey Ashford" References: <3ab5d2a4$1@pull.gecm.com> Subject: Re: RISC X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.00.2919.6700 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2919.6700 Xref: supernews.google.com comp.lang.ada:6181 Date: 2001-03-28T19:52:31-05:00 List-Id: Why not use signed integer types? You'd get overflow detection for free, via a Constraint_Error exception. For example: type X is new Integer range -128 .. 127; for X'size use 8; "chris.danx" wrote in message news:dwtw6.3343$MD6.241100@news6-win.server.ntlworld.com... > mod types have made some parts of the machine simple but are making > arithmetic operations a nightmare. > > I need to support 2s compliment integers (floats will not feature at all) > hence mod types. Taking not of X and add 1, then it's negative. no probs! > Problem is with sign and overflow on add, sub, mul, div. > > Each one must cope with signed nums and unsigned ones -- signal a carry or > overflow. I think you can just do add/sub and no worries. Problems arise > when i detect overflow, i tried thinking this out, and Martin Dowie pointed > out a possible solution that might work but only for unsigned nums. I don't > know how to go about this signed ones. > > I really need to know how to detect overflow for multiplication and > division. I also need a way to detect it for add and sub. Maybe Ada has an > attribute for this or something, > > e.g. ... > type X is mod 256; > ... > a : x := 128; > a := x + x; > ... > if a'overflow then > ... > end if; > > {i doubt it though!} > > Can anyone help, > > > Thanks, > Chris Campbell > > "Martin Dowie" wrote in message > news:3ab5d2a4$1@pull.gecm.com... > > I had a similar problem recently when I had to mimic unsigned 64 bits with > > only > > unsigned 32 bits available. > > > > For addition and subtract it is fairly easy. e.g. > > > > a = 255, b = 1 > > c = a + b > > if c < a then overflow as it has wrapped > > > > similarly for subtraction with > instead of <. > > > > I only required +/- support, so I'm afraid I have no solutions for * or / > > :-( > > > > The long-hand way for multiplications would be to add e.g. > > a = 90, b = 3 > > c = 0 > > for I in 1 .. b loop > > c = c + a > > if c < a then overflow as it has wrapped > > end loop > > > > not very efficient... > > > > Sorry, no ideas spring to mind for division... > > > > chris.danx wrote in message > > news:qrws6.3335$bL.360000@news6-win.server.ntlworld.com... > > > Two quickies! I hope! > > > > > >[snip] > > > > > > I'm using mod types to simulate registers in the RISC machine. I'm > about > > to > > > implement arithmetic operations but i've thought of a problem. How do i > > > detect overflow? > > > > > > e.g. > > > say it was 1 byte reg > > > > > > 25*158 is too big. > > > > > > 12+254 is too big also. > > > > > > >