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Groups > comp.lang.java.programmer > #4090
| From | Tom Anderson <twic@urchin.earth.li> |
|---|---|
| Newsgroups | comp.lang.java.programmer |
| Subject | Re: Java puzzler |
| Date | 2011-05-15 00:41 +0100 |
| Organization | Stack Usenet News Service |
| Message-ID | <alpine.DEB.2.00.1105150033090.12373@urchin.earth.li> (permalink) |
| References | (8 earlier) <AcCdnflMosQt-lHQnZ2dnUVZ_t2dnZ2d@earthlink.com> <iqhumi$750$1@dont-email.me> <jY-dnS9ZV4RyG1HQnZ2dnUVZ_tadnZ2d@earthlink.com> <alpine.DEB.2.00.1105140954470.12373@urchin.earth.li> <iqm848$52b$1@dont-email.me> |
On Sat, 14 May 2011, markspace wrote: > On 5/14/2011 2:18 AM, Tom Anderson wrote: > >> The semantics of which, i've realised, is an utter can of worms. Does this: >> >> byte b = 100; >> byte c = (b + b) - b; >> >> Throw an exception? > > I have no opinion about that. I'm only interested in cases where the > actual result would be incorrect due to overflow at the machine level. So an expression which might give the right answer, or might blow up, depending on how the compiler felt, is okay, just as long as it never gives the wrong answer? >> One semantics that would work (i think) would be that all expressions >> are evaluated at infinite precision, > > If you've ever actually tried to use BigDecimal with its "infinite > precision" mode, you know that this blows up pretty quickly due to out > of memory errors. The first time you try to evaluate 1/3, it throws an > error. Infinite precision is not the answer. I'm only saying that the semantics would be defined in terms of infinite precision; the implementation could be anything the compiler can come up with which simulates the semantics. Since we're talking about fairly small expressions with integers, i would expect it to do a good job of finding efficient ways to compute things. For example, in the c = (b + b) - b case, it would be free to reduce that to c = b. 'Precision' was a poor choice of word on my part. Since we're talking about integers, there is no precision. We're really talking about infinite width. BigDecimal's problems with primary-school fractions fortunately don't trouble us here. > Once again, I'm only interested in *incorrect results* being detected. > As long as the result can be guaranteed correct, then it's fine, however > the compiler and optimizer choose to implement it. The problem is that not all correct results are practical to compute with finite-width arithmetic. That means that as well as a rule that results have to be correct, we have to have a rule about when results that would be correct explode. tom -- packaheomg sogma's
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Re: Java puzzler Gábor Bakos <aborgabor@gmail.com> - 2011-05-11 01:44 -0700
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-11 05:24 -0700
Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-11 21:57 +0100
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-11 16:07 -0700
Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-12 21:38 +0100
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 13:45 -0700
Re: Java puzzler Nancy 3 <n3@gmai1.c0m> - 2011-05-12 16:56 -0400
Re: Java puzzler markspace <-@.> - 2011-05-12 14:32 -0700
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 16:05 -0700
Re: Java puzzler markspace <-@.> - 2011-05-12 17:40 -0700
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 18:18 -0700
Re: Java puzzler markspace <-@.> - 2011-05-12 19:26 -0700
Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-14 10:18 +0100
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-14 08:09 -0700
Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-14 13:00 -0400
Re: Java puzzler Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-05-14 15:08 -0400
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-14 13:25 -0700
Re: Java puzzler markspace <-@.> - 2011-05-14 08:46 -0700
Re: Java puzzler Spock <spock@starfleet.ufp> - 2011-05-14 19:33 -0400
Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-15 00:41 +0100
Re: Java puzzler markspace <-@.> - 2011-05-14 18:35 -0700
Re: Java puzzler Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-05-14 23:43 -0400
Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-15 11:16 +0100
Re: Java puzzler markspace <-@.> - 2011-05-15 05:40 -0700
Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-15 15:23 +0100
Re: Java puzzler markspace <-@.> - 2011-05-15 08:09 -0700
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 07:37 -0700
Re: Java puzzler markspace <-@.> - 2011-05-15 08:00 -0700
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 08:16 -0700
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 07:35 -0700
Re: Java puzzler markspace <-@.> - 2011-05-15 08:11 -0700
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 08:15 -0700
Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-15 13:11 -0400
Re: Java puzzler Nancy 3 <n3@gmai1.c0m> - 2011-05-12 20:47 -0400
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 18:00 -0700
Re: Java puzzler markspace <-@.> - 2011-05-12 18:01 -0700
Re: Java puzzler Nancy 3 <n3@gmai1.c0m> - 2011-05-12 21:22 -0400
Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 18:32 -0700
Re: Java puzzler Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-12 22:34 -0400
Re: Java puzzler Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-12 22:27 -0400
Re: Java puzzler "John B. Matthews" <nospam@nospam.invalid> - 2011-05-12 00:28 -0400
Re: Java puzzler Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-05-12 10:33 -0400
Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-11 09:12 -0400
Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-11 09:13 -0400
Re: Java puzzler markspace <-@.> - 2011-05-11 08:00 -0700
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